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We study D and DS mesons at finite temperature using an effective field theory based on chiral and heavy-quark spin-flavor symmetries within the imaginary-time formalism. Interactions with the light degrees of freedom are unitarized via a Bethe-Salpeter approach, and the D and self-energies are calculated self-consistently. We generate dynamically the e D∗0(2300)and Ds(2317)state, and study their possible identification as the chiral We study Dand Dsmesons at finite temperature using an effective field theory based on chiral and heavy-quark spin-flavor symmetries within the imaginary-time formalism. Interactions with the light degrees of freedom are unitarized via a Bethe-Salpeter approach, and the Dand Dsself-energies are calculated self-consistently. We generate dynamically the D∗0(2300)and Ds(2317)states, and study their possible identification as the chiral partners of the Dand Dsground states, respectively. We show the evolution of their masses and decay widths as functions of temperature, and provide an analysis of the chiral-symmetry restoration in the heavy-flavor sector below the transition temperature. In particular, we analyse the very special case of the D-meson, for which the chiral partner is associated to the double-pole structure of the D∗0(2300).
The small photoreceptor Photoactive Yellow Protein (PYP) enters a reversible photocycle after excitation with blue light. The intermediate states are formed on timescales ranging from femtoseconds to seconds including chromophore isomerization and protonation as well as large structural rearrangements. To obtain local dynamic information the vibrational label thiocyanate (SCN) can be inserted site-specifically at any desired position in the protein by cysteine mutation and cyanylation. The label's CN stretch vibration is highly sensitive to polarity, hydrogen bonding interactions and electric fields and is spectrally well separated from the overlapping protein absorptions. During the course of this thesis it was impressively demonstrated that the successful incorporation of the SCN label at selected positions in PYP provides a powerful tool to study structure changes and dynamics during the photocycle and enhance the local information that are obtained by infrared (IR) spectroscopic methods. Hence the SCN-labeled protein mutants were studied under equilibrium (steady-state) and non-equilibrium conditions.
Examination of the SCN absorption by FTIR spectroscopy showed the influence of various local environments on the label for different locations in the dark state. The response of the label under illumination with blue light reveals information about structural changes in the signaling state. Additional information for both states were obtained by the vibrational lifetime of the CN vibration measured via ultrafast IR-pump-IR-probe experiments. This observable is particularly sensitive for solvent exposure of the label. Time-resolved IR spectroscopy proved to be an excellent method to follow the protein dynamics throughout most part of the photocycle on a hundreds of femtoseconds to milliseconds timescale. By close inspection of protein and chromophore dynamics in wildtype-PYP over nine decades in time, new insights into the changes leading to the proposed photocycle intermediates were obtained. The investigation of the SCN label allowed to follow the different transient structure changes with high local resolution. Depending on its position within the protein the response of the label provided additional information on the photocycle transitions.
The insights that are obtained by the different observables in the steady-state and by the reaction of the SCN label to formation of the different intermediate states during the photocycle contribute to an improved understanding of local, light-induced structure changes in the photoreceptor PYP. This comprehensive study demonstrated the potential provided by the application of SCN as IR label for investigation of protein dynamics.
Proteine sind die Maschinen der Zellen. Um die Funktionalität von zahlreichen zellulären Prozessen zu gewährleisten, müssen Kommunikationssignale innerhalb von Proteinen weitergeleitet werden. Die Weiterleitung einer Störung an einem Ort im Protein zu einer entfernten Stelle, an welcher sie strukturelle und/oder dynamische Änderungen auslöst, wird Allosterie genannt. Zunächst wurde Allosterie hauptsächlich mit großräumigen Konformationsänderungen in Verbindung gebracht, aber später entwickelte sich ein dynamischerer Blickwinkel auf Allosterie in Abwesenheit dieser großräumigen Konformationsänderungen. Die Idee eines allosterischen Pfades bestehend aus konservierten und energetisch gekoppelten Aminosäuren, welche die Signalweiterleitung zwischen entfernten Stellen im Protein vermitteln, entstand. Diese allosterischen Pfade wurden durch zahlreiche theoretische Studien in Zusammenhang mit Pfaden effizienten anisotropen Energieflusses gebracht. Der Energiefluss entlang dieser Netzwerke verknüpft allosterische Signalübertragung mit Schwingungsenergietransfer (VET - vibrational energy transfer). Die Großzahl der Forschungsarbeiten über dynamische Allosterie basiert auf theoretischen Methoden, weil nur wenige geeignete experimentelle Verfahren existieren. Um diesen essentiellen biologischen Prozess der Informationsübertragung besser verstehen zu können, ist die Entwicklung neuer und leistungsstarker experimenteller Instrumente und Techniken daher dringend erforderlich. Die vorliegende Dissertation setzt sich dies zum Ziel.
VET in Proteinen ist aufgrund der Proteingeometrie inhärent anisotrop. Alle globulären Proteine besitzen Kanäle effizienten Energieflusses, von denen vermutet wird, dass sie wichtig für Proteinfunktionen, wie die schnelle Ableitung von überschüssiger Wärme, Ligandenbindung und allosterische Signalweiterleitung, sind. VET kann mit zeitaufgelöster Infrarot (IR) Spektroskopie untersucht werden, bei welcher ein Femtosekunden Anregepuls eines Lasers Schwingungsenergie in ein molekulares System an einer bestimmten Stelle injiziert und ein, nach einem veränderbarem Zeitintervall folgender, IR Abfragepuls die Ausbreitung dieser Schwingungsenergie detektiert. Ein protein-kompatibler und universell einsetzbarer Chromophor, der die Energie eines sichtbaren Photons in Schwingungsenergie konvertiert, wird als Heizelement benötigt um langreichweitige VET Pfade in Proteinen kartieren zu können. Der Azulen (Azu) Chromophor eignet sich dafür, weil er nach Photoanregung des ersten elektronischen Zustandes durch ultraschnelle interne Konversion fast die gesamte injizierte Energie innerhalb von einer Picosekunde in Schwingungsenergie umwandelt. Eingebettet in die nicht-kanonische Aminosäure (ncAA - non-canonical amino acid) ß-(1-Azulenyl)-L-Alanine (AzAla), kann der Azu Rest in Proteine eingebaut werden. Die Ankunft der injizierten Schwingungsenergie an einer bestimmten Stelle im Protein kann mithilfe eines IR Sensors detektiert werden. Die Kombination aus Azu als VET Heizelement und Azidohomoalanine (Aha) als VET Sensor mit transienter IR (TRIR) Spektroskopie wurde schon erfolgreich an kleinen Peptiden in der Dissertation von H. M. Müller-Werkmeister getestet, die der vorliegenden Dissertation in den Laboren der Bredenbeck Gruppe vorausging.
Die Schwingungsfrequenz chemischer Bindungen ist hochempfindlich auf selbst kleine Änderungen der Konformation und Dynamik in der unmittelbaren Umgebung und kann mit IR Spektroskopie gemessen werden, z. B. mit Fourier Transform IR (FTIR) Spektroskopie. IR Spektroskopie bietet eine außergewöhnlich gute Zeitauflösung, die es ermöglicht, dynamische Prozesse in Molekülen auf einer Zeitskala von wenigen Picosekunden zu beobachten, wie z. B. die ultraschnelle Weiterleitung von Schwingungsenergie. Mit zweidimensionaler (2D)-IR Spektroskopie können die Relaxation von schwingungsangeregten Zuständen und strukturelle Fluktuationen um die schwingende Bindung untersucht werden. Allerdings geht die herausragende Zeitauflösung mit limitierter spektraler Auflösung einher. In größeren Molekülen mit zahlreichen Bindungen überlagern sich die Schwingungsbanden und die Ortsauflösung geht verloren. Um diese Limitierung zu überwinden, können IR Marker benutzt werden, chemische Gruppen, die in einer spektral durchsichtigen Region des Protein/Wasser Spektrums (1800 bis 2500 cm-1) absorbieren. Als ncAA können sie kotranslational in Proteine an einer gewünschten Stelle eingebaut werden und so ortsspezifische Informationen aus dem Proteininneren liefern. Aufgrund ihrer geringen Größe, eines relativ großen Extinktionskoeffizientens (350-400 M-1cm-1) und einer hohen Empfindlichkeit auf Änderungen in der lokalen Umgebung sind organische Azide (N3) wie zum Beispiel Aha besonders geeignete IR Marker. Aha kann als Methionin Analogon ins Protein eingebaut werden.
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Während den ersten Mikrosekunden nach dem Urknall glaubt man, dass unser Universum aus einer heißen, dichten und stark wechselwirkenden Materie bestanden haben soll, welche man das Quark-Gluonen-Plasma (QGP) nennt.
In diesem Medium sind die elementaren Bausteine der Materie, die Quarks und die Gluonen, nicht mehr in Hadronen gebunden, sondern können sich stattdessen wie quasi-freie Teilchen verhalten.
Für die ALICE Kollaboration an CERN's Large Hadron Collider (LHC) ist die Untersuchung dieses Mediums eines der Hauptziele. Um dieses Medium im Labor zu erzeugen, werden Protonen und Nukleonen auf nahezu Lichtgeschwindigkeit beschleunigt und anschließend zur Kollision gebracht. Dabei werden Schwerpunktsenergien von bis zu 13 TeV bei Proton-Proton (pp) Kollisionen und bis zu 5.02 TeV bei Blei-Blei (Pb--Pb) Kollisionen erreicht.
Bei solchen hochenergetischen Kollisionen werden die kritischen Werte der Energiedichte und Temperatur von jeweils ungefähr 1 GeV/c und undgefähr 155 MeV überschritten, welche mithilfe von "lattice QCD" bestimmt wurden. Sie bieten daher die perfekten Voraussetzungen für einen Phasenübergang von normaler Materie zu einem QGP.
Die Entwicklung eines solchen Mediums, beginnend bei der eigentlichen Kollision, gefolgt von der Ausbildung des Plasmas und der letztendlichen Hadronisierung, kann jedoch nicht direkt untersucht werden, da das Plasma eine extrem kurze Lebensdauer hat.
Die Studien die das QGP untersuchen möchten, müssen sich deshalb auf Teilchenmessungen und deren Veränderung aufgrund von Einflüssen durch das Medium beschränken.
Es ist noch nicht definitiv geklärt, ob sich ein QGP nur in Kollisionen schwerer Ionen bildet, oder ob dies auch in kleineren Kollisionssystemen wie Proton-Proton oder Proton-Blei der Fall ist.
Damit in dieser Thesis Einschränkungen bezüglich einer möglichen Erzeugung eines mini-GQP in kleinen Kollisionssystemen gemacht werden kann, wird der Fokus auf Messungen von neutralen Pionen und Eta Mesonen mit dem ALICE Detektor am CERN LHC gesetzt. Hierfür wird in einem Referenzsystem von Proton-Proton Kollisionen bei sqrt(s)=8 TeV und in einem Proton-Blei (p--Pb) System bei sqrt(sNN)=8.16 TeV, welches eine nukleare Modifikation erfährt, gemessen und die Ergebnisse verglichen.
Da in Proton-Proton Kollisionen die Bildung eines QGP, aufgrund zu geringer Energiedichte, nicht erwartet wird, dient eine Messung in diesem System als Messbasis, um Effekte der Kollision selbst von Effekten nach der Kollision zu separieren, welche die Teilchenproduktion beeinflussen.
Teilchen können zusätzlich zu dem QGP auch mit kalter Kernmaterie interagieren, was sich in asymmetrischen Proton-Blei Kollisionen testen lässt. In diesem Kollisionssystem wird größtenfalls ein vergleichsweise kleines QGP gebildet, wohingegen das Blei Ion selbst als kalte Kernmaterie agieren kann.
Zusätzlich zu den Mesonenmessungen wird in dieser Thesis auch die Erzeugung von direkten Photonen bei niedrigen Transversalimpulsen (pT) in multiplizitätsabhängigen p--Pb Kollisionen bei einer Schwerpunktsenergie von sNN=5.02 TeV gemessen, welche als direkte Probe, sowie als charakteristisches Signal des QGP gilt.
Die neutralen Pionen, welche in dieser Thesis gemessen werden, kann man als einen Überlagerungszustand der zwei leichtesten Quarksorten, dem "up" (u) und dem "down" (d) Quark, sowie deren entsprechenden Anti-Teilchen verstehen.
Das eta meson hingegen hat einen zusätzlichen Anteil des "strange" Quarks und eine resultierende höhere Masse.
Quarks sind Teil des Standardmodells der Teilchenphysik, welches die Elementarteilchen und die zwischen ihnen wirkenden Elementarkräfte, ausgeübt durch Bosonen, beschreibt.
Das Modell umfasst insgesamt sechs Quarks, welche sich durch ihre Masse und Ladung unterscheiden und als Grundbestandteil von gebundenen Zuständen, sogenannten Hadronen, fungieren.
Die "up" und "down" Quarks gelten hierbei als die leichtesten Quarks und kommen daher am häufigsten in der Natur vor. Das bekannteste Beipiel stellen hier die allgemein bekannten Protonen (uud) und Neutronen (udd) dar, welche die Grundkomponenten von Nukleonen sind.
Die restlichen Quarks tragen eine deutlich höhere Masse und haben daher eine große Tendenz, sich in leichtere Quarks umzuwandeln, wodurch ihre Lebensdauer sehr gering ist. Die "top" und "bottom" Quarks, welche die Schwersten sind, können daher nicht in gewöhnlicher Materie gefunden werden.
Sie können jedoch experimentell durch hoch energetische Teilchenkollisionen erzeugt werden und indirekt über ihre Zerfallsprodukte nachgewiesen werden.
Quarks tragen eine elektrische Ladung von entweder 1/3 oder 2/3, sowie eine Farbladung, wobei Letztere verantwortlich für ihre Bindung in Hadronen ist.
Hadronen bestehen entweder aus drei Quarks, dann werden sie Baryonen genannt, oder aus einem Quark-Antiquark Paar, welches Meson genannt wird.
Diese gebundenen Zustände erfüllen eine insgesamt neutrale Farbladung, sowie eine vollzählige elektrische Ladung.
Des Weiteren gibt es auch exotische Penta-Quark Zustände, welche aus vier Quarks und einem Antiquark bestehen und bereits experimentell nachgewiesen wurden.
Aufgrund der starken Wechselwirkung, welche durch Gluonen vermittelt wird, können Quarks nicht einzeln beobachtet werden.
