Refine
Year of publication
Document Type
- Article (1959)
- Preprint (1346)
- Doctoral Thesis (597)
- Conference Proceeding (249)
- diplomthesis (100)
- Bachelor Thesis (75)
- Master's Thesis (61)
- Contribution to a Periodical (46)
- Diploma Thesis (34)
- Book (33)
Keywords
- Kollisionen schwerer Ionen (47)
- heavy ion collisions (44)
- LHC (25)
- Quark-Gluon-Plasma (25)
- Heavy Ion Experiments (20)
- BESIII (19)
- equation of state (19)
- quark-gluon plasma (19)
- Relativistic heavy-ion collisions (18)
- heavy-ion collisions (16)
Institute
- Physik (4595) (remove)
The thermodynamics of Quantum Chromodynamics (QCD) in external (electro-)magnetic fields shows some unexpected features like inverse magnetic catalysis, which have been revealed mainly through lattice studies. Many effective descriptions, on the other hand, use Landau levels or approximate the system by just the lowest Landau level (LLL). Analyzing lattice configurations we ask whether such a picture is justified. We find the LLL to be separated from the rest by a spectral gap in the two-dimensional Dirac operator and analyze the corresponding LLL signature in four dimensions. We determine to what extent the quark condensate is LLL dominated at strong magnetic fields.
The main phospholipid (MPL) of Thermoplasma acidophilum DSM 1728 was isolated, purified and physico-chemically characterized by differential scanning calorimetry (DSC)/differential thermal analysis (DTA) for its thermotropic behavior, alone and in mixtures with other lipids, cholesterol, hydrophobic peptides and pore-forming ionophores. Model membranes from MPL were investigated; black lipid membrane, Langmuir-Blodgett monolayer, and liposomes. Laboratory results were compared to computer simulation. MPL forms stable and resistant liposomes with highly proton-impermeable membrane and mixes at certain degree with common bilayer-forming lipids. Monomeric bacteriorhodopsin and ATP synthase from Micrococcus luteus were co-reconstituted and light-driven ATP synthesis measured. This review reports about almost four decades of research on Thermoplasma membrane and its MPL as well as transfer of this research to Thermoplasma species recently isolated from Indonesian volcanoes.
Neutron-induced reaction cross sections are important for a wide variety of research fields ranging from the study of nuclear level densities, nucleosynthesis to applications of nuclear technology like design, and criticality and safety assessment of existing and future nuclear reactors, radiation dosimetry, medical applications, nuclear waste transmutation, accelerator-driven systems and fuel cycle investigations. Simulations and calculations of nuclear technology applications largely rely on evaluated nuclear data libraries. The evaluations in these libraries are based both on experimental data and theoretical models. CERN’s neutron time-of-flight facility n_TOF has produced a considerable amount of experimental data since it has become fully operational with the start of its scientific measurement programme in 2001. While for a long period a single measurement station (EAR1) located at 185 m from the neutron production target was available, the construction of a second beam line at 20 m (EAR2) in 2014 has substantially increased the measurement capabilities of the facility. An outline of the experimental nuclear data activities at n_TOF will be presented.
Vertebrate life depends on renal function to filter excess fluid and remove low-molecular-weight waste products. An essential component of the kidney filtration barrier is the slit diaphragm (SD), a specialized cell-cell junction between podocytes. Although the constituents of the SD are largely known, its molecular organization remains elusive. Here, we use super-resolution correlative light and electron microscopy to quantify a linear rate of reduction in albumin concentration across the filtration barrier. Next, we use cryo-electron tomography of vitreous lamellae from high-pressure frozen native glomeruli to analyze the molecular architecture of the SD. The resulting densities resemble a fishnet pattern. Fitting of Nephrin and Neph1, the main constituents of the SD, results in a complex interaction pattern with multiple contact sites between the molecules. Using molecular dynamics flexible fitting, we construct a blueprint of the SD, where we describe all interactions. Our architectural understanding of the SD reconciles previous findings and provides a mechanistic framework for the development of novel therapies to treat kidney dysfunction.
Vertebrate life depends on renal function to filter excess fluid and remove low-molecular-weight waste products. An essential component of the kidney filtration barrier is the slit diaphragm (SD), a specialized cell-cell junction between podocytes. Although the constituents of the SD are largely known, its molecular organization remains elusive. Here, we use super-resolution correlative light and electron microscopy to quantify a linear rate of reduction in albumin concentration across the filtration barrier under no-flow conditions. Next, we use cryo-electron tomography of vitreous lamellae from high-pressure frozen native glomeruli to analyze the molecular architecture of the SD. The resulting densities resemble a fishnet pattern. Fitting of Nephrin and Neph1, the main constituents of the SD, results in a complex interaction pattern with multiple contact sites between the molecules. Using molecular dynamics simulations, we construct a blueprint of the SD that explains its molecular architecture. Our architectural understanding of the SD reconciles previous findings and provides a mechanistic framework for the development of novel therapies to treat kidney dysfunction.