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Rethinking superdeterminism
(2020)
Quantum mechanics has irked physicists ever since its conception more than 100 years ago. While some of the misgivings, such as it being unintuitive, are merely aesthetic, quantum mechanics has one serious shortcoming: it lacks a physical description of the measurement process. This “measurement problem” indicates that quantum mechanics is at least an incomplete theory—good as far as it goes, but missing a piece—or, more radically, is in need of complete overhaul. Here we describe an approach which may provide this sought-for completion or replacement: Superdeterminism. A superdeterministic theory is one which violates the assumption of Statistical Independence (that distributions of hidden variables are independent of measurement settings). Intuition suggests that Statistical Independence is an essential ingredient of any theory of science (never mind physics), and for this reason Superdeterminism is typically discarded swiftly in any discussion of quantum foundations. The purpose of this paper is to explain why the existing objections to Superdeterminism are based on experience with classical physics and linear systems, but that this experience misleads us. Superdeterminism is a promising approach not only to solve the measurement problem, but also to understand the apparent non-locality of quantum physics. Most importantly, we will discuss how it may be possible to test this hypothesis in an (almost) model independent way.
In this paper we present first-order reversal curve (FORC) diagrams of ensembles of three-dimensional Co3Fe nanostructures as 2 × 2 arrays of nano-cubes and nano-trees. The structures are fabricated and investigated by an advanced platform of focused electron beam induced deposition combined with high-resolution detection of magnetic stray fields using a home-built micro-Hall magnetometer based on an AlGaAs/GaAs heterostructure. The experimental FORC diagrams are compared to macrospin simulations for both geometries at different angles of the externally applied magnetic field. The measured FORC diagrams are in good agreement with the simulated ones and reflect non-uniform magnetization reversal dominated by multi-vortex states within, and strong magnetic coupling between, the building blocks of our nanostructures. Thus, a FORC analysis of small arrays of 3D magnetic nanostructures provides more detailed insights into the mechanisms of magnetization reversal beyond standard major hysteresis loop measurements.
Focused electron beam induced deposition (FEBID) is a direct-write nanofabrication technique able to pattern three-dimensional magnetic nanostructures at resolutions comparable to the characteristic magnetic length scales. FEBID is thus a powerful tool for 3D nanomagnetism which enables unique fundamental studies involving complex 3D geometries, as well as nano-prototyping and specialized applications compatible with low throughputs. In this focused review, we discuss recent developments of this technique for applications in 3D nanomagnetism, namely the substantial progress on FEBID computational methods, and new routes followed to tune the magnetic properties of ferromagnetic FEBID materials. We also review a selection of recent works involving FEBID 3D nanostructures in areas such as scanning probe microscopy sensing, magnetic frustration phenomena, curvilinear magnetism, magnonics and fluxonics, offering a wide perspective of the important role FEBID is likely to have in the coming years in the study of new phenomena involving 3D magnetic nanostructures.
The requirement of the versatile signal generator has always been evident in modern RF and communication systems. The most conventional technique, voltage control oscillator (VCO), has inferior phase noise and narrow bandwidth despite its operating frequency can be up to the sub-THz regime. Its phase noise influenced by a various parameter associated with the oscillator circuit e.g. transistor size \& noise, bias current, noise leaking from the bias supply etc. The bandwidth is limited because the input voltage \& the output frequency of the VCO is not strictly linear over the tuning range. The phase noise and SFDR of the VCO output are enhanced by using the phase-lock technique. The phase-locked loop (PLL) uses the feedback system locking the reference frequency set by the VCO. However, the settling time of the PLL is higher due to a feedback control loop. The higher settling time increases the frequency switching time between PLL outputs. IG-oscillators is suitable for multi-GHz range and wide bandwidth application. Signal generation can alos be achieved by the free-electron radiation, optical lasers, Gunn diodes as well and they can operate even at the THz domain. All these signal generators suffer from slow frequency switching, lack of digital controllability, and advance modulation capability even though their frequency of operation is THz regime. Alternatively, the AWG (arbitrary wave generator) can produce a wide range of frequencies with low phase noise, including digital controllability. One of the vital components of the AWG is the direct digital synthesiser (DDS). Generally, it is composed of a phase accumulator, digital to analogue converter, sine mapping circuits and low pass filter. It needs a reference clock that acts as samples of the DDS outputs. Its output frequency can be varied by applying an appropriate digital input code. But high-speed DDS has several limitations; such as low number of output frequency points, lack of phase control unit, high power consumptions etc. This work addresses such limitations.
Hofstadter-Hubbard physics
(2020)
The Hofstadter model, besides the Haldane and Kane-Mele models, is the most common tight-binding model which hosts topologically nontrivial states of matter. In its time-reversal-symmetric formulation the model can even describe topological insulators. Experimentally, the Hofstadter model was realized with ultracold quantum gases in optical lattices which is a wellcontrolled way to engineer quantum states of tight-binding Hamiltonians. Another established control parameter in ultracold quantum gases are twoparticle, on-site interactions, also known as Hubbard interactions. This work aims at introducing the reader to the concepts of topological states of matter, a collection of corresponding tight-binding models, and the methodology to treat interacting topological states with dynamical mean-field theory.We present recent results for inhomogeneous, interacting systems, spinimbalanced magnetic systems, propose experimental detection methods, and extensions to three-dimensional topological states.
This Dissertation deals with the development of FAIR-relevant X-ray diagnostics based on the interaction of lasers and particle beams with matter. The associated experimental methods are supposed to be employed in the HIHEX-experiments in the HHT-cave of the GSI Helmholtz Center for Heavy-Ion Research GmbH (GSI) in Phase-0 and in the APPA-cave at the Facility for Antiproton and Ion Research in Darmstadt, Germany.
Diagnostic of high aerial density targets that will be used in FAIR experiments demands intense and highly penetrating X-ray sources. Laser generated well-directe relativistic electron beams that interact with high Z materials is an excellent tool for generation of short-pulse high luminous sources of MeV-gammas.
In pilot experiments carried out at the PHELIX laser system, GSI Darmstadt, relativistic electrons were produced in a long scale plasma of near critical electron density (NCD) by the mechanism of the direct laser acceleration (DLA). Low density polymer foam layers preionised by a well-defined nanosecond laser pulse were used as NCD targets. The analysis of the measured electron spectra showed up to 10- fold increase of the electron "temperature" from T_Hot = 1–2 MeV, measured for the case of the interaction of 1–2 ×10^19 Wcm^(−2) ps-laser pulse with a planar foil, up to 14 MeV for the case when the relativistic laser pulse propagates through the by a ns-pulse preionised foam layer. In this case, up to 80–90 MeV electron energy was registered. An increase of the electron energy was accompanied by a strong increase of the number of relativistic electrons and well-defined directionality of the relativistic electron beam measured to be (12 ±1)° (FWHM). This directionality increases the gamma flux on target by far compared to the soft X-ray sources.
Additionally to laser based active diagnostics, passive techniques involving inherent X-ray fluorescence radiation of projectile and target emitted during heavy-ion target interaction can be used to measure the ion beam distribution on shot. This information is of great importance, since the target size is chosen to be smaller than the beam focus in order to ensure homogeneous heating of the HIHEX-target by the ion beam. High amounts of parasitic radiation and activation of experimental equipment is expected for experiments at the APPA-cave. For this reason, all electronic devices must be placed at a safe distance to the target chamber. In order to transport the signal over a large distance, the X-ray image of the target irradiated by heavy-ions has to be converted into an optical one.
For these purposes, the X-ray Conversion to Optical radiation and Transport (XCOT)-system was developed in the frame of a BMBF-project and commissioned in two beamtimes at the UNILAC, GSI during this work.
In experiments, we observed intense radiation of target atoms (K-shell transitions in Cu at 8–8.3 keV and L-shell transition in Ta) ionised in collisions with heavy ions as well as Doppler-shifted L-shell transitions of Au-projectiles passing through targets. This radiation can be used for monochromatic (dispersive elements like bent crystals) or polychromatic (pinhole) 2D X-ray mapping of the ion beam intensity distribution in the interaction region during the beam-target interaction. We measured the efficiency of the X-ray photon production depending on the target thickness and the number of ions passing through the target. The spatial resolution of the XCOT-system based on the multi-pinhole camera was measured to be (91±17) μm for the image magnification factor M = 2. It was considerably improved by application of a toroidally bent quartz crystal and reached 30 μm at M = 6. This resolution is optimal to image the distribution of a 1mm in diameter ion beam. As next step, the XCOT-system will be tested during the SIS18 beam-time at the HHT-experimental area.
Neutron total cross sections are an important source of experimental data in the evaluation of neutron-induced cross sections. The sum of all neutron-induced reaction cross sections can be determined with a precision of a few per cent in a relative measurement. The neutron spectrum of the photoneutron source nELBE extends in the fast region from about 100 keV to 10 MeV and has favourable conditions for transmission measurements due to the low instantaneous flux of neutrons and low gamma-flash background. Several materials of interest (in part included in the CIELO evaluation or on the HPRL of OECD/NEA) have been investigated: 197Au [1, 2], natFe [2], natW [2], 238U, natPt, 4He, natO, natNe, natXe. For gaseous targets high pressure gas cells with flat end-caps have been built that hold up to 200 bar pressure. The experimental setup will be presented including results from several transmission experiments and the data analysis leading to the total cross sections will be discussed.
Understanding the hadron spectrum is one of the primary goals of non-perturbative QCD. Many predictions have experimentally been confirmed, others still remain under experimental investigation. Of particular interest is how gluonic excitations give rise to states with constituent glue. One class of such states are hybrid mesons that are predicted by theoretical models and Lattice QCD calculations. Searching for and understanding the nature of these states is a primary physics goal of the GlueX experiment at the CEBAF accelerator at Jefferson Lab. A search for a JPC = 1−− hybrid meson candidate, the Y(2175), in φ(1020)π+π+ and φ(1020)f0(980) channels in photoproduction on a proton target has been conducted. A first measurement of non-resonant φ(1020)π+π+ and φ(1020)f0(980) total cross sections in photoproduction has been performed. An upper limit on the resonance production cross section for the Y (2175) → φ(1020)π+π+ and Y (2175) → φ(1020)f0(980) channels are estimated. Since the analysis essentially depends on the quality of the charged kaon identification, also an optimization of particle identification through an improvement of the energy loss estimation in the central drift chamber by a truncated mean method has been investigated.
This work presents, to our knowledge, the first completely passive imaging with human-body-emitted radiation in the lower THz frequency range using a broadband uncooled detector. The sensor consists of a Si CMOS field-effect transistor with an integrated log-spiral THz antenna. This THz sensor was measured to exhibit a rather flat responsivity over the 0.1–1.5-THz frequency range, with values of the optical responsivity and noise-equivalent power of around 40 mA/W and 42 pW/√Hz, respectively. These values are in good agreement with simulations which suggest an even broader flat responsivity range exceeding 2.0 THz. The successful imaging demonstratestheimpressivethermalsensitivitywhichcanbeachievedwithsuchasensor. Recording of a 2.3×7.5-cm2-sized image of the fingers of a hand with a pixel size of 1 mm2 at a scanning speed of 1 mm/s leads to a signal-to-noise ratio of 2 and a noise-equivalent temperature difference of 4.4 K. This approach shows a new sensing approach with field-effect transistors as THz detectors which are usually used for active THz detection.
Envy, the inclination to compare rewards, can be expected to unfold when inequalities in terms of pay-off differences are generated in competitive societies. It is shown that increasing levels of envy lead inevitably to a self-induced separation into a lower and an upper class. Class stratification is Nash stable and strict, with members of the same class receiving identical rewards. Upper-class agents play exclusively pure strategies, all lower-class agents the same mixed strategy. The fraction of upper-class agents decreases progressively with larger levels of envy, until a single upper-class agent is left. Numerical simulations and a complete analytic treatment of a basic reference model, the shopping trouble model, are presented. The properties of the class-stratified society are universal and only indirectly controllable through the underlying utility function, which implies that class-stratified societies are intrinsically resistant to political control. Implications for human societies are discussed. It is pointed out that the repercussions of envy are amplified when societies become increasingly competitive.
Our primary objective is to construct a plausible, unified model of inflation, dark energy and dark matter from a fundamental Lagrangian action first principle, wherein all fundamental ingredients are systematically dynamically generated starting from a very simple model of modified gravity interacting with a single scalar field employing the formalism of non-Riemannian spacetime volume-elements. The non-Riemannian volume element in the initial scalar field action leads to a hidden, nonlinear Noether symmetry which produces an energy-momentum tensor identified as the sum of a dynamically generated cosmological constant and dust-like dark matter. The non-Riemannian volume-element in the initial Einstein–Hilbert action upon passage to the physical Einstein-frame creates, dynamically, a second scalar field with a non-trivial inflationary potential and with an additional interaction with the dynamically generated dark matter. The resulting Einstein-frame action describes a fully dynamically generated inflationary model coupled to dark matter. Numerical results for observables such as the scalar power spectral index and the tensor-to-scalar ratio conform to the latest 2018 PLANCK data.
In this work a nonlinear evolution of pure states of a finite dimensional quantum system is introduced, in particular a Riccati evolution equation.
It is shown how this class of dynamics is actually a Hamiltonian dynamics in the complex projective space.
In this projective space it is shown that there is a nonlinear superposition rule, consistent with its linear counterpart in the Hilbert space. As an example, the developed nonlinear formalism is applied to the semiclassical Jaynes–Cummings model.
Later, it is shown that there is an inherent nonlinear evolution in the dynamics of the so-called generalized coherent states.
To show this, the fact that in quantum mechanics it is possible to immerse a ''classical'' manifold into the Hilbert space is employed, such that one may parametrize the time-dependence of the wave function through the variation of parameters in the classical manifold.
The immersion allows to consider the so-called principle of analogy, i.e. using the procedures and structures available from the classical setting to employ them in the quantum setting.
Finally, it is introduced the contact Hamiltonian mechanics, an extension of symplectic Hamiltonian mechanics, and it is showed that it is a natural candidate for a geometric description of non-dissipative and dissipative systems.
First, we propose a scale-invariant modified gravity interacting with a neutral scalar inflaton and a Higgs-like SU(2)×U(1) iso-doublet scalar field based on the formalism of non-Riemannian (metric-independent) spacetime volume-elements. This model describes, in the physical Einstein frame, a quintessential inflationary scenario driven by the “inflaton” together with the gravity-“inflaton” assisted dynamical spontaneous SU(2)×U(1) symmetry breaking in the post-inflationary universe, whereas the SU(2)×U(1) symmetry remains intact in the inflationary epoch. Next, we find the explicit representation of the latter quintessential inflationary model with a dynamical Higgs effect as an Eddington-type purely affine gravity.
Direct nanoscopic observation of plasma waves in the channel of a graphene field-effect transistor
(2020)
Plasma waves play an important role in many solid-state phenomena and devices. They also become significant in electronic device structures as the operation frequencies of these devices increase. A prominent example is field-effect transistors (FETs), that witness increased attention for application as rectifying detectors and mixers of electromagnetic waves at gigahertz and terahertz frequencies, where they exhibit very good sensitivity even high above the cut-off frequency defined by the carrier transit time. Transport theory predicts that the coupling of radiation at THz frequencies into the channel of an antenna-coupled FET leads to the development of a gated plasma wave, collectively involving the charge carriers of both the two-dimensional electron gas and the gate electrode. In this paper, we present the first direct visualization of these waves. Employing graphene FETs containing a buried gate electrode, we utilize near-field THz nanoscopy at room temperature to directly probe the envelope function of the electric field amplitude on the exposed graphene sheet and the neighboring antenna regions. Mapping of the field distribution documents that wave injection is unidirectional from the source side since the oscillating electrical potentials on the gate and drain are equalized by capacitive shunting. The plasma waves, excited at 2 THz, are overdamped, and their decay time lies in the range of 25-70 fs. Despite this short decay time, the decay length is rather long, i.e., 0.3-0.5 μm, because of the rather large propagation speed of the plasma waves, which is found to lie in the range of 3.5-7 × 106 m/s, in good agreement with theory. The propagation speed depends only weakly on the gate voltage swing and is consistent with the theoretically predicted 1/4 power law.
A model for the description of proton collisions from molecules composed of atoms such as hydrogen, carbon, nitrogen, oxygen and phosphorus (H, C, N, O, P) was recently extended to treat collisions with multiply charged ions with a focus on net ionization. Here we complement the work by focusing on net capture. The ion–atom collisions are computed using the two-center basis generator method. The atomic net capture cross sections are then used to assemble two models for ion–molecule collisions: An independent atom model (IAM) based on the Bragg additivity rule (labeled IAM-AR), and also the so-called pixel-counting method (IAM-PCM) which introduces dependence on the orientation of the molecule during impact. The IAM-PCM leads to significantly reduced capture cross sections relative to IAM-AR at low energies, since it takes into account the overlap of effective atomic cross sectional areas. We compare our results with available experimental and other theoretical data focusing on water vapor (H2O), methane (CH4) and uracil (C4H4N2O2). For the water molecule target we also provide results from a classical-trajectory Monte Carlo approach that includes dynamical screening effects on projectile and target. For small molecules dominated by a many-electron atom, such as carbon in methane or oxygen in water, we find a saturation phenomenon for higher projectile charges (q=3) and low energies, where the net capture cross section for the molecule is dominated by the net cross section for the many-electron atom, and the net capture cross section is not proportional to the total number of valence electrons.
Safety requirements and the need of low‐migration UV inks have received increasing attention in the packaging industry. Crucial for the development and design of low‐migration UV inkjet inks for migration‐sensitive applications is the polymerization degree. In this study, curing‐behavior of a black, high purity packaging ink (HPP‐ink) was monitored using ATR‐FTIR spectroscopy. UV irradiation of HPP‐ink led to changes in specific absorption bands of the FTIR spectra due to crosslinking reaction of double bonds. Changes in absorptions bands at 1,408 and 1,321 cm−1 permitted the determination of CC conversion of acrylic and vinyl double bond, independently of one another. In addition, a method was developed which allows the investigation of surface‐cure and deep‐cure behavior, separately.
High-quality single crystals of the unconventional superconductor NdFeAsO1 − xFx were grown. We developed a new optimized flux technique to overcome the difficulties in single-crystal growth and the sample quality limitations of NdFeAsO1 − xFx. The normal state of the F-doped samples exhibits simple metallic behavior upon cooling down from room temperature, followed by a sharp superconducting transition. The values of residual resistivity ratio (RRR) is 3.2, 6.4, and 10.3 for x = 0.1, 0.15, and 0.2, respectively. Both the large RRR and the narrow superconducting transition signpost the high quality of the crystals. We have examined the in- and out-of-plane lower critical fields, and the field at which vortices penetrate the sample of NdFeAsO1 − xFx (x = 0.1). The anisotropy ratio [γHc1 (0)] increased slightly with increasing temperature from 0.8 Tc to Tc. The temperature dependence of the first vortex penetration field was obtained under the static magnetic field, H, parallel to the c- and ab- axis, and pronounced changes in the Hc1(T) curvature were observed, which are attributed to the multi-band superconductivity.
We use a set of hadronic equations of state derived from covariant density functional theory to study the impact of their high-density behavior on the properties of rapidly rotating Δ-resonance-admixed hyperonic compact stars. In particular, we explore systematically the effects of variations of the bulk energy isoscalar skewness, Qsat, and the symmetry energy slope, Lsym, on the masses of rapidly rotating compact stars. With models for equation of state satisfying all the modern astrophysical constraints, excessively large gravitational masses of around 2.5M⊙ are only obtained under three conditions: (a) strongly attractive Δ-resonance potential in nuclear matter, (b) maximally fast (Keplerian) rotation, and (c) parameter ranges Qsat≳500 MeV and Lsym≲50 MeV. These values of Qsat and Lsym have a rather small overlap with a large sample (total of about 260) parametrizations of covariant nucleonic density functionals. The extreme nature of requirements (a)-(c) reinforces the theoretical expectation that the secondary object involved in the GW190814 event is likely to be a low-mass black hole rather than a supramassive neutron star.
Neutron capture on 241Am plays an important role in the nuclear energy production and also provides valuable information for the improvement of nuclear models and the statistical interpretation of the nuclear properties. A new experiment to measure the 241Am(n, γ) cross section in the thermal region and the first few resonances below 10 eV has been carried out at EAR2 of the n_TOF facility at CERN. Three neutron-insensitive C6D6 detectors have been used to measure the neutron-capture gamma cascade as a function of the neutron time of flight, and then deduce the neutron capture yield. Preliminary results will be presented and compared with previously obtained results at the same facility in EAR1. In EAR1 the gamma-ray background at thermal energies was about 90% of the signal while in EAR2 is up to a 25 factor much more favorable signal to noise ratio. We also extended the low energy limit down to subthermal energies. This measurement will allow a comparison with neutron capture measurements conducted at reactors and using a different experimental technique.
The hot and dense QCD matter produced in nuclear collisions at ultrarelativistic energy is characterized by very intense electromagnetic fields which attain their maximal strength in the early pre-equilibrium stage and interplay with the strong vorticity induced in the plasma by the large angular momentum of the colliding system. A promising observable keeping trace of these phenomena is the directed flow of light hadrons and heavy mesons produced in symmetric and asymmetric heavy-ion collisions as well as in proton-induced reactions. In particular, the splitting of the directed flow between particles with the same mass but opposite electric charge as a function of rapidity and transverse momentum gives access to the electromagnetic response of medium in all collision stages and in the different colliding systems. The highest influence of the electromagnetic fields is envisaged in the pre-equilibrium stage of the collision and therefore a significant imprint is left on the early-produced heavy quarks. The aim of this review is to discuss the current developments towards the understanding of the generation and relaxation time of the electromagnetic fields embedded in both large and small systems and their impact on the charge-odd directed flow of light and heavy particles, highlighting the experimental results and the different theoretical approaches. Since it is possible to perform realistic simulations of high-energy collisions that incorporate also the generated electromagnetic fields and vorticity, the study of the directed flow can provide unique insight into the early nonequilibrium phase and the ensuing QGP formation and transport properties.
In situ investigation of membrane proteins is a challenging task. Previously we demonstrated that nitroxide labels combined with pulsed ESR spectroscopy is a promising tool for this purpose. However, the nitroxide labels suffer from poor stability, high background labeling, and low sensitivity. Here we show that Finland (FTAM) and OX063 based labels enable labeling of the cobalamin transporter BtuB and BamA, the central component of the β-barrel assembly machinery (BAM) complex, in E coli. Compared to the methanethiosulfonate spin label (MTSL), trityl labels eliminated the background signals and enabled specific in situ labeling of the proteins with high efficiency. The OX063 labels show a long phase memory time (TM) of ≈5 μs. All the trityls enabled distance measurements between BtuB and an orthogonally labeled substrate with high selectivity and sensitivity down to a few μm concentration. Our data corroborate the BtuB and BamA conformations in the cellular environment of E. coli.
Activations with neutrons in the keV energy range were routinely performed at the Karlsruhe Institute of Technology (KIT) in Germany in order to simulate stellar conditions for neutron-capture cross sections. A quasi-Maxwell-Boltzmann neutron spectrum of kT = 25 keV, being of interest for the astrophysical s-process, was produced by the 7Li(p,n) reaction utilizing a 1912 keV proton beam at the Karlsruhe Van de Graaff accelerator. Activated samples resulting in long-lived nuclear reaction products with half-lives in the order of yr 100 Myr were analyzed by Accelerator Mass Spectrometry (AMS). Comparison of the obtained reaction cross sections to literature data from previous Time-of-Flight (ToF) measurements showed that the selected AMS data are systematically lower than the ToF data. To investigate this discrepancy, 54Fe(n,γ)55Fe and 35Cl(n,γ)36Cl reaction cross sections were newly measured at the Frankfurt Neutron Source (FRANZ) in Germany. To complement the existing data, an additional neutron activation of 54Fe and 35Cl at a proton energy of 2 MeV was performed. The results will give implications for the stellar environment at kT = 90 keV, reaching the not yet experimentally explored high-energy s-process range. AMS measurements of the activated samples are scheduled.
A new method of event characterization based on Deep Learning is presented. The PointNet models can be used for fast, online event-by-event impact parameter determination at the CBM experiment. For this study, UrQMD and the CBM detector simulation are used to generate Au+Au collision events at 10 AGeV which are then used to train and evaluate PointNet based architectures. The models can be trained on features like the hit position of particles in the CBM detector planes, tracks reconstructed from the hits or combinations thereof. The Deep Learning models reconstruct impact parameters from 2-14 fm with a mean error varying from -0.33 to 0.22 fm. For impact parameters in the range of 5-14 fm, a model which uses the combination of hit and track information of particles has a relative precision of 4-9% and a mean error of -0.33 to 0.13 fm. In the same range of impact parameters, a model with only track information has a relative precision of 4-10% and a mean error of -0.18 to 0.22 fm. This new method of event-classification is shown to be more accurate and less model dependent than conventional methods and can utilize the performance boost of modern GPU processor units.
This dissertation presents the development of a new radio frequency quadrupole (RFQ) structure of the 4-rod type with an operating frequency of 108 MHz for the acceleration of heavy ions with mass-to-charge ratios of up to 8.5 at high duty cycles up to CW operation ("continuous wave") at the High Charge Injector (HLI) of the GSI Helmholtz Centre for Heavy Ion Research in Darmstadt.
The need to develop a completely new RFQ for the HLI arises from the fact that with the previously designed and built 4-rod RFQ structure, which was commissioned at the HLI in 2010 as part of the planned HLI upgrade program, the desired operating modes in both pulsed and CW operation could not be achieved even after several years of operating experience and considerable efforts to eliminate or at least mitigate the severe operational instabilities. Mechanical vibrations of the electrodes, which result in strong modulated power reflection, as well as the high thermal sensitivity proved to be particularly problematic.
In addition to the RF design of the new RFQ by simulations performed with the CST Microwave Studio software, the focus of the investigations fell on the mechanical analysis of vibrations on the electrode rods caused by RF operation, for which the ANSYS Workbench software was used. Due to the high thermal load of the RFQ structure of more than 30 kW/m in CW operation, an accurate analysis of the thermal effects on electrode deformation as well as resulting frequency detuning of the resonator is also required, which was investigated by simulations within the capabilities of CST Mphysics Studio.
Based on the results of the design studies carried out by simulations and the thereby achieved design optimizations, a 4-rod RFQ prototype with 6 stems was finally manufactured, on which most of the properties expected from the simulations could be validated by measurements of the RF characteristics as well as of the vibration behavior.
Finally, based on the results of the pre-tests and considering a newly developed beam dynamics concept, a completely revised RF design for a new full-length HLI-RFQ was derived from the prototype design.
Exciting new scientific opportunities are presented for the PANDA detector at the High Energy Storage Ring in the redefined p¯¯¯p(A) collider mode, HESR-C, at the Facility for Antiproton and Ion Research (FAIR) in Europe. The high luminosity, L∼1031 cm−2 s−1, and a wide range of intermediate and high energies, sNN−−−√ up to 30 GeV for p¯¯¯p(A) collisions will allow to explore a wide range of exciting topics in QCD, including the study of the production of excited open charm and bottom states, nuclear bound states containing heavy (anti)quarks, the interplay of hard and soft physics in the dilepton production, probing short-range correlations in nuclei, and the exploration of the early, complete p¯¯¯-p- annihilation phase, where an initially pure Yang–Mills gluon plasma is formed.
This paper explores the many interesting implications for oscillator design, with optimized phase-noise performance, deriving from a newly proposed model based on the concept of oscillator conjugacy. For the case of 2-D (planar) oscillators, the model prominently predicts that only circuits producing a perfectly symmetric steady-state can have zero amplitude-to-phase (AM-PM) noise conversion, a so-called zero-state. Simulations on standard industry oscillator circuits verify all model predictions and, however, also show that these circuit classes cannot attain zero-states except in special limit-cases which are not practically relevant. Guided by the newly acquired design rules, we describe the synthesis of a novel 2-D reduced-order LC oscillator circuit which achieves several zero-states while operating at realistic output power levels. The potential future application of this developed theoretical framework for implementation of numerical algorithms aimed at optimizing oscillator phase-noise performance is briefly discussed.
The structure and flexibility of RNA depends sensitively on the microenvironment. Using pulsed electron-electron double-resonance (PELDOR)/double electron-electron resonance (DEER) spectroscopy combined with advanced labeling techniques, we show that the structure of double-stranded RNA (dsRNA) changes upon internalization into Xenopus lævis oocytes. Compared to dilute solution, the dsRNA A-helix is more compact in cells. We recapitulate this compaction in a densely crowded protein solution. Atomic-resolution molecular dynamics simulations of dsRNA semi-quantitatively capture the compaction, and identify non-specific electrostatic interactions between proteins and dsRNA as a possible driver of this effect.