A key event in cellular physiology is the decision between membrane biogenesis and fat storage. Phosphatidic acid (PA) is an important intermediate at the branch point of these pathways and is continuously monitored by the transcriptional repressor Opi1 to orchestrate lipid metabolism. In this study, we report on the mechanism of membrane recognition by Opi1 and identify an amphipathic helix (AH) for selective binding of PA over phosphatidylserine (PS). The insertion of the AH into the membrane core renders Opi1 sensitive to the lipid acyl chain composition and provides a means to adjust membrane biogenesis. By rational design of the AH, we tune the membrane-binding properties of Opi1 and control its responsiveness in vivo. Using extensive molecular dynamics simulations, we identify two PA-selective three-finger grips that tightly bind the PA phosphate headgroup while interacting less intimately with PS. This work establishes lipid headgroup selectivity as a new feature in the family of AH-containing membrane property sensors.
A key event in cellular physiology is the decision between membrane biogenesis and fat storage. Phosphatidic acid (PA) is an important lipid intermediate and signaling lipid at the branch point of these pathways and constantly monitored by the transcriptional repressor Opi1 to orchestrate lipid metabolism. Here, we report on the mechanism of membrane recognition by Opi1 and identify an amphipathic helix (AH) for the selective binding to membranes containing PA over phosphatidylserine (PS). The insertion of the AH into the hydrophobic core of the membrane renders Opi1 sensitive to the lipid acyl chain composition as an important factor contributing to the regulation of membrane biogenesis. Based on these findings, we rationally designed the membrane binding properties of Opi1 to control its responsiveness in the physiological context. Using extensive molecular dynamics (MD) simulations, we identified two PA-selective three-finger grips that tightly bind the phosphate headgroup, while interacting less intimately and more transiently with PS. This work establishes lipid headgroup selectivity as a new feature in the family of AH-containing membrane property sensors.
Accelerator Driven Systems (ADS) are promising tools for the efficient transmutation of nuclear waste products in dedicated industrial installations, called transmuters. The Myrrha project at Mol, Belgium, placed itself on the path towards these applications with a multipurpose and versatile system based on a liquid PbBi (LBE) cooled fast reactor (80 MWth) which may be operated in both critical and subcritical modes. In the latter case the core is fed by spallation neutrons obtained from a 600 MeV proton beam hitting the LBE coolant/target. The accelerator providing this beam is a high intensity CW superconducting linac which is laid out for the highest achievable reliability. The combination of a parallel redundant and of a fault tolerant scheme should allow obtaining an MTBF value in excess of 250 hours that is required for optimal integrity and successful operation of the ADS. Myrrha is expected to be operational in 2023. The forthcoming 4-year period is fully dedicated to R&D activities, and in the field of the accelerator they are strongly focused on the reliability aspects and on the proper shaping of the beam trip spectrum.
The CERN n_TOF neutron beam facility is characterized by a very high instantaneous neutron flux, excellent TOF resolution at the 185 m long flight path (EAR-1), low intrinsic background and coverage of a wide range of neutron energies, from thermal to a few GeV. These characteristics provide a unique possibility to perform high-accuracy measurements of neutron-induced reaction cross-sections and angular distributions of interest for fundamental and applied Nuclear Physics. Since 2001, the n_TOF Collaboration has collected a wealth of high quality nuclear data relevant for nuclear astrophysics, nuclear reactor technology, nuclear medicine, etc. The overall efficiency of the experimental program and the range of possible measurements has been expanded with the construction of a second experimental area (EAR-2), located 20 m on the vertical of the n_TOF spallation target. This upgrade, which benefits from a neutron flux 30 times higher than in EAR-1, provides a substantial extension in measurement capabilities, opening the possibility to collect data on neutron cross-section of isotopes with short half-lives or available in very small amounts. This contribution will outline the main characteristics of the n_TOF facility, with special emphasis on the new experimental area. In particular, we will discuss the innovative features of the EAR-2 neutron beam that make possible to perform very challenging measurements on short-lived radioisotopes or sub-mg samples, out of reach up to now at other neutron facilities around the world. Finally, the future perspectives of the facility will be presented.