We estimate the temperature dependence of the bulk viscosity in a relativistic hadron gas. Employing the Green–Kubo formalism in the SMASH (Simulating Many Accelerated Strongly-interacting Hadrons) transport approach, we study different hadronic systems in increasing order of complexity. We analyze the (in)validity of the single exponential relaxation ansatz for the bulk-channel correlation function and the strong influence of the resonances and their lifetimes. We discuss the difference between the inclusive bulk viscosity of an equilibrated, long-lived system, and the effective bulk viscosity of a short-lived mixture like the hadronic phase of relativistic heavy-ion collisions, where the processes whose inverse relaxation rate are larger than the fireball duration are excluded from the analysis. This clarifies the differences between previous approaches which computed the bulk viscosity including/excluding the very slow processes in the hadron gas. We compare our final results with previous hadron gas calculations and confirm a decreasing trend of the inclusive bulk viscosity over entropy density as temperature increases, whereas the effective bulk viscosity to entropy ratio, while being lower than the inclusive one, shows no strong dependence to temperature.
Stored and cooled highly-charged ions offer unprecedented capabilities for precision studies in realm of atomic-, nuclear-structure and astrophysics. In context of the latter, after the successful investigation of the cross section of 96Ru(p,γ) in 2009, in 2016 the first measurement of the 124Xe(p,γ)125Cs reaction was performed at the Experimental Storage Ring (ESR) at GSI.
We study the influence of the baryon chemical potential μB on the properties of the Quark–Gluon–Plasma (QGP) in and out-of equilibrium. The description of the QGP in equilibrium is based on the effective propagators and couplings from the Dynamical QuasiParticle Model (DQPM) that is matched to reproduce the equation-of-state of the partonic system above the deconfinement temperature Tc from lattice Quantum Chromodynamics (QCD). We study the transport coefficients such as the ratio of shear viscosity η and bulk viscosity ζ over entropy density s, i.e., η/s and ζ/s in the (T,μ) plane and compare to other model results available at μB=0 . The out-of equilibrium study of the QGP is performed within the Parton–Hadron–String Dynamics (PHSD) transport approach extended in the partonic sector by explicitly calculating the total and differential partonic scattering cross sections based on the DQPM and the evaluated at actual temperature T and baryon chemical potential μB in each individual space-time cell where partonic scattering takes place. The traces of their μB dependences are investigated in different observables for symmetric Au + Au and asymmetric Cu + Au collisions such as rapidity and mT -distributions and directed and elliptic flow coefficients v1,v2 in the energy range 7.7 GeV ≤sNN−−−−√≤200 GeV.
We derive the relation between cumulants of a conserved charge measured in a subvolume of a thermal system and the corresponding grand-canonical susceptibilities, taking into account exact global conservation of that charge. The derivation is presented for an arbitrary equation of state, with the assumption that the subvolume is sufficiently large to be close to the thermodynamic limit. Our framework – the subensemble acceptance method (SAM) – quantifies the effect of global conservation laws and is an important step toward a direct comparison between cumulants of conserved charges measured in central heavy ion collisions and theoretical calculations of grand-canonical susceptibilities, such as lattice QCD. As an example, we apply our formalism to net-baryon fluctuations at vanishing baryon chemical potentials as encountered in collisions at the LHC and RHIC.
In the past two decades, pions created in the high density regions of heavy ion collisions have been predicted to be sensitive at high densities to the symmetry energy term in the nuclear equation of state, a property that is key to our understanding of neutron stars. In a new experiment designed to study the symmetry energy, the multiplicities of negatively and positively charged pions have been measured with high accuracy for central 132Sn+124Sn, 112Sn+124Sn, and 108Sn+112Sn collisions at E/A = 270 MeV with the SπRIT Time Projection Chamber. While individual pion multiplicities are measured to 4% accuracy, those of the charged pion multiplicity ratios are measured to 2% accuracy. We compare these data to predictions from seven major transport models. The calculations reproduce qualitatively the dependence of the multiplicities and their ratios on the total neutron and proton number in the colliding systems. However, the predictions of the transport models from different codes differ too much to allow extraction of reliable constraints on the symmetry energy from the data. This finding may explain previous contradictory conclusions on symmetry energy constraints obtained from pion data in Au+Au system. These new results call for still better understanding of the differences among transport codes, and new observables that are more sensitive to the density dependence of the symmetry energy.
The production of Ξ(1321)− and Ξ¯¯¯¯(1321)+ hyperons in inelastic p+p interactions is studied in a fixed target experiment at a beam momentum of 158 GeV/c. Double differential distributions in rapidity y and transverse momentum pT are obtained from a sample of 33M inelastic events. They allow to extrapolate the spectra to full phase space and to determine the mean multiplicity of both Ξ− and Ξ¯¯¯¯+. The rapidity and transverse momentum spectra are compared to transport model predictions. The Ξ− mean multiplicity in inelastic p+p interactions at 158 GeV/c is used to quantify the strangeness enhancement in A+A collisions at the same centre-of-mass energy per nucleon pair.
A measurement of charged hadron pair correlations in two-dimensional ηφ space is presented. The analysis is based on total 30 million central Be + Be collisions observed in the NA61/SHINE detector at the CERN SPS for incident beam momenta of 19A, 30A, 40A, 75A, and 150A GeV/c. Measurements were carried out for unlike-sign and like-sign charge hadron pairs independently. The C(η, φ) correlation functions were compared with results from a similar analysis on p + p interactions at similar beam momenta per nucleon. General trends of the backto-back correlations are similar in central Be + Be collisions and p + p interactions, but are suppressed in magnitude due to the increased combinatorial background. Predictions from the Epos and UrQMD models are compared to the measurements. Evolution of an enhancement around (η, φ) = (0, 0) with incident energy is observed in central Be + Be collisions. It is not predicted by both models and almost non-existing in proton–proton collisions at the same momentum per nucleon.
An incoming or outgoing hadron in a hard collision with large momentum transfer gets squeezed in the transverse direction to its momentum. In the case of nuclear targets, this leads to the reduced interaction of such hadrons with surrounding nucleons which is known as color transparency (CT). The identification of CT in exclusive processes on nuclear targets is of significant interest not only by itself but also due to the fact that CT is a necessary condition for the applicability of factorization for the description of the corresponding elementary process. In this paper we discuss the semiexclusive processes A(e,e′π+) , A(π−,l−l+) and A(γ,π−p) . Since CT is closely related to hadron formation mechanism, the reduced interaction of ’pre-hadrons’ with nucleons is a common feature of generic high-energy inclusive processes on nuclear targets, such as hadron attenuation in deep inelastic scattering (DIS). We will discuss the novel way to study hadron formation via slow neutron production induced by a hard photon interaction with a nucleus. Finally, the opportunity to study hadron formation effects in heavy-ion collisions in the NICA regime will be considered.
We construct a new equation of state for the baryonic matter under an intense magnetic field within the framework of covariant density functional theory. The composition of matter includes hyperons as well as Δ-resonances. The extension of the nucleonic functional to the hypernuclear sector is constrained by the experimental data on Λ and Ξ-hypernuclei. We find that the equation of state stiffens with the inclusion of the magnetic field, which increases the maximum mass of neutron star compared to the non-magnetic case. In addition, the strangeness fraction in the matter is enhanced. Several observables, like the Dirac effective mass, particle abundances, etc. show typical oscillatory behavior as a function of the magnetic field and/or density which is traced back to the occupation pattern of Landau levels.
J/ψ production as a function of charged-particle multiplicity in p-Pb collisions at √sNN = 8.16 TeV
(2020)
Inclusive J/ψ yields and average transverse momenta in p-Pb collisions at a center-of-mass energy per nucleon pair s NN $$ \sqrt{s_{\mathrm{NN}}} $$ = 8.16 TeV are measured as a function of the charged-particle pseudorapidity density with ALICE. The J/ψ mesons are reconstructed at forward (2.03 < y cms < 3.53) and backward (−4.46 < y cms < −2.96) center-of-mass rapidity in their dimuon decay channel while the charged-particle pseudorapidity density is measured around midrapidity. The J/ψ yields at forward and backward rapidity normalized to their respective average values increase with the normalized charged-particle pseudorapidity density, the former showing a weaker increase than the latter. The normalized average transverse momenta at forward and backward rapidity manifest a steady increase from low to high charged-particle pseudorapidity density with a saturation beyond the average value.
This paper presents the measurements of π±, K±, p and p¯¯¯ transverse momentum (pT) spectra as a function of charged-particle multiplicity density in proton–proton (pp) collisions at s√ = 13 TeV with the ALICE detector at the LHC. Such study allows us to isolate the center-of-mass energy dependence of light-flavour particle production. The measurements reported here cover a pT range from 0.1 to 20 GeV/c and are done in the rapidity interval |y|<0.5. The pT-differential particle ratios exhibit an evolution with multiplicity, similar to that observed in pp collisions at s√ = 7 TeV, which is qualitatively described by some of the hydrodynamical and pQCD-inspired models discussed in this paper. Furthermore, the pT-integrated hadron-to-pion yield ratios measured in pp collisions at two different center-of-mass energies are consistent when compared at similar multiplicities. This also extends to strange and multi-strange hadrons, suggesting that, at LHC energies, particle hadrochemistry scales with particle multiplicity the same way under different collision energies and colliding systems.
Coherent photoproduction of ρ0 vector mesons in ultra-peripheral Pb-Pb collisions at √sNN = 5.02 TeV
(2020)
Cross sections for the coherent photoproduction of ρ0 vector mesons in ultra-peripheral Pb-Pb collisions at sNN−−−√ = 5.02 TeV are reported. The measurements, which rely on the π+π− decay channel, are presented in three regions of rapidity covering the range |y| < 0.8. For each rapidity interval, cross sections are shown for different nuclear-breakup classes defined according to the presence of neutrons measured in the zero-degree calorimeters. The results are compared with predictions based on different models of nuclear shadowing. Finally, the observation of a coherently produced resonance-like structure with a mass around 1.7 GeV/c2 and a width of about 140 MeV/c2 is reported and compared with similar observations from other experiments.
The measurement of the azimuthal-correlation function of prompt D mesons with charged particles in pp collisions at s√=5.02 TeV and p–Pb collisions at sNN−−−√=5.02 TeV with the ALICE detector at the LHC is reported. The D0, D+, and D∗+ mesons, together with their charge conjugates, were reconstructed at midrapidity in the transverse momentum interval 3<pT<24 GeV/c and correlated with charged particles having pT>0.3 GeV/c and pseudorapidity |η|<0.8. The properties of the correlation peaks appearing in the near- and away-side regions (for Δφ≈0 and Δφ≈π, respectively) were extracted via a fit to the azimuthal correlation functions. The shape of the correlation functions and the near- and away-side peak features are found to be consistent in pp and p–Pb collisions, showing no modifications due to nuclear effects within uncertainties. The results are compared with predictions from Monte Carlo simulations performed with the PYTHIA, POWHEG+PYTHIA, HERWIG, and EPOS 3 event generators.
The inclusive J/ψ production in Pb–Pb collisions at the center-of-mass energy per nucleon pair sNN−−−√ = 5.02 TeV, measured with the ALICE detector at the CERN LHC, is reported. The J/ψ meson is reconstructed via the dimuon decay channel at forward rapidity (2.5 < y < 4) down to zero transverse momentum. The suppression of the J/ψ yield in Pb–Pb collisions with respect to binary-scaled pp collisions is quantified by the nuclear modification factor (RAA). The RAA at sNN−−−√ = 5.02 TeV is presented and compared with previous measurements at sNN−−−√ = 2.76 TeV as a function of the centrality of the collision, and of the J/ψ transverse momentum and rapidity. The inclusive J/ψ RAA shows a suppression increasing toward higher transverse momentum, with a steeper dependence for central collisions. The modification of the J/ψ average transverse momentum and average squared transverse momentum is also studied. Comparisons with the results of models based on a transport equation and on statistical hadronization are carried out.
Z-boson production in p-Pb collisions at √sNN = 8.16 TeV and Pb-Pb collisions at √sNN = 5.02 TeV
(2020)
Measurement of Z-boson production in p-Pb collisions at sNN−−−√ = 8.16 TeV and Pb-Pb collisions at sNN−−−√ = 5.02 TeV is reported. It is performed in the dimuon decay channel, through the detection of muons with pseudorapidity −4 < ημ < −2.5 and transverse momentum pμT > 20 GeV/c in the laboratory frame. The invariant yield and nuclear modification factor are measured for opposite-sign dimuons with invariant mass 60 < mμμ < 120 GeV/c2 and rapidity 2.5 < yμμcms < 4. They are presented as a function of rapidity and, for the Pb-Pb collisions, of centrality as well. The results are compared with theoretical calculations, both with and without nuclear modifications to the Parton Distribution Functions (PDFs). In p-Pb collisions the center-of-mass frame is boosted with respect to the laboratory frame, and the measurements cover the backward (−4.46 < yμμcms < −2.96) and forward (2.03 < yμμcms < 3.53) rapidity regions. For the p-Pb collisions, the results are consistent within experimental and theoretical uncertainties with calculations that include both free-nucleon and nuclear-modified PDFs. For the Pb-Pb collisions, a 3.4σ deviation is seen in the integrated yield between the data and calculations based on the free-nucleon PDFs, while good agreement is found once nuclear modifications are considered.
The production rates and the transverse momentum distribution of strange hadrons at mid-rapidity (|y|<0.5) are measured in proton-proton collisions at s√ = 13 TeV as a function of the charged particle multiplicity, using the ALICE detector at the LHC. The production rates of K0S, Λ, Ξ, and Ω increase with the multiplicity faster than what is reported for inclusive charged particles. The increase is found to be more pronounced for hadrons with a larger strangeness content. Possible auto-correlations between the charged particles and the strange hadrons are evaluated by measuring the event-activity with charged particle multiplicity estimators covering different pseudorapidity regions. When comparing to lower energy results, the yields of strange hadrons are found to depend only on the mid-rapidity charged particle multiplicity. Several features of the data are reproduced qualitatively by general purpose QCD Monte Carlo models that take into account the effect of densely-packed QCD strings in high multiplicity collisions. However, none of the tested models reproduce the data quantitatively. This work corroborates and extends the ALICE findings on strangeness production in proton-proton collisions at 7 TeV.
The pT-differential non-linear flow modes, v4,22, v5,32, v6,33 and v6,222 for π±, K±, K0S , p + p¯¯¯, Λ + Λ¯¯¯¯ and ϕ-meson have been measured for the first time at sNN−−−√ = 5.02 TeV in Pb-Pb collisions with the ALICE detector at the Large Hadron Collider. The results were obtained with a multi-particle technique, correlating the identified hadrons with reference charged particles from a different pseudorapidity region. These non-linear observables probe the contribution from the second and third order initial spatial anisotropy coefficients to higher flow harmonics. All the characteristic features observed in previous pT-differential anisotropic flow measurements for various particle species are also present in the non-linear flow modes, i.e. increase of magnitude with increasing centrality percentile, mass ordering at low pT and particle type grouping in the intermediate pT range. Hydrodynamical calculations (iEBE-VISHNU) that use different initial conditions and values of shear and bulk viscosity to entropy density ratios are confronted with the data at low transverse momenta. These calculations exhibit a better agreement with the anisotropic flow coefficients than the non-linear flow modes. These observations indicate that non-linear flow modes can provide additional discriminatory power in the study of initial conditions as well as new stringent constraints to hydrodynamical calculations.
The multiplicity dependence of electron production from heavy-flavour hadron decays as a function of transverse momentum was measured in p-Pb collisions at sNN−−−√ = 5.02 TeV using the ALICE detector at the LHC. The measurement was performed in the centre-of-mass rapidity interval −1.07 < ycms < 0.14 and transverse momentum interval 2 < pT < 16 GeV/c. The multiplicity dependence of the production of electrons from heavy-flavour hadron decays was studied by comparing the pT spectra measured for different multiplicity classes with those measured in pp collisions (QpPb) and in peripheral p-Pb collisions (Qcp). The QpPb results obtained are consistent with unity within uncertainties in the measured pT interval and event classes. This indicates that heavy-flavour decay electron production is consistent with binary scaling and independent of the geometry of the collision system. Additionally, the results suggest that cold nuclear matter effects are negligible within uncertainties, in the production of heavy-flavour decay electrons at midrapidity in p-Pb collisions.
Experimental results are presented on event-by-event net-proton fluctuation measurements in Pb–Pb collisions at √sNN = 2.76 TeV, recorded by the ALICE detector at the CERN LHC. These measurements have as their ultimate goal an experimental test of Lattice QCD (LQCD) predictions on second and higher order cumulants of net-baryon distributions to search for critical behavior near the QCD phase boundary. Before confronting them with LQCD predictions, account has to be taken of correlations stemming from baryon number conservation as well as fluctuations of participating nucleons. Both effects influence the experimental measurements and are usually not considered in theoretical calculations. For the first time, it is shown that event-by-event baryon number conservation leads to subtle long-range correlations arising from very early interactions in the collisions.
Thermal leptogenesis, in the framework of the standard model with three additional heavy Majorana neutrinos, provides an attractive scenario to explain the observed baryon asymmetry in the universe. It is based on the out-of-equilibrium decay of Majorana neutrinos in a thermal bath of standard model particles, which in a fully quantum field theoretical formalism is obtained by solving Kadanoff-Baym equations. So far, the leading two-loop contributions from leptons and Higgs particles are included, but not yet gauge corrections. These enter at three-loop level but, in certain kinematical regimes, require a resummation to infinite loop order for a result to leading order in the gauge coupling. In this work, we apply such a resummation to the calculation of the lepton number density. The full result for the simplest “vanilla leptogenesis” scenario is by O(1) increased compared to that of quantum Boltzmann equations, and for the first time permits an estimate of all theoretical uncertainties. This step completes the quantum theory of leptogenesis and forms the basis for quantitative evaluations, as well as extensions to other scenarios.
This article reports measurements characterizing the Underlying Event (UE) associated with hard scatterings at midrapidity (|η| < 0.8) in pp collisions at s√ = 13 TeV. The hard scatterings are identified by the leading particle, the charged particle with the highest transverse momentum (pleadingT) in the event. Charged-particle number-densities and summed transverse-momentum densities are measured in different azimuthal regions defined with respect to the leading particle direction: Toward, Transverse, and Away. The Toward and Away regions contain the fragmentation products of the hard scatterings in addition to the UE contribution, whereas particles in the Transverse region are expected to originate predominantly from the UE. The study is performed as a function of pleadingT with three different pT thresholds for the associated particles, ptrackT > 0.15, 0.5, and 1.0 GeV/c. The charged-particle density in the Transverse region rises steeply for low values of pleadingT and reaches a plateau. The results confirm the trend that the charged-particle density in the Transverse region shows a stronger increase with s√ than the inclusive charged-particle density at midrapidity. The UE activity is increased by approximately 20% when going from 7 TeV to 13 TeV pp collisions. The plateau in the Transverse region (5 <pleadingT< 40 GeV/c) is further characterized by the probability distribution of its charged-particle multiplicity normalized to its average value (relative transverse activity, RT) and the mean transverse momentum as a function of RT. Experimental results are compared to model calculations using PYTHIA 8 and EPOS LHC. The overall agreement between models and data is within 30%. These measurements provide new insights on the interplay between hard scatterings and the associated UE in pp collisions.
The inclusive J/ψ elliptic (v2) and triangular (v3) flow coefficients measured at forward rapidity (2.5 < y < 4) and the v2 measured at midrapidity (|y| < 0.9) in Pb-Pb collisions at sNN−−−√ = 5.02 TeV using the ALICE detector at the LHC are reported. The entire Pb-Pb data sample collected during Run 2 is employed, amounting to an integrated luminosity of 750 μb−1 at forward rapidity and 93 μb−1 at midrapidity. The results are obtained using the scalar product method and are reported as a function of transverse momentum pT and collision centrality. At midrapidity, the J/ψ v2 is in agreement with the forward rapidity measurement. The centrality averaged results indicate a positive J/ψ v3 with a significance of more than 5σ at forward rapidity in the pT range 2 < pT < 5 GeV/c. The forward rapidity v2, v3, and v3/v2 results at low and intermediate pT (pT ≲ 8 GeV/c) exhibit a mass hierarchy when compared to pions and D mesons, while converging into a species-independent curve at higher pT. At low and intermediate pT, the results could be interpreted in terms of a later thermalization of charm quarks compared to light quarks, while at high pT, path-length dependent effects seem to dominate. The J/ψ v2 measurements are further compared to a microscopic transport model calculation. Using a simplified extension of the quark scaling approach involving both light and charm quark flow components, it is shown that the D-meson vn measurements can be described based on those for charged pions and J/ψ flow.
The invariant differential cross section of inclusive ω(782) meson production at midrapidity (|y|<0.5) in pp collisions at s√=7TeV was measured with the ALICE detector at the LHC over a transverse momentum range of 2<pT<17GeV/c. The ω meson was reconstructed via its ω→π+π−π0 decay channel. The measured ω production cross section is compared to various calculations: PYTHIA 8.2 Monash 2013 describes the data, while PYTHIA 8.2 Tune 4C overestimates the data by about 50%. A recent NLO calculation, which includes a model describing the fragmentation of the whole vector-meson nonet, describes the data within uncertainties below 6GeV/c, while it overestimates the data by up to 50% for higher pT. The ω/π0 ratio is in agreement with previous measurements at lower collision energies and the PYTHIA calculations. In addition, the measurement is compatible with transverse mass scaling within the measured pT range and the ratio is constant with Cω/π0=0.67±0.03~(stat)~±0.04~(sys)~ above a transverse momentum of 2.5GeV/c.
Systematic studies of charge-dependent two- and three-particle correlations in Pb-Pb collisions at sNN−−−√ = 2.76 and 5.02 TeV used to probe the Chiral Magnetic Effect (CME) are presented. These measurements are performed for charged particles in the pseudorapidity (η) and transverse momentum (pT) ranges |η| < 0.8 and 0.2 < pT < 5 GeV/c. A significant charge-dependent signal that becomes more pronounced for peripheral collisions is reported for the CME-sensitive correlators γ1, 1 = 〈cos(φα + φβ − 2Ψ2)〉 and γ1, − 3 = 〈cos(φα − 3φβ + 2Ψ2)〉. The results are used to estimate the contribution of background effects, associated with local charge conservation coupled to anisotropic flow modulations, to measurements of the CME. A blast-wave parametrisation that incorporates local charge conservation tuned to reproduce the centrality dependent background effects is not able to fully describe the measured γ1,1. Finally, the charge and centrality dependence of mixed-harmonics three-particle correlations, of the form γ1, 2 = 〈cos(φα + 2φβ − 3Ψ3)〉, which are insensitive to the CME signal, verify again that background contributions dominate the measurement of γ1,1.
The elliptic and triangular flow coefficients v2 and v3 of prompt D0, D+, and D∗+ mesons were measured at midrapidity (|y| < 0.8) in Pb–Pb collisions at the centre-of-mass energy per nucleon pair of √sNN = 5.02 TeV with the ALICE detector at the LHC. The D mesons were reconstructed via their hadronic decays in the transverse momentum interval 1 < pT < 36 GeV/c in central (0–10%) and semi-central (30–50%) collisions. Compared to pions, protons, and J/ψ mesons, the average D-meson vn harmonics are compatible within uncertainties with a mass hierarchy for pT 3 GeV/c, and are similar to those of charged pions for higher pT. The coupling of the charm quark to the light quarks in the underlying medium is further investigated with the application of the event-shape engineering (ESE) technique to the D-meson v2 and pT-differential yields. The D-meson v2 is correlated with average bulk elliptic flow in both central and semi-central collisions. Within the current precision, the ratios of per-event Dmeson yields in the ESE-selected and unbiased samples are found to be compatible with unity. All the measurements are found to be reasonably well described by theoretical calculations including the effects of charm-quark transport and the recombination of charm quarks with light quarks in a hydrodynamically expanding medium.
The study of (anti-)deuteron production in pp collisions has proven to be a powerful tool to investigate the formation mechanism of loosely bound states in high-energy hadronic collisions. In this paper the production of (anti-)deuterons is studied as a function of the charged particle multiplicity in inelastic pp collisions at s√=13 TeV using the ALICE experiment. Thanks to the large number of accumulated minimum bias events, it has been possible to measure (anti-)deuteron production in pp collisions up to the same charged particle multiplicity (dNch/dη∼26) as measured in p–Pb collisions at similar centre-of-mass energies. Within the uncertainties, the deuteron yield in pp collisions resembles the one in p–Pb interactions, suggesting a common formation mechanism behind the production of light nuclei in hadronic interactions. In this context the measurements are compared with the expectations of coalescence and statistical hadronisation models (SHM).
In the last two decades, new unpredicted charmonium-like states with extraordinary characteristics have been observed experimentally. These states also known as the XYZ states, e.g., the Y(4260) or the X(3872), are mostly interpreted as QCD allowed exotic hadrons. One of the leading hadron physics experiments in the world, the Beijing Electron Spectrometer III (BESIII) at the Beijing Electron-Positron Collider II (BEPCII) is aiming towards revealing the internal structure of these states. It has brought numerous breakthrough discoveries including the discovery of the charged Zc(3900). In order to understand the nature of the Y(4260) state and its decay patterns, an inclusive analysis is performed for different recoil systems (π+π−,K+K− and K±π∓) using the BESIII data samples for center of mass energies above 4 GeV collected between 2013 and 2019. The aim of this analysis is twofold: on one hand, we search for new unobserved charmonium-like decay channels using the missing mass technique and on the other hand, it provides an accurate inclusive cross section measurement for e+e−→X π+π−, with the X being the J/ψ, hc and ψ(2S), respectively. Two resonant structures, the Y(4220) and the Y(4390), are observed in the inclusive energy dependent Born cross section of e+e−→hc π+π−, which is consistent with the BESIII exclusive measurements. Moreover, the energy dependent cross section of e+e−→J/ψ π+π− is investigated, in which two resonances have consistently been observed with the previous BESIII exclusive studies, namely, the Y(4220) and the Y(4320). In the (K±π±) recoil system, possible Y(4260) open charm decay channels are investigated. Two enhancements are observed in the inclusive energy dependent cross section of e+e−→DD above 4.13GeV, which could possibly be the ψ(4160)and the ψ(4415).
Although the 12C(n,p)12B and 12C(n,d)11B reactions are of interest in several fields of basic and applied Nuclear Physics the present knowledge of these two cross-sections is far from being accurate and reliable, with both evaluations and data showing sizable discrepancies. As part of the challenging n_TOF program on (n,cp) nuclear reactions study, the energy differential cross-sections of the 12C(n,p)12B and 12C(n,d)11 B reactions have been measured at CERN from the reaction thresholds up to 30 MeV neutron energy. Both measurements have been recently performed at the long flight-path (185 m) experimental area of the n_TOF facility at CERN using a pure (99.95%) rigid graphite target and two silicon telescopes. In this paper an overview of the experiment is presented together with a few preliminary results.
The differential invariant yield as a function of transverse momentum (pT) of electrons from semileptonic heavy-flavour hadron decays was measured at midrapidity in central (0–10%), semi-central (30–50%) and peripheral (60–80%) lead–lead (Pb–Pb) collisions at √sNN = 5.02 TeV in the pT intervals 0.5–26 GeV/c (0–10% and 30–50%) and 0.5–10 GeV/c (60–80%). The production cross section in proton–proton (pp) collisions at √s = 5.02 TeV was measured as well in 0.5 < pT < 10 GeV/c and it lies close to the upper band of perturbative QCD calculation uncertainties up to pT = 5 GeV/c and close to the mean value for larger pT. The modification of the electron yield with respect to what is expected for an incoherent superposition of nucleon–nucleon collisions is evaluated by measuring the nuclear modification factor RAA. The measurement of the RAA in different centrality classes allows in-medium energy loss of charm and beauty quarks to be investigated. The RAA shows a suppression with respect to unity at intermediate pT, which increases while moving towards more central collisions. Moreover, the measured RAA is sensitive to the modification of the parton distribution functions (PDF) in nuclei, like nuclear shadowing, which causes a suppression of the heavy-quark production at low pT in heavy-ion collisions at LHC.
Inclusive ψ(2S) production is measured in p-Pb collisions at the centre-of-mass energy per nucleon-nucleon pair sNN−−−√ = 8.16 TeV, using the ALICE detector at the CERN LHC. The production of ψ(2S) is studied at forward (2.03 < ycms < 3.53) and backward (−4.46 < ycms < −2.96) centre-of-mass rapidity and for transverse momentum pT < 12 GeV/c via the decay to muon pairs. In this paper, we report the integrated as well as the ycms- and pT-differential inclusive production cross sections. Nuclear effects on ψ(2S) production are studied via the determination of the nuclear modification factor that shows a strong suppression at both forward and backward centre-of-mass rapidities. Comparisons with corresponding results for inclusive J/ψ show a similar suppression for the two states at forward rapidity (p-going direction), but a stronger suppression for ψ(2S) at backward rapidity (Pb-going direction). As a function of pT, no clear dependence of the nuclear modification factor is found. The relative size of nuclear effects on ψ(2S) production compared to J/ψ is also studied via the double ratio of production cross sections [σψ(2S)/σJ/ψ]pPb/[σψ(2S)/σJ/ψ]pp between p-Pb and pp collisions. The results are compared with theoretical models that include various effects related to the initial and final state of the collision system and also with previous measurements at sNN−−−√ = 5.02 TeV.