The nature of spontaneous brain activity during wakefulness and sleep: a complex systems approach
(2014)
In this thesis we study the organization of spontaneous brain activity during wakefulness and all stages of human non-rapid eye movement sleep using an approach based on developments and tools from the theory of complex systems. After a brief introduction to sleep physiology and different theoretical models of consciousness, we study how the organization of cortical and sub-cortical interactions is modified during the sleep cycle. Our results, obtained by modeling global brain activity as a complex functional interaction network, show that the capacity of the human brain to integrate different segregated functional modules is diminished during deep sleep, in line with an informationintegration account of consciousness. We then show that integration is impaired not only across space but also in the temporal domain, by assesing the emergence of long-range temporal correlations in brain activity and how they are modified during sleep. We propose an encompassing explanation for this observation, namely, that the brain operatsat different dynamical regimes during different states of consciousness. Finally, we gather massive amounts of data from different collaborative projects and apply machine learning techniques to reveal that the \resting state" cannot be considered as a pure brain state and is in fact a mixture containing different levels of conscious awareness. This last result has deep implications for future attempts to develop a discovery science of brain function both in health and disease.
The family of cubic noncentrosymmetric 3-4-3 compounds has become a fertile ground for the discovery of novel correlated metallic and insulating phases. Here, we report the synthesis of a new heavy fermion compound, Ce3Bi4Ni3. It is an isoelectronic analog of the prototypical Kondo insulator Ce3Bi4Pt3 and of the recently discovered Weyl-Kondo semimetal Ce3Bi4Pd3. In contrast to the volume-preserving Pt-Pd substitution, structural and chemical analyses reveal a positive chemical pressure effect in Ce3Bi4Ni3 relative to its heavier counterparts. Based on the results of electrical resistivity, Hall effect, magnetic susceptibility, and specific heat measurements, we identify an energy gap of 65-70 meV, about 8 times larger than that in Ce3Bi4Pt3 and about 45 times larger than that of the Kondo-insulating background hosting the Weyl nodes in Ce3Bi4Pd3. We show that this gap as well as other physical properties do not evolve monotonically with increasing atomic number, i.e., in the sequence Ce3Bi4Ni3-Ce3Bi4Pd3-Ce3Bi4Pt3, but instead with increasing partial electronic density of states of the d orbitals at the Fermi energy. To understand under which condition topological states form in these materials is a topic for future studies.
The KADoNiS (Karlsruhe Astrophysical Database of Nucleosynthesis in Stars) project is an online
database (www.kadonis.org) for cross sections relevant to the s-process and the p-process.
The first version was an updated sequel to the previous Bao et al. [1] compilations from 1987
and 2000 for (n; g) cross sections relevant to Big Bang and s-process nucleosynthesis. The first
update, KADoNiS v0.2, was published in 2006 [2]. It contained mainly Maxwellian averaged
(n; g) cross sections relevant to the s-process, and some experimental charged particle induced
reaction relevant to the p-process. After that a second update was presented in 2009 [3].
Recently, we started to collect and review all existing experimental data relevant for p-process
nucleosynthesis and to provide a user-friendly database based on the KADoNiS framework. The
p-process part of the KADoNiS database is currently being extended and will include all available
experimental data from (p; g), (p;n), (p;a), (a,g), (a;n) and (a; p) reactions in or close to the
respective Gamow window.
We extend the standard solid-state quantum mechanical Hamiltonian containing only Coulomb interactions between the charged particles by inclusion of the (transverse) current-current diamagnetic interaction starting from the non-relativistic QED restricted to the states without photons and neglecting the retardation in the photon propagator. This derivation is supplemented with a derivation of an analogous result along the non-rigorous old classical Darwin-Landau-Lifshitz argumentation within the physical Coulomb gauge.
An important experimental program on Nuclear Astrophysics is being carried out at the n_TOF since several years, in order to address the still open issues in stellar and primordial nucleosynthesis. Several neutron capture reactions relevant to s-process nucleosynthesis have been measured so far, some of which on important branching point radioisotopes. Furthermore, the construction of a second experimental area has recently opened the way to challenging measurements of (n, charged particle) reactions on isotopes of short half-life. The Nuclear Astrophysics program of the n_TOF Collaboration is here described, with emphasis on recent results relevant for stellar nucleosynthesis, stellar neutron sources and primordial nucleosynthesis.
We investigate the role of the Pauli Exclusion Principle (PEP) for light nuclei, at the examples of 12C and 16O. We show that ignoring the PEP does lead not only to a too dense spectrum at low energy but also to a wrong grouping into bands. Using a geometrical mapping, a triangular structure for 12C and a tetrahedral structure in 16O in the ground state is obtained by using the indistinguishably of the α-particles.
We have measured the radiative neutron-capture cross section and the total neutron-induced cross section of one of the most important isotopes for the s process, the 25Mg. The measurements have been carried out at the neutron time-of-flight facilities n_TOF at CERN (Switzerland) and GELINA installed at the EC-JRC-IRMM (Belgium). The cross sections as a function of neutron energy have been measured up to approximately 300 keV, covering the energy region of interest to the s process. The data analysis is ongoing and preliminary results show the potential relevance for the s process.
Chapter 1 contains the general background of our work. We briefly discuss important aspects of quantum chromodynamics (QCD) and introduce the concept of the chiral condensate as an order parameter for the chiral phase transition. Our focus is on the concept of universality and the arguments why the O(4) model should fall into the same universality class as the effective Lagrangian for the order parameter of (massless) two-flavor QCD. Chapter 2 pedagogically explains the CJT formalism and is concerned with the WKB method. In chapter 3 the CJT formalism is then applied to a simple Z(2) symmetric toy model featuring a one-minimum classical potential. As for all other models we are concerned with in this thesis, we study the behavior at nonzero temperature. This is done in 1+3 dimensions as well as in 1+0 dimensions. In the latter case we are able to compare the effective potential at its global minimum (which is minus the pressure) with our result from the WKB approximation. In chapter 4 this program is also carried out for the toy model with a double-well classical potential, which allows for spontaneous symmetry breaking and tunneling. Our major interest however is in the O(2) model with the fields treated as polar coordinates. This model can be regarded as the first step towards the O(4) model in four-dimensional polar coordinates. Although in principle independent, all subjects discussed in this thesis are directly related to questions arising from the investigation of this particular model. In chapter 5 we start from the generating functional in cartesian coordinates and carry out the transition to polar coordinates. Then we are concerned with the question under which circumstances it is allowed to use the same Feynman rules in polar coordinates as in cartesian coordinates. This question turns out to be non-trivial. On the basis of the common Feynman rules we apply the CJT formalism in chapter 6 to the polar O(2) model. The case of 1+0 dimensions was intended to be a toy model on the basis of which one could more easily explore the transition to polar coordinates. However, it turns out that we are faced with an additional complication in this case, the infrared divergence of thermal integrals. This problem requires special attention and motivates the explicit study of a massless field under topological constraints in chapter 8. In chapter 7 we investigate the cartesian O(2) model in 1+0 dimensions. We compare the effective potential at its global minimum calculated in the CJT formalism and via the WKB approximation. Appendix B reviews the derivation of standard thermal integrals in 1+0 and 1+3 dimensions and constitutes the basis for our CJT calculations and the discussion of infrared divergences. In chapter 9 we discuss the so-called path integral collapse and propose a solution of this problem. In chapter 10 we present our conclusions and an outlook. Since we were interested in organizing our work as pedagogical as possible within the narrow scope of a diploma thesis, we decided to make extensive use of appendices. Appendices A-H are intended for students who are not familiar with several important concepts we are concerned with. We will refer to them explicitly to establish the connection between our work and the general context in which it is settled.
Chapter 1 contains the general background of our work. We briefly discuss important aspects of quantum chromodynamics (QCD) and introduce the concept of the chiral condensate as an order parameter for the chiral phase transition. Our focus is on the concept of universality and the arguments why the O(4) model should fall into the same universality class as the effective Lagrangian for the order parameter of (massless) two-flavor QCD. Chapter 2 pedagogically explains the CJT formalism and is concerned with the WKB method. In chapter 3 the CJT formalism is then applied to a simple Z2 symmetric toy model featuring a one-minimum classical potential. As for all other models we are concerned with in this thesis, we study the behavior at nonzero temperature. This is done in 1+3 dimensions as well as in 1+0 dimensions. In the latter case we are able to compare the effective potential at its global minimum (which is minus the pressure) with our result from the WKB approximation. In chapter 4 this program is also carried out for the toy model with a double-well classical potential, which allows for spontaneous symmetry breaking and tunneling. Our major interest however is in the O(2) model with the fields treated as polar coordinates. This model can be regarded as the first step towards the O(4) model in four-dimensional polar coordinates. Although in principle independent, all subjects discussed in this thesis are directly related to questions arising from the investigation of this particular model. In chapter 5 we start from the generating functional in cartesian coordinates and carry out the transition to polar coordinates. Then we are concerned with the question under which circumstances it is allowed to use the same Feynman rules in polar coordinates as in cartesian coordinates. This question turns out to be non-trivial. On the basis of the common Feynman rules we apply the CJT formalism in chapter 6 to the polar O(2) model. The case of 1+0 dimensions was intended to be a toy model on the basis of which one could more easily explore the transition to polar coordinates. However, it turns out that we are faced with an additional complication in this case, the infrared divergence of thermal integrals. This problem requires special attention and motivates the explicit study of a massless field under topological constraints in chapter 8. In chapter 7 we investigate the cartesian O(2) model in 1+0 dimensions. We compare the effective potential at its global minimum calculated in the CJT formalism and via the WKB approximation. Appendix B reviews the derivation of standard thermal integrals in 1+0 and 1+3 dimensions and constitutes the basis for our CJT calculations and the discussion of infrared divergences. In chapter 9 we discuss the so-called path integral collapse and propose a solution of this problem. In chapter 10 we present our conclusions and an outlook. Since we were interested in organizing our work as pedagogical as possible within the narrow scope of a diploma thesis, we decided to make extensive use of appendices. Appendices A-H are intended for students who are not familiar with several important concepts we are concerned with. We will refer to them explicitly to establish the connection between our work and the general context in which it is settled.