The production of the Λ(1520) baryonic resonance has been measured at midrapidity in inelastic pp collisions at s√=7 TeV and in p–Pb collisions at sNN−−−√=5.02 TeV for non-single diffractive events and in multiplicity classes. The resonance is reconstructed through its hadronic decay channel Λ(1520) →pK− and the charge conjugate with the ALICE detector. The integrated yields and mean transverse momenta are calculated from the measured transverse momentum distributions in pp and p–Pb collisions. The mean transverse momenta follow mass ordering as previously observed for other hyperons in the same collision systems. A Blast-Wave function constrained by other light hadrons (π, K, K0S, p, Λ) describes the shape of the Λ(1520) transverse momentum distribution up to 3.5 GeV/c in p–Pb collisions. In the framework of this model, this observation suggests that the Λ(1520) resonance participates in the same collective radial flow as other light hadrons. The ratio of the yield of Λ(1520) to the yield of the ground state particle Λ remains constant as a function of charged-particle multiplicity, suggesting that there is no net effect of the hadronic phase in p–Pb collisions on the Λ(1520) yield.
Diese Thesis befasst sich mit dem Problem korrelierter Elektronensysteme in realen Materialien. Ausgangspunkt hierbei ist die quantenmechanische Beschreibung dieser Systeme im Rahmen der sogenannten Kohn-Scham Dichtefunktionaltheorie, welche die Elektronen der Kristallsysteme als effektiv nicht-wechselwirkende Teilchen beschreibt.
Während diese Modellierung im Falle vieler Materialklassen erfolgreich ist, unterscheiden sich die korrelierten Elektronensysteme dadurch, dass der kollektive Charakter der Elektronendynamik nicht zu vernachlässigen ist.
Um diese Korrelationseffekte genauer zu untersuchen, verwenden wir in dieser Arbeit das Hubbard-Modell, welches mit der projektiven Wannierfunktionsmethode aus der Kohn-Scham Dichtefunktionaltheorie konstruiert werden kann.
Das Hubbard-Modell umfasst hierbei nur die lokale Elektron-Elektron-Wechselwirkung auf einem Gitter. Auch wenn das Modell augenscheinlich sehr simpel ist, existieren exakte Lösungen nur in bestimmten Grenzfällen. Dies macht die Entwicklung approximativer Ansätze erforderlich, wobei die Weiterentwicklung der sogenannten Two-Particle Self-Consistent Methode (TPSC) eine zentrale Rolle dieser Arbeit einnimmt.
Bei TPSC handelt es sich um eine Vielteilchenmethode, die in der Sprache funktionaler Ableitungen und sogenannter conserving approximations hergeleitet werden kann.
Der zentrale Gedanke dabei ist, den effektiven Wechselwirkungsvertex als statisch und lokal zu approximieren. Dies wiederum erlaubt die Bewegungsgleichung des Systems
erheblich zu vereinfachen, sodass eine numerische approximative Lösung des Hubbard-Modells möglich wird. Vorsetzung hierbei ist nur, dass sich das System in der normalleitenden Phase befindet und die bei Phasenübergängen entstehenden Fluktuationen nicht zu groß sind.
Während diese Methode ursprünglich von Y. M. Vilk und A.-M. Tremblay für das Ein-Orbital Hubbard-Modell entwickelt wurde, stellen wir in dieser Arbeit eine Erweiterung auf Viel-Orbital-Systeme vor.
Im Falle mehrerer Orbitale treten in der TPSC-Herleitung einzelne Komplikationen auf, die mit weiteren Approximationen behandelt werden müssen. Diese werden anhand eines einfachen Zwei-Orbital Modell-Systems diskutiert und die TPSC-Ergebnisse werden darüber hinaus mit den Ergebnissen der etablierten dynamischen Molekularfeldnährung verglichen.
In diesem Zusammenhang werden auch mögliche zukünftige Erweiterungen bzw. Verbesserungen von TPSC diskutiert.
Ein weiterer wichtiger Aspekt ist die Anwendung von TPSC auf reale Materialien.
In diesem Zusammenhang werden in dieser Arbeit die supraleitenden Eigenschaften der organischen K-(ET)2X Systeme untersucht. Hierbei lassen die TPSC-Resultate darauf schließen, dass das populäre Dimer-Modell, welches zur Beschreibung dieser Materialien herangezogen wird, nicht genügt um die experimentell bestimmten kritischen Temperaturen zu erklären und dass das komplexere Molekülmodell weitere exotische supraleitende Lösungen zulässt.
Schließlich untersuchen wir außerdem die elektronischen Eigenschaften des eisenbasierten Supraleiters LiFeAs und diskutieren inwieweit nicht-lokale Korrelationseffekte, welche durch TPSC aufgelöst werden können, die experimentellen Daten reproduzieren.
The spike protein (S) of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is required for cell entry and is the primary focus for vaccine development. In this study, we combined cryo–electron tomography, subtomogram averaging, and molecular dynamics simulations to structurally analyze S in situ. Compared with the recombinant S, the viral S was more heavily glycosylated and occurred mostly in the closed prefusion conformation. We show that the stalk domain of S contains three hinges, giving the head unexpected orientational freedom. We propose that the hinges allow S to scan the host cell surface, shielded from antibodies by an extensive glycan coat. The structure of native S contributes to our understanding of SARS-CoV-2 infection and potentially to the development of safe vaccines.
We analyze the behavior of cumulants of conserved charges in a subvolume of a thermal system with exact global conservation laws by extending a recently developed subensemble acceptance method (SAM) [1] to multiple conserved charges. Explicit expressions for all diagonal and off-diagonal cumulants up to sixth order that relate them to the grand canonical susceptibilities are obtained. The derivation is presented for an arbitrary equation of state with an arbitrary number of different conserved charges. The global conservation effects cancel out in any ratio of two second order cumulants, in any ratio of two third order cumulants, as well as in a ratio of strongly intensive measures Σ and ∆ involving any two conserved charges, making all these quantities particularly suitable for theory-to-experiment comparisons in heavy-ion collisions. We also show that the same cancellation occurs in correlators of a conserved charge, like the electric charge, with any non-conserved quantity such as net proton or net kaon number. The main results of the SAM are illustrated in the framework of the hadron resonance gas model. We also elucidate how net-proton and net-Λ fluctuations are affected by conservation of electric charge and strangeness in addition to baryon number.
The production of the Λ(1520) baryonic resonance has been measured at midrapidity in inelastic pp collisions at s√ = 7 TeV and in p-Pb collisions at sNN−−−√ = 5.02 TeV for non-single diffractive events and in multiplicity classes. The resonance is reconstructed through its hadronic decay channel Λ(1520) → pK− and the charge conjugate with the ALICE detector. The integrated yields and mean transverse momenta are calculated from the measured transverse momentum distributions in pp and p-Pb collisions. The mean transverse momenta follow mass ordering as previously observed for other hyperons in the same collision systems. A Blast-Wave function constrained by other light hadrons (π, K, K0S, p, Λ) describes the shape of the Λ(1520) transverse momentum distribution up to 3.5 GeV/c in p-Pb collisions. In the framework of this model, this observation suggests that the Λ(1520) resonance participates in the same collective radial flow as other light hadrons. The ratio of the yield of Λ(1520) to the yield of the ground state particle Λ remains constant as a function of charged-particle multiplicity, suggesting that there is no net effect of the hadronic phase in p-Pb collisions on the Λ(1520) yield.
Inhomogeneous phases in the Gross-Neveu model in 1 + 1 dimensions at finite number of flavors
(2020)
We explore the thermodynamics of the 1+1-dimensional Gross-Neveu (GN) model at a finite number of fermion flavors Nf, finite temperature, and finite chemical potential using lattice field theory. In the limit Nf→∞ the model has been solved analytically in the continuum. In this limit three phases exist: a massive phase, in which a homogeneous chiral condensate breaks chiral symmetry spontaneously; a massless symmetric phase with vanishing condensate; and most interestingly an inhomogeneous phase with a condensate, which oscillates in the spatial direction. In the present work we use chiral lattice fermions (naive fermions and SLAC fermions) to simulate the GN model with 2, 8, and 16 flavors. The results obtained with both discretizations are in agreement. Similarly as for Nf→∞ we find three distinct regimes in the phase diagram, characterized by a qualitatively different behavior of the two-point function of the condensate field. For Nf=8 we map out the phase diagram in detail and obtain an inhomogeneous region smaller as in the limit Nf→∞, where quantum fluctuations are suppressed. We also comment on the existence or absence of Goldstone bosons related to the breaking of translation invariance in 1+1 dimensions.
Type-II multiferroic materials, in which ferroelectric polarization is induced by inversion non-symmetric magnetic order, promise new and highly efficient multifunctional applications based on mutual control of magnetic and electric properties. However, to date this phenomenon is limited to low temperatures. Here we report giant pressure-dependence of the multiferroic critical temperature in CuBr2: at 4.5 GPa it is enhanced from 73.5 to 162 K, to our knowledge the highest TC ever reported for non-oxide type-II multiferroics. This growth shows no sign of saturating and the dielectric loss remains small under these high pressures. We establish the structure under pressure and demonstrate a 60\% increase in the two-magnon Raman energy scale up to 3.6 GPa. First-principles structural and magnetic energy calculations provide a quantitative explanation in terms of dramatically pressure-enhanced interactions between CuBr2 chains. These large, pressure-tuned magnetic interactions motivate structural control in cuprous halides as a route to applied high-temperature multiferroicity.
Deconfinement of Mott localized electrons into topological and spin–orbit-coupled Dirac fermions
(2020)
The interplay of electronic correlations, spin–orbit coupling and topology holds promise for the realization of exotic states of quantum matter. Models of strongly interacting electrons on honeycomb lattices have revealed rich phase diagrams featuring unconventional quantum states including chiral superconductivity and correlated quantum spin Hall insulators intertwining with complex magnetic order. Material realizations of these electronic states are, however, scarce or inexistent. In this work, we propose and show that stacking 1T-TaSe2 into bilayers can deconfine electrons from a deep Mott insulating state in the monolayer to a system of correlated Dirac fermions subject to sizable spin–orbit coupling in the bilayer. 1T-TaSe2 develops a Star-of-David charge density wave pattern in each layer. When the Star-of-David centers belonging to two adyacent layers are stacked in a honeycomb pattern, the system realizes a generalized Kane–Mele–Hubbard model in a regime where Dirac semimetallic states are subject to significant Mott–Hubbard interactions and spin–orbit coupling. At charge neutrality, the system is close to a quantum phase transition between a quantum spin Hall and an antiferromagnetic insulator. We identify a perpendicular electric field and the twisting angle as two knobs to control topology and spin–orbit coupling in the system. Their combination can drive it across hitherto unexplored grounds of correlated electron physics, including a quantum tricritical point and an exotic first-order topological phase transition.
The study of (anti-)deuteron production in pp collisions has proven to be a powerful tool to investigate the formation mechanism of loosely bound states in high energy hadronic collisions. In this paper the production of (anti-)deuterons is studied as a function of the charged particle multiplicity in inelastic pp collisions at s√=13 TeV using the ALICE experiment. Thanks to the large accumulated integrated luminosity, it has been possible to measure (anti-)deuteron production in pp collisions up to the same charged particle multiplicity (dNch/dη∼26) as measured in p-Pb collisions at similar centre-of-mass energies. Within the uncertainties, the deuteron yield in pp collisions resembles the one in p-Pb interactions, suggesting a common formation mechanism behind the production of light nuclei in hadronic interactions. In this context the measurements are compared with the expectations of coalescence and Statistical Hadronisation Models (SHM).
Radiative transition of an excited baryon to a nucleon with emission of a virtual massive photon converting to dielectron pair (Dalitz decays) provides important information about baryon-photon coupling at low q2 in timelike region. A prominent enhancement in the respective electromagnetic transition Form Factors (etFF) at q2 near vector mesons ρ/ω poles has been predicted by various calculations reflecting strong baryon-vector meson couplings. The understanding of these couplings is also of primary importance for the interpretation of the emissivity of QCD matter studied in heavy ion collisions via dilepton emission. Dedicated measurements of baryon Dalitz decays in proton-proton and pion-proton scattering with HADES detector at GSI/FAIR are presented and discussed. The relevance of these studies for the interpretation of results obtained from heavy ion reactions is elucidated on the example of the HADES results.
We estimate the feeddown contributions from decays of unstable A=4 and A=5 nuclei to the final yields of protons, deuterons, tritons, 3He, and 4He produced in relativistic heavy-ion collisions at sNN>2.4 GeV, using the statistical model. The feeddown contribution effects do not exceed 5% at LHC and top RHIC energies due to the large penalty factors involved, but are substantial at intermediate collision energies. We observe large feeddown contributions for tritons, 3He, and 4He at sNN≲10 GeV, where they may account for as much as 70% of the final yield at the lower end of the collision energies considered. Sizable (>10%) effects for deuteron yields are observed at sNN≲4 GeV. The results suggest that the excited nuclei feeddown cannot be neglected in the ongoing and future analysis of light nuclei production at intermediate collision energies, including HADES and CBM experiments at FAIR, NICA at JINR, RHIC beam energy scan and fixed-target programmes, and NA61/SHINE at CERN. We further show that the freeze-out curve in the T-μB plane itself is affected significantly by the light nuclei at high baryochemical potential.
The production of light (anti-)(hyper-)nuclei in heavy-ion collisions at the LHC is considered in the framework of the Saha equation, making use of the analogy between the evolution of the early universe after the Big Bang and that of “Little Bangs” created in the lab. Assuming that disintegration and regeneration reactions involving light nuclei proceed in relative chemical equilibrium after the chemical freeze-out of hadrons, their abundances are determined through the famous cosmological Saha equation of primordial nucleosynthesis and show no exponential dependence on the temperature typical for the thermal model. A quantitative analysis, performed using the hadron resonance gas model in partial chemical equilibrium, shows agreement with experimental data of the ALICE collaboration on d, 3He, HΛ3, and 4He yields for a very broad range of temperatures at T≲155 MeV. The presented picture is supported by the observed suppression of resonance yields in central Pb–Pb collisions at the LHC. Keywords: Light (anti-)(hyper-)nuclei production, Saha equation, Partial chemical equilibrium.
We investigate hadronic particle spectra and flow characteristics of heavy-ion reactions in the FAIR/NICA energy range of 1 AGeV ≤ Elab ≤ 10 AGeV within a relativistic ideal hydrodynamic one-fluid approach. The particlization is realized by sampling the Cooper-Frye distribution for a grand canonical hadron gas on a hypersurface of constant energy density. Results of the hydrodynamic calculations for different underlying equations of state are presented and compared with experimental data and microscopic transport simulations. The sensitivity of the approach to physical model inputs concerning the initial state and the particlization is studied.