Of central importance in the whole thesis is the concept of the generating functional and the partition function, respectively. In appendix A.1 we present the general context in which the partition function appears and its general definition within the operator formalism of second quantization. Alternatively, this definition can be rewritten via the path integral formalism. We restrict ourselves to scalar fields in this case. Furthermore, the understanding of the CJT formalism is based on knowledge about n-point functions (connected or disconnected, in the presence or in the absence of sources) and the context in which they arise. In appendix A.2 we give their definition taking account of the different modifications in which these quantities occur in this thesis, i.e., scalar field theory at zero or at nonzero temperature, respectively. From a didactic point of view, we believe that it is helpful if one can establish a relation between special cases and a general framework. Therefore, in appendix A.3 we want to keep an eye on the overall picture. We discuss the general concept of the generating functional for correlation functions, which also covers the partition function. We also briefly comment on the general concept of Feynman rules and we clarify the meaning of the terms Green’s function and propagator.
The properties of the outer crust of non-accreting cold neutron stars are studied by using modern nuclear data and theoretical mass tables updating in particular the classic work of Baym, Pethick and Sutherland. Experimental data from the atomic mass table from Audi, Wapstra, and Thibault of 2003 is used and a thorough comparison of many modern theoretical nuclear models, relativistic and non-relativistic ones, is performed for the first time. In addition, the influences of pairing and deformation are investigated. State-of-the-art theoretical nuclear mass tables are compared in order to check their differences concerning the neutron dripline, magic neutron numbers, the equation of state, and the sequence of neutron-rich nuclei up to the dripline in the outer crust of non-accreting cold neutron stars.
Hadronic yields and yield ratios observed in Pb+Pb collisions at the SPS energy of 158 GeV per nucleon are known to resemble a thermal equilibrium population at T=180 +/- 10 MeV, also observed in elementary e+ + e- to hadron data at LEP. We argue that this is the universal consequence of the QCD parton to hadron phase transition populating the maximum entropy state. This state is shown to survive the hadronic rescattering and expansion phase, freezing in right after hadronization due to the very rapid longitudinal and transverse expansion that is inferred from Bose-Einstein pion correlation analysis of central Pb+Pb collisions.
A selection of recent data referring to Pb+Pb collisions at the SPS CERN energy of 158 GeV per nucleon is presented which might describe the state of highly excited strongly interacting matter both above and below the deconfinement to hadronization (phase) transition predicted by lattice QCD. A tentative picture emerges in which a partonic state is indeed formed in central Pb+Pb collisions which hadronizes at about T = 185 MeV, and expands its volume more than tenfold, cooling to about 120 MeV before hadronic collisions cease. We suggest further that all SPS collisions, from central S+S onward, reach that partonic phase, the maximum energy density increasing with more massive collision systems.
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, I study the phase diagram of dense, locally neutral three-flavor quark matter as a function of the strange quark mass, the quark chemical potential, and the temperature, employing a general nine-parameter ansatz for the gap matrix. At zero temperature and small values of the strange quark mass, the ground state of quark matter corresponds to the color–flavor-locked (CFL) phase. At some critical value of the strange quark mass, this is replaced by the recently proposed gapless CFL (gCFL) phase. I also find several other phases, for instance, a metallic CFL (mCFL) phase, a so-called uSC phase where all colors of up quarks are paired, as well as the standard two-flavor color-superconducting (2SC) phase and the gapless 2SC (g2SC) phase. I also study the phase diagram of dense, locally neutral three-flavor quark matter within the framework of a Nambu–Jona-Lasinio (NJL) model. In the analysis, dynamically generated quark masses are taken into account self-consistently. The phase diagram in the plane of temperature and quark chemical potential is presented. The results for two qualitatively different regimes, intermediate and strong diquark coupling strength, are presented. It is shown that the role of gapless phases diminishes with increasing diquark coupling strength. In addition, I study the effect of neutrino trapping on the phase diagram of dense, locally neutral three-flavor quark matter within the same NJL model. The phase diagrams in the plane of temperature and quark chemical potential, as well as in the plane of temperature and leptonnumber chemical potential are presented. I show that neutrino trapping favors two-flavor color superconductivity and disfavors the color–flavor-locked phase at intermediate densities of matter. At the same time, the location of the critical line separating the two-flavor color-superconducting phase and the normal phase of quark matter is little affected by the presence of neutrinos. The implications of these results for the evolution of protoneutron stars are briefly discussed.