We introduce a novel approach based on elas- tic and inelastic scattering rates to extract the hyper-surface of the chemical freeze-out from a hadronic transport model in the energy range from Elab = 1.23 AGeV to √sNN = 62.4 GeV. For this study, the Ultra-relativistic Quantum Molecular Dynamics (UrQMD) model combined with a coarse-graining method is employed. The chemical freeze- out distribution is reconstructed from the pions through sev- eral decay and re-formation chains involving resonances and taking into account inelastic, pseudo-elastic and string excita- tion reactions. The extracted average temperature and baryon chemical potential are then compared to statistical model analysis. Finally we investigate various freeze-out criteria suggested in the literature. We confirm within this micro- scopic dynamical simulation, that the chemical freeze-out at all energies coincides with ⟨E⟩/⟨N⟩ ≈ 1 GeV, while other criteria, like s/T 3 = 7 and nB +nB ̄ ≈ 0.12 fm−3 are limited to higher collision energies.
The production of light (anti-)nuclei and (anti-)hypernuclei in ultra-relativistic heavy-ion collisions, but also in more elementary collisions as proton–proton and proton–nucleus collisions, became recently a focus of interest. In particular, the fact that these objects are all loosely bound compared to the temperature and energies, e.g. the kinetic energies involved, is often stressed out to be special for their production. The binding energies of these (anti-)nuclei is between 130 keV (Λ separation energy in the hypertriton) and about 8 MeV per nucleon. Whereas the connected temperatures are of the order of 100 to 160 MeV. This lead to some difficulties in the interpretation of the usually discussed production models, i.e. coalescence and statistical-thermal models, as will be discussed here. In this brief review we discuss selected highlights of the production of light (anti-)nuclei, such as (anti-)deuteron, (anti-)helium and (anti-)alpha nuclei. In addition, we will discuss the current status of the highly debated lifetime of the (anti-)hypertriton and connected measurements and model results.
Disordered proteins and nucleic acids can condense into droplets that resemble the membraneless organelles observed in living cells. MD simulations offer a unique tool to characterize the molecular interactions governing the formation of these biomolecular condensates, their physicochemical properties, and the factors controlling their composition and size. However, biopolymer condensation depends sensitively on the balance between different energetic and entropic contributions. Here, we develop a general strategy to fine-tune the potential energy function for molecular dynamics simulations of biopolymer phase separation. We rebalance protein–protein interactions against solvation and entropic contributions to match the excess free energy of transferring proteins between dilute solution and condensate. We illustrate this formalism by simulating liquid droplet formation of the FUS low-complexity domain (LCD) with a rebalanced MARTINI model. By scaling the strength of the nonbonded interactions in the coarse-grained MARTINI potential energy function, we map out a phase diagram in the plane of protein concentration and interaction strength. Above a critical scaling factor of αc ≈ 0.6, FUS-LCD condensation is observed, where α = 1 and 0 correspond to full and repulsive interactions in the MARTINI model. For a scaling factor α = 0.65, we recover experimental densities of the dilute and dense phases, and thus the excess protein transfer free energy into the droplet and the saturation concentration where FUS-LCD condenses. In the region of phase separation, we simulate FUS-LCD droplets of four different sizes in stable equilibrium with the dilute phase and slabs of condensed FUS-LCD for tens of microseconds, and over one millisecond in aggregate. We determine surface tensions in the range of 0.01–0.4 mN/m from the fluctuations of the droplet shape and from the capillary-wave-like broadening of the interface between the two phases. From the dynamics of the protein end-to-end distance, we estimate shear viscosities from 0.001 to 0.02 Pa s for the FUS-LCD droplets with scaling factors α in the range of 0.625–0.75, where we observe liquid droplets. Significant hydration of the interior of the droplets keeps the proteins mobile and the droplets fluid.
Disordered proteins and nucleic acids can condense into droplets that resemble the membraneless organelles observed in living cells. MD simulations offer a unique tool to characterize the molecular interactions governing the formation of these biomolecular condensates, their physico-chemical properties, and the factors controlling their composition and size. However, biopolymer condensation depends sensitively on the balance between different energetic and entropic contributions. Here, we develop a general strategy to fine-tune the potential energy function for molecular dynamics simulations of biopolymer phase separation. We rebalance protein-protein interactions against solvation and entropic contributions to match the excess free energy of transferring proteins between dilute solution and condensate. We illustrate this formalism by simulating liquid droplet formation of the FUS low complexity domain (LCD) with a rebalanced MARTINI model. By scaling the strength of the nonbonded interactions in the coarse-grained MARTINI potential energy function, we map out a phase diagram in the plane of protein concentration and interaction strength. Above a critical scaling factor of αc ≈ 0.6, FUS LCD condensation is observed, where α = 1 and 0 correspond to full and repulsive interactions in the MARTINI model, respectively. For a scaling factor α = 0.65, we recover the experimental densities of the dilute and dense phases, and thus the excess protein transfer free energy into the droplet and the saturation concentration where FUS LCD condenses. In the region of phase separation, we simulate FUS LCD droplets of four different sizes in stable equilibrium with the dilute phase and slabs of condensed FUS LCD for tens of microseconds, and over one millisecond in aggregate. We determine surface tensions in the range of 0.01 to 0.4mN/m from the fluctuations of the droplet shape and from the capillary-wave-like broadening of the interface between the two phases. From the dynamics of the protein end-to-end distance, we estimate shear viscosities from 0.001 to 0.02Pas for the FUS LCD droplets with scaling factors α in the range of 0.625 to 0.75, where we observe liquid droplets. Significant hydration of the interior of the droplets keeps the proteins mobile and the droplets fluid.
The spike (S) protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is required for cell entry and is the major focus for vaccine development. We combine cryo electron tomography, subtomogram averaging and molecular dynamics simulations to structurally analyze S in situ. Compared to recombinant S, the viral S is more heavily glycosylated and occurs predominantly in a closed pre-fusion conformation. We show that the stalk domain of S contains three hinges that give the globular domain unexpected orientational freedom. We propose that the hinges allow S to scan the host cell surface, shielded from antibodies by an extensive glycan coat. The structure of native S contributes to our understanding of SARS-CoV-2 infection and the development of safe vaccines. The large scale tomography data set of SARS-CoV-2 used for this study is therefore sufficient to resolve structural features to below 5 Ångstrom, and is publicly available at EMPIAR-10453.
The protein Atg2 has been proposed to form a membrane tether that mediates lipid transfer from the ER to the phagophore in autophagy. However, recent kinetic measurements on the human homolog ATG2A indicated a transport rate of only about one lipid per minute, which would be far too slow to deliver the millions of lipids required to form a phagophore on a physiological time scale. Here, we revisit the analysis of the fluorescence quenching experiments. We develop a detailed kinetic model of the lipid transfer between two membranes bridged by a tether that forms a conduit for lipids. The model provides an excellent fit to the fluorescence experiments, with a lipid transfer rate of about 100 per second and protein. At this rate, Atg2-mediated transfer can supply a significant fraction of the lipids required in autophagosome biogenesis. Our kinetic model is generally applicable to lipid-transfer experiments, in particular to proteins forming organelle contact sites in cells.
The severity of the COVID-19 pandemic, caused by the SARS-CoV-2 coronavirus, calls for the urgent development of a vaccine. The primary immunological target is the SARS-CoV-2 spike (S) protein. S is exposed on the viral surface to mediate viral entry into the host cell. To identify possible antibody binding sites not shielded by glycans, we performed multi-microsecond molecular dynamics simulations of a 4.1 million atom system containing a patch of viral membrane with four full-length, fully glycosylated and palmitoylated S proteins. By mapping steric accessibility, structural rigidity, sequence conservation and generic antibody binding signatures, we recover known epitopes on S and reveal promising epitope candidates for vaccine development. We find that the extensive and inherently flexible glycan coat shields a surface area larger than expected from static structures, highlighting the importance of structural dynamics in epitope mapping.
The neutron capture cross section of 154Gd was measured from 1 eV to 300 keV in the experimental area located 185 m from the CERN n_TOF neutron spallation source, using a metallic sample of gadolinium, enriched to 67% in 154Gd. The capture measurement, performed with four C6D6 scintillation detectors, has been complemented by a transmission measurement performed at the GELINA time-of-flight facility (JRC-Geel), thus minimising the uncertainty related to sample composition. An accurate Maxwellian averaged capture cross section (MACS) was deduced over the temperature range of interest for s process nucleosynthesis modelling. We report a value of 880(50) mb for the MACS at kT = 30 keV, significantly lower compared to values available in literature. The new adopted 154Gd(n,γ) cross section reduces the discrepancy between observed and calculated solar s-only isotopic abundances predicted by s-process nucleosynthesis models.
Higher harmonic non-linear flow modes of charged hadrons in Pb-Pb collisions at √sNN = 5.02 TeV
(2020)
Anisotropic flow coefficients, vn, non-linear flow mode coefficients, χn,mk, and correlations among different symmetry planes, ρn,mk are measured in Pb-Pb collisions at sNN−−−√ = 5.02 TeV. Results obtained with multi-particle correlations are reported for the transverse momentum interval 0.2 < pT < 5.0 GeV/c within the pseudorapidity interval 0.4 < |η| < 0.8 as a function of collision centrality. The vn coefficients and χn,mk and ρn,mk are presented up to the ninth and seventh harmonic order, respectively. Calculations suggest that the correlations measured in different symmetry planes and the non-linear flow mode coefficients are dependent on the shear and bulk viscosity to entropy ratios of the medium created in heavy-ion collisions. The comparison between these measurements and those at lower energies and calculations from hydrodynamic models places strong constraints on the initial conditions and transport properties of the system.
The SU(3) spin model with chemical potential corresponds to a simplified version of QCD with static quarks in the strong coupling regime. It has been studied previously as a testing ground for new methods aiming to overcome the sign problem of lattice QCD. In this work we show that the equation of state and the phase structure of the model can be fully determined to reasonable accuracy by a linked cluster expansion. In particular, we compute the free energy to 14-th order in the nearest neighbour coupling. The resulting predictions for the equation of state and the location of the critical end points agree with numerical determinations to O(1%) and O(10%), respectively. While the accuracy for the critical couplings is still limited at the current series depth, the approach is equally applicable at zero and non-zero imaginary or real chemical potential, as well as to effective QCD Hamiltonians obtained by strong coupling and hopping expansions.
The cumulant ratios up to fourth order of the Z distributions of the largest fragment in spectator fragmentation following 107,124Sn+Sn and 124La+Sn collisions at 600 MeV/nucleon have been investigated. They are found to exhibit the signatures of a second-order phase transition established with cubic bond percolation and previously observed in the ALADIN experimental data for fragmentation of 197Au projectiles at similar energies. The deduced pseudocritical points are found to be only weakly dependent on the A/Z ratio of the fragmenting spectator source. The same holds for the corresponding chemical freeze-out temperatures of close to 6 MeV.The experimental cumulant distributions are quantitatively reproduced with the Statistical Multifragmentation Model and parameters used to describe the experimental fragment multiplicities, isotope distributions and their correlations with impact-parameter related observables in these reactions. The characteristic coincidence of the zero transition of the skewness with the minimum of the kurtosis excess appears to be a generic property of statistical models and is found to coincide with the maximum of the heat capacity in the canonical thermodynamic fragmentation model.
In this thesis different descriptions for the non-Abelian Landau-Pomeranchuk-Migdal (LPM) effect are studied within the partonic transport approach BAMPS (Boltzmann Approach to Multi-Parton Scatterings), which numerically solves the 3+1-dimensional Boltzmann equation for massless partons based on elastic and radiative interactions calculated in perturbative quantum chromodynamics.
The LPM effect is a coherence effect originating from the finite formation time of gluon emissions leading to characteristic dependencies of the radiative energy loss of energetic partonic projectiles, as e.g. jets in ultra-relativistic heavy-ion collisions.
Due to this non-locality of interactions, such coherence effects are difficult to describe rigorously in transport theory.
Therefore we compare in this work three different implementations for the LPM effect: i) a parametric LPM suppression based on a theta function in the radiative matrix elements, ii) a stochastic LPM approach, which explicitly simulates the elastic interactions of gluons during their formation time, and iii) the thermal gluon emission rate from the AMY formalism, which is a hard-thermal-loop calculation exactly considering the non-Abelian LPM effect by resumming ladder diagrams in the large medium limit.
After discussing the numerical implementation of the three approaches, we investigate their consequences in different jet-energy loss scenarios: first the academic scenarios of eikonal and non-eikonal jets flying through a static brick of thermal quark-gluon plasma and then jets traversing the expanding medium of ultra-relativistic heavy-ion collisions at LHC energies.
We can demonstrate that although the different LPM approaches show similarities in the radiative energy loss there are differences in the underlying gluon emission spectra, which originate from the specific treatment of divergences in the matrix elements within BAMPS.
Furthermore, based on the different LPM approaches we present simulation results for recent jet quenching observables from the LHC experiments and discuss properties of the underlying heavy-ion medium.
At the earliest times after a heavy-ion collision, the magnetic field created by the spectator nucleons will generate an extremely strong, albeit rapidly decreasing in time, magnetic field. The impact of this magnetic field may have detectable consequences, and is believed to drive anomalous transport effects like the Chiral Magnetic Effect (CME). We detail an exploratory study on the effects of a dynamical magnetic field on the hydrodynamic medium created in the collisions of two ultrarelativistic heavy-ions, using the framework of numerical ideal MagnetoHydroDynamics (MHD) with the ECHO-QGP code. In this study, we consider a magnetic field captured in a conducting medium, where the conductivity can receive contributions from the electromagnetic conductivity σ and the chiral magnetic conductivity σχ. We first study the elliptic flow of pions, which we show is relatively unchanged by the introduction of a magnetic field. However, by increasing the magnitude of the magnetic field, we find evidence for an enhancement of the elliptic flow in peripheral collisions. This effect is stronger at RHIC than the LHC, and it is evident already at intermediate collision centralities. Next, we explore the impact of the chiral magnetic conductivity on electric charges produced at the edges of the fireball. This initial σχ can be understood as a long-wavelength effective description of chiral fermion production. We then demonstrate that this chiral charge, when transported by the MHD medium, produces a charge dipole perpendicular to the reaction plane which extends a few units in rapidity. Assuming charge conservation at the freeze-out surface, we show that the produced charge imbalance can have measurable effects on some experimental observables, like v1 or ⟨sinϕ⟩. This demonstrates the ability of a MHD fluid to transport the signature of the initial chiral magnetic fields to late times. We also comment on the limitations of the ideal MHD approximation and detail how further development of a dissipative-resistive model can provide a more realistic description of the QGP.