We study the phase diagram of dense, locally neutral three-flavor quark matter within the framework of the Nambu--Jona-Lasinio model. In the analysis, dynamically generated quark masses are taken into account self-consistently. The phase diagram in the plane of temperature and quark chemical potential is presented. The results for two qualitatively different regimes, intermediate and strong diquark coupling strength, are presented. It is shown that the role of gapless phases diminishes with increasing diquark coupling strength.
We study the effect of neutrino trapping on the phase diagram of dense, locally neutral three-flavor quark matter within the framework of a Nambu--Jona-Lasinio model. In the analysis, dynamically generated quark masses are taken into account self-consistently. The phase diagrams in the plane of temperature and quark chemical potential, as well as in the plane of temperature and lepton-number chemical potential are presented. We show that neutrino trapping favors two-flavor color superconductivity and disfavors the color-flavor-locked phase at intermediate densities of matter. At the same time, the location of the critical line separating the two-flavor color-superconducting phase and the normal phase of quark matter is little affected by the presence of neutrinos. The implications of these results for the evolution of protoneutron stars are briefly discussed. PACS numbers: 12.39.-x 12.38.Aw 26.60.+c
The phase diagram of the square lattice bilayer Hubbard model: a variational Monte Carlo study
(2014)
We investigate the phase diagram of the square lattice bilayer Hubbard model at half-filling with the variational Monte Carlo method for both the magnetic and the paramagnetic case as a function of the interlayer hopping and on-site Coulomb repulsion U. With this study we resolve some discrepancies in previous calculations based on the dynamical mean-field theory, and we are able to determine the nature of the phase transitions between metal, Mott insulator and band insulator. In the magnetic case we find only two phases: an antiferromagnetic Mott insulator at small for any value of U and a band insulator at large . At large U values we approach the Heisenberg limit. The paramagnetic phase diagram shows at small a metal to Mott insulator transition at moderate U values and a Mott to band insulator transition at larger U values. We also observe a re-entrant Mott insulator to metal transition and metal to band insulator transition for increasing in the range of . Finally, we discuss the phase diagrams obtained in relation to findings from previous studies based on different many-body approaches.
We study the decays of the JPC=1−+ hybrid nonet using a Lagrangian invariant under the flavor symmetry, parity reversal, and charge conjugation. We use the available experimental data, the lattice predictions, and the flavor constraints to evaluate the coupling strengths of the π1(1600) to various two-body mesonic states. Using these coupling constants, we estimate the partial widths of the two-body decays of the hybrid pion, kaon and the isoscalars. We find that the hybrid kaon can be nearly as broad as the π1(1600). Quite remarkably, we find also that the light isoscalar must be significantly narrow while the width of the heavy isoscalar can be matched to the recently observed η1(1855).
The physics of EPOS
(2013)
We extend our previous studies [PhysRevD.90.054509, PhysRevD.92.094510] of the pion quasiparticle in the low-temperature phase of two-flavor QCD with support from chiral effective theory. This includes the analysis performed on a finite temperature ensemble of size 20 × 643 at T ≈ 151MeV and a lighter zero-temperature pion mass mπ ≈ 185 MeV. Furthermore, we investigate the Gell-Mann–Oakes-Renner relation at finite temperature and the Dey-Eletsky-Ioffe mixing theorem at finite quark mass.
To reach high luminosities in future linear colliders short range wakes havea to be controlled in the range of X-band frequencies or higher. Rectangular irises can be used to introduce strong focusing quadrupole-like rf-fields. Even circular irises in iris-loaded accelarator structures have the capability of focusing if the particle velocity differs from phase velocity. Theoretical investigations concerning the focusing strength to be expected are presented. Their applicability for linear colliders is discussed.
The properties of compact stars and in particular the existence of twin star solutions are investigated within an effective model that is constrained by lattice QCD thermodynamics. The model is modified at large baryon densities to incorporate a large variety of scenarios of first order phase transitions to a phase of deconfined quarks. This is achieved by matching two different variants of the bag model equation of state, in order to estimate the role of the Bag model parameters on the appearance of a second family of neutron stars. The produced sequences of neutron stars are compared with modern constrains on stellar masses, radii, and tidal deformability from astrophysical observations and gravitational wave analyses. It is found that those scenarios in our analysis, in which a third family of stars appeared due to the deconfinement transition, are disfavored from astrophysical constraints.
The study of meson production in proton-proton collisions in the energy range
up to one GeV above the production threshold provides valuable information about
the nature of the nucleon-nucleon interaction. Theoretical models describe the interaction
between nucleons via the exchange of mesons. In such models, different
mechanisms contribute to the production of the mesons in nucleon-nucleon collisions.
The measurement of total and differential production cross sections provide information
which can help in determining the magnitude of the various mechanisms.
Moreover, such cross section information serves as an input to the transport calculations
which describe e.g. the production of e+e− pairs in proton- and pion-induced
reactions as well as in heavy ion collisions.
In this thesis, the production of ω and η mesons in proton-proton collisions at 3.5
GeV beam energy was studied using the High Acceptance DiElectron Spectrometer
(HADES) installed at the Schwerionensynchrotron (SIS 18) at the Helmholtzzenturm
f¨ur Schwerionenforschung in Darmstadt.
About 80 000 ω mesons and 35 000 η mesons were reconstructed. Total production
cross sections of both mesons were determined. Furthermore, the collected statistics
allowed for extracting angular distributions of both mesons as well as performing
Dalitz plot studies.
The ω and η mesons were reconstructed via their decay into three pions (π+π−π0)
in the exclusive reaction pp −→ ppπ+π−π0. The charged particles were identified
via their characteristic energy loss, via the measurement of their time of flight and
momentum, or using kinematics.
The neutral pion was reconstructed using the missing mass method. A kinematic
fit was applied to improve the resolution and to select events in which a π0 was
produced.
The correction of measured yields for the effects of spectrometer acceptance was done
as a function of four variables (two invariant masses and two angles). Systematic
studies of the acceptance for different input distributions were performed.
The measured yields were normalized to the number of measured events of elastic
scattering. Systematic errors due to the methods of the data analysis and the
background subtraction were investigated.
Production angular distributions of ω and η mesons were measured. Both mesons
exhibit a slightly anisotropic angular distribution.
The Dalitz plot of ω meson production shows indications of resonant production.
However, the deviation of the distribution from the one expected by phase space
simulations is not large.
The Dalitz plot of η meson production shows a signal of the production via the
N(1535) resonance, The contribution of N(1535) to the production was quantified
to be about 47%. The angular distribution of η mesons does not show significant
differences between resonant and non resonant production.
The total production cross section of ω mesons in the reaction pp −→ ppω was
determined to be 106.5 ± 0.9 (stat) ± 7.9 (sys) [μb] where stat indicates statistical
error and sys indicates systematic error, while that of η mesons was determined to
be 136.9 ± 0.9 (stat) ± 10.1 (sys) [μb] in the reaction pp −→ ppη
We present the first measurement of the proton–Ω correlation function in heavy-ion collisions for the central (0–40%) and peripheral (40–80%) Au + Au collisions at √sNN = 200 GeV by the STAR experiment at the Relativistic Heavy-Ion Collider (RHIC). Predictions for the ratio of peripheral collisions to central collisions for the proton–Ω correlation function are sensitive to the presence of a nucleon– bound state. These predictions are based on the proton– interaction extracted from (2 + 1)-flavor lattice QCD calculations at the physical point. The measured ratio of the proton–Ω correlation function between the peripheral (small system) and central (large system) collisions is less than unity for relative momentum smaller than 40 MeV/c. Comparison of our measured correlation ratio with theoretical calculation slightly favors a proton– bound system with a binding energy of ∼ 27 MeV.
We present a numerical technique for calculating path integrals in non-compact U(1) and SU(2) gauge theories. The gauge fields are represented by a superposition of pseudoparticles of various types with their amplitudes and color orientations as degrees of freedom. Applied to Maxwell theory this technique results in a potential which is in excellent agreement with the Coulomb potential. For SU(2) Yang-Mills theory the same technique yields clear evidence of confinement. Varying the coupling constant exhibits the same scaling behavior for the string tension, the topological susceptibility and the critical temperature while their dimensionless ratios are similar to those obtained in lattice calculations.