We study odd parity J=1/2 and J=3/2 Ξc resonances using a unitarized coupled-channel framework based on a SU(6)lsf×HQSS-extended Weinberg–Tomozawa baryon–meson interaction, while paying a special attention to the renormalization procedure. We predict a large molecular ΛcK¯ component for the Ξc(2790) with a dominant 0− light-degree-of-freedom spin configuration. We discuss the differences between the 3/2− Λc(2625) and Ξc(2815) states, and conclude that they cannot be SU(3) siblings, whereas we predict the existence of other Ξc-states, one of them related to the two-pole structure of the Λc(2595). It is of particular interest a pair of J=1/2 and J=3/2 poles, which form a HQSS doublet and that we tentatively assign to the Ξc(2930) and Ξc(2970), respectively. Within this picture, the Ξc(2930) would be part of a SU(3) sextet, containing either the Ωc(3090) or the Ωc(3119), and that would be completed by the Σc(2800). Moreover, we identify a J=1/2 sextet with the Ξb(6227) state and the recently discovered Σb(6097). Assuming the equal spacing rule and to complete this multiplet, we predict the existence of a J=1/2 Ωb odd parity state, with a mass of 6360 MeV and that should be seen in the ΞbK¯ channel.
We explore some implications of our previous proposal, motivated in part by the Generalised Uncertainty Principle (GUP) and the possibility that black holes have quantum mechanical hair that the ADM mass of a system has the form M+βM2Pl/(2M), where M is the bare mass, MPl is the Planck mass and β is a positive constant. This also suggests some connection between black holes and elementary particles and supports the suggestion that gravity is self-complete. We extend our model to charged and rotating black holes, since this is clearly relevant to elementary particles. The standard Reissner–Nordström and Kerr solutions include zero-temperature states, representing the smallest possible black holes, and already exhibit features of the GUP-modified Schwarzschild solution. However, interesting new features arise if the charged and rotating solutions are themselves GUP-modified. In particular, there is an interesting transition below some value of β from the GUP solutions (spanning both super-Planckian and sub-Planckian regimes) to separated super-Planckian and sub-Planckian solutions. Equivalently, for a given value of β, there is a critical value of the charge and spin above which the solutions bifurcate into sub-Planckian and super-Planckian phases, separated by a mass gap in which no black holes can form.
We explore the tilted-pulse-front excitation technique to control the superradiant emission of terahertz (THz) pulses from large-area photonconductive semiconductor switches. Two cases are studied. First, a photoconductive antenna emitting into free space, where the propagation direction of the optically generated THz beam is controlled by the choice of the tilt angle of the pump pulse front. Second, a THz waveguide structure with an integrated photoconductive window for the generation of THz radiation, where the injection of the THz radiation into a waveguide mode is optimized by the pulse front tilt. By providing long interaction lengths, such a waveguide-based optical-pump/THz-probe set-up may provide a new platform for the study of diverse short-lived optically induced excitations.
In power systems, flow allocation (FA) methods enable to allocate the usage and costs of the transmission grid to each single market participant. Based on predefined assumptions, the power flow is split into isolated generator-specific or producer-specific sub-flows. Two prominent FA methods, Marginal Participation (MP) and Equivalent Bilateral Exchanges (EBEs), build upon the linearized power flow and thus on the Power Transfer Distribution Factors (PTDFs). Despite their intuitive and computationally efficient concepts, they are restricted to networks with passive transmission elements only. As soon as a significant number of controllable transmission elements, such as high-voltage direct current (HVDC) lines, operate in the system, they lose their applicability. This work reformulates the two methods in terms of Virtual Injection Patterns (VIPs), which allows one to efficiently introduce a shift parameter q to tune contributions of net sources and net sinks in the network. In this work, major properties and differences in the methods are pointed out, and it is shown how the MP and EBE algorithms can be applied to generic meshed AC-DC electricity grids: by introducing a pseudo-impedance ω¯ , which reflects the operational state of controllable elements and allows one to extend the PTDF matrix under the assumption of knowing the current flow in the system. Basic properties from graph theory are used to solve for the pseudo-impedance in dependence of the position within the network. This directly enables, e.g., HVDC lines to be considered in the MP and EBE algorithms. The extended methods are applied to a low-carbon European network model (PyPSA-EUR) with a spatial resolution of 181 nodes and an 18% transmission expansion compared to today’s total transmission capacity volume. The allocations of MP and EBE show that countries with high wind potentials profit most from the transmission grid expansion. Based on the average usage of transmission system expansion, a method of distributing operational and capital expenditures is proposed. In addition, it is shown how injections from renewable resources strongly drive country-to-country allocations and thus cross-border electricity flows.
This thesis discusses important questions of the beam dynamics in the proton-lead operation in the Large Hadron Collider (LHC) at CERN in Geneva. In two time blocks of several weeks in the years 2013 and 2016, proton-lead collisions have so far been successfully generated in the LHC and used by the experiments at the LHC. One reason for doubts regarding the successful operation in proton-lead configuration was the fact that the beams have to be accelerated with different revolution frequencies. There is long-range repulsion between the beams, since both beams share the beam chamber around the interaction points. Because of the different revolution frequencies, the positions of the interaction between the beams shift each revolution. This can lead to resonant excitation and to an increase in the transverse beam emittance, as was observed in the Relativistic Heavy-Ion Collider (RHIC). In this thesis, simulations for the LHC, RHIC and the High-Luminosity Large Hadron Collider (HL-LHC) are performed with a new model. The results for RHIC show relative growth rates of the emittances of the gold beam in gold-deuteron operation in RHIC from 0.1 %/s to 1.5 %/s. Growth rates of this magnitude were observed experimentally in RHIC. Simulations for the LHC show no significant increase of the emittance of the lead beam for different intensities of the counter-rotating beam. The simulation results confirm the measured stability of the beams in the LHC and the issue of strongly increasing emittances in RHIC is reproduced. Also, no significant increase of the emittance is predicted for the Future Circular Collider (FCC) and the HL-LHC.
Using a frequency-map analysis, this work verifies whether the interaction of the lead beam with the much smaller proton beam in the proton-lead operation of the LHC leads to diffusion within the lead beam. Experiences at HERA at DESY in Hamburg and at SppS at CERN have shown that the lifetime of the larger beam can rapidly decrease under certain circumstances. The results of the simulation show no chaotic dynamics near the beam centre of the lead beam. This result is supported by experimental observation.
A program code has been developed which calculates the beam evolution in the LHC by means of coupled differential equations. This study shows that the growth rates of the lead beam due to intra-beam scattering is overestimated and that particle bunches of the lead beam lose more intensity than assumed in the model. The analysis also shows that bunches colliding in a detector suffer additional losses that increase with decreasing crossing angle at the interaction point.
In this work, 2016 data from beam-loss monitors in combination with the luminosity and the loss rate of the beam intensity are used to determine the cross section of proton-lead collisions at the center-of-mass energy of 8.16 TeV. Beam-loss monitors that mainly detect beam losses that are not caused by the collision process itself are used to determine the total cross section via regression. An analysis of the data recorded in 2016 at the center-of-mass energy of 8.16 TeV resulted in a total cross section of σ=(2.32±0.01(stat.)±0.20(sys.)) b. This corresponds approximately to a hadronic cross section of σ(had)=(2.24±0.01(stat.)±0.21(sys.)) b. This value deviates only by 5.7 % from the theoretical value σ(had)=(2.12±0.01) b.
The simulation code for determining the beam evolution is also used to estimate the integrated luminosity of a future one-month run with proton-lead collisions. The result of the study shows that in the future the luminosity in the ATLAS and CMS experiments will increase from 15/nb per day in 2016 to 30/nb per day, which is a significant increase in terms of the performance. This operation, however, requires the use of the TCL collimators to protect the dispersion suppressors at ATLAS and CMS from collision fragments.
This work also gives an outlook on the expected luminosity production in proton-nucleus operation using ion species lighter than lead ions. For example, a change from proton-lead to proton-argon collisions would increase the integrated luminosity from monthly 0.8/nb to 9.4/nb in ATLAS and CMS. This is an increase of one order of magnitude and approximately a doubling of the integrated nucleon-nucleon luminosity. There may be a test operation with proton-oxygen collisions in 2023, which will last only a few days and will be operated with a low luminosity. The LHCf experiment (LHCb experiment) would achieve the desired integrated luminosity of 1.5/nb (2/nb) within 70h (35h) beam time.
In heavy-ion collisions, the quark-gluon plasma is produced far from equilibrium. This regime is currently inaccessible by direct quantum chromodynamics (QCD) computations. In a holographic context, we propose a general method to characterize transport properties based on well-defined two-point functions. We calculate shear transport and entropy far from equilibrium, defining a time-dependent ratio of shear viscosity to entropy density, . Large deviations from its near-equilibrium value , up to a factor of 2.5, are found for realistic situations at the Large Hadron Collider. We predict the far-from-equilibrium time-dependence of to substantially affect the evolution of the QCD plasma and to impact the extraction of QCD properties from flow coefficients in heavy-ion collision data.
i-TED is an innovative detection system which exploits Compton imaging techniques to achieve a superior signal-to-background ratio in (n,γ) cross-section measurements using time-of-flight technique. This work presents the first experimental validation of the i-TED apparatus for high-resolution time-of-flight experiments and demonstrates for the first time the concept proposed for background rejection. To this aim both 197Au(n,γ) and 56Fe(n,γ) reactions were measured at CERN n\_TOF using an i-TED demonstrator based on only three position-sensitive detectors. Two \cds detectors were also used to benchmark the performance of i-TED. The i-TED prototype built for this study shows a factor of ∼3 higher detection sensitivity than state-of-the-art \cds detectors in the ∼10~keV neutron energy range of astrophysical interest. This paper explores also the perspectives of further enhancement in performance attainable with the final i-TED array consisting of twenty position-sensitive detectors and new analysis methodologies based on Machine-Learning techniques.
Evolution of nematic fluctuations in CaK(Fe1−xNix)4As4 with spin-vortex crystal magnetic order
(2020)
The CaK(Fe1−xNix)4As4 superconductors resemble the archetypal 122-type iron-based materials but have a crystal structure with distinctly lower symmetry. This family hosts one of the few examples of the so-called spin-vortex crystal magnetic order, a non-collinear magnetic configuration that preserves tetragonal symmetry, in contrast to the orthorhombic collinear stripe-type magnetic configuration common to the 122-type systems. Thus, nematic order is completely absent from its phase diagram. To investigate the evolution of nematic fluctuations in such a case, we present elastoresistance and elastic modulus measurements in CaK(Fe1−xNix)4As4 (x=0−0.05) combined with phenomenological modeling and density functional theory. We find clear experimental signatures of considerable nematic fluctuations, including softening of the Young's modulus Y[110] and a Curie-Weiss type divergence of the B2g elastoresistance coefficient in CaK(Fe0.951Ni0.049)4As4. Overall, nematic fluctuations within this series bear strong similarities to the hole-doped Ba1−xKxFe2As2 series, including a substitution-induced sign change. Our theoretical analysis addresses the effect of the specific crystal symmetry of the 1144-type structure in determining its magnetic ground state and on the nematic fluctuations.
Binding of the spike protein of SARS-CoV-2 to the human angiotensin converting enzyme 2 (ACE2) receptor triggers translocation of the virus into cells. Both the ACE2 receptor and the spike protein are heavily glycosylated, including at sites near their binding interface. We built fully glycosylated models of the ACE2 receptor bound to the receptor binding domain (RBD) of the SARS-CoV-2 spike protein. Using atomistic molecular dynamics (MD) simulations, we found that the glycosylation of the human ACE2 receptor contributes substantially to the binding of the virus. Interestingly, the glycans at two glycosylation sites, N90 and N322, have opposite effects on spike protein binding. The glycan at the N90 site partly covers the binding interface of the spike RBD. Therefore, this glycan can interfere with the binding of the spike protein and protect against docking of the virus to the cell. By contrast, the glycan at the N322 site interacts tightly with the RBD of the ACE2-bound spike protein and strengthens the complex. Remarkably, the N322 glycan binds into a conserved region of the spike protein identified previously as a cryptic epitope for a neutralizing antibody. By mapping the glycan binding sites, our MD simulations aid in the targeted development of neutralizing antibodies and SARS-CoV-2 fusion inhibitors.
he Pauli Exclusion Principle (PEP) is one of the most basic concepts in physics, but also the most difficult to implement in many-fermion systems, which are common in nuclear physics. To investigate the consequences of ignoring the PEP, we discuss several algebraic models in nuclear structure physics, in particular cluster models. Sometimes they tend to ignore the Pauli Exclusion Principle for practical reasons, leading to flawed interpretations. Though at first sight there seems to be an agreement to experiment, often it is due to the limited number of states known experimentally. We discuss several models which include or not the PEP, illustrating through their differences the importance of the PEP. This contribution is also a review of recently published results.
Cells maintain membrane fluidity by regulating lipid saturation, but the molecular mechanisms of this homeoviscous adaptation remain poorly understood. We have reconstituted the core machinery for regulating lipid saturation in baker’s yeast to study its molecular mechanism. By combining molecular dynamics simulations with experiments, we uncover a remarkable sensitivity of the transcriptional regulator Mga2 to the abundance, position, and configuration of double bonds in lipid acyl chains, and provide insights into the molecular rules of membrane adaptation. Our data challenge the prevailing hypothesis that membrane fluidity serves as the measured variable for regulating lipid saturation. Rather, we show that Mga2 senses the molecular lipid-packing density in a defined region of the membrane. Our findings suggest that membrane property sensors have evolved remarkable sensitivities to highly specific aspects of membrane structure and dynamics, thus paving the way toward the development of genetically encoded reporters for such properties in the future.
Twenty years ago, on February 10, 2000, the CERN Director General Luciano Maiani announced: The combined data coming from the seven experiments on CERN’s Heavy Ion programme have given a clear picture of a new state of matter. This result verifies an important prediction of the present theory of fundamental forces between quarks. This report briefly reviews studies of the phase diagram of strongly interacting matter with relativistic nuclear collisions at the CERN Super Proton Synchrotron which followed the CERN’s press release on the quark-gluon plasma discovery. An attempt to formulate priorities for future measurements at the CERN SPS closes the paper. The report is dedicated to David Blaschke who celebrated his 60th birthday in 2019. David’s contribution to the studies presented here was very significant.