The advent of improved experimental and theoretical techniques has brought a lot of attention to the electric dipole (E1) response of atomic nuclei in the last decade. The extensive studies have led to the observation and interpretation of a concentration of E1 strength energetically below the Giant Dipole Resonance in many nuclei. This phenomenon is commonly denoted as Pygmy Dipole Resonance (PDR). This contribution will summarize the most important results obtained using different experimental probes, define the challenges to gain a deeper understanding of the excitations, and discuss the newest experimental developments.
We present an extensive experimental study of the recently predicted pygmy quadrupole resonance (PQR) in Sn isotopes, where complementary probes were used. In this study, (α,α' γ ) and (γ , γ') experiments were performed on 124Sn. In both reactions, Jπ = 2+ states below an excitation energy of 5 MeV were populated. The E2 strength integrated over the full transition densities could be extracted from the (γ , γ') experiment, while the (α,α'γ ) experiment at the chosen kinematics strongly favors the excitation of surface modes because of the strong α-particle absorption in the nuclear interior. The excitation of such modes is in accordance with the quadrupole-type oscillation of the neutron skin predicted by a microscopic approach based on self-consistent density functional theory and the quasiparticle-phonon model (QPM). The newly determined γ -decay branching ratios hint at a non-statistical character of the E2 strength, as it has also been recently pointed out for the case of the pygmy dipole resonance (PDR). This allows us to distinguish between PQR-type and multiphonon excitations and, consequently, supports the recent first experimental indications of a PQR in 124Sn.
Quenched QCD at zero baryonic chemical potential undergoes a first-order deconfinement phase transition at a critical temperature Tc, which is related to the spontaneous breaking of the global center symmetry. Including heavy, dynamical quarks breaks the center symmetry explicitly and weakens the first-order phase transition. For decreasing quark masses the first-order phase transition turns into a smooth crossover at a Z2-critical point. The critical quark mass corresponding to this point has been examined with Nf=2 Wilson fermions for several Nτ in a recent study within our group. For comparison, we also locate the critical point with Nf=2 staggered fermions on Nτ=8 lattices. For this purpose we perform Monte Carlo simulations for several quark mass values and various aspect ratios in order to extrapolate to the thermodynamic limit. The critical mass is obtained by fitting to a finite size scaling formula of the kurtosis of the Polyakov loop. Our results indicate large discretization effects, requiring simulations on lattices with Nτ>8.
In this thesis, we use lattice QCD to study a part of the QCD phase diagram, specifically the QCD phase transition at mu=0, where the QCD matter changes from hadron gas to quark-gluon plasma (QGP) with increasing temperature.
This phase transition takes place as a crossover, but when theoretically changing the masses of the quarks, the order of the phase transition changes as well.
We focus on the region of heavy quark masses with Nf=2 flavours, where we investigate the critical quark mass at the second order phase transition in the form of a Z2 point between the first-order and the crossover region.
The first-order region is positioned at infinitely heavy quarks. As the quark masses decrease, the associated Z3 centre symmetry breaks explicitly, causing the first-order phase transition to weaken until it turns into the Z2 point and finally into a crossover.
We study this Z2 point using simulations at Nf=2 and lattices of the sizes Nt = {6, 8, 10, 12}, partially building on previous work, in which the simulations for Nt = {6, 8, 10} were started.
The simulations for Nt=12 are not finished yet though, but we were able to draw some preliminary conclusions. These simulations are run on GPUs and CPUs, using the codes Cl2QCD and open-QCD-FASTSUM, respectively. Afterwards, the data goes through a first analysis step in the form of the Python program PLASMA, preparing it for the two techniques we use to analyse the nature of the phase transition.
As a first, reliable analysis method, we perform a finite size scaling analysis of the data to find the location of the Z2 point. Since we are using lattice QCD, performing a continuum extrapolation is necessary to reach the continuum result.
In regard to this, the finite size scaling analysis method is hampered by the excessive amount of simulated data that is needed regarding statistics and the total number of simulations, which is why this thesis is only an intermediate step towards the continuum limit.
This also leads to the second analysis technique we explore in this thesis.
We start to design a Landau theory which describes the phase boundary for heavy masses at Nf=2 based on the simulated data.
We develop a Landau functional for every Nt we have simulation data for.
Albeit the results are not at the same precision as the ones from the finite size scaling analysis, we are able to reproduce the position of the Z2 point for every Nt.
Even though we are not able to take a continuum extrapolation right now, after more development takes place in future works, this approach might, in the long run, lead to a continuum result that won't need as many simulations as the finite size scaling analysis.
The QCD phase diagram as a function of temperature, T, and chemical potential for baryon
number, mB, is still unknown today, due to the sign problem, which prohibits direct Monte Carlo
simulations for non-vanishing baryon density. Investigations in models sharing chiral symmetry
with QCD predict a phase diagram, in which the transition corresponds to a smooth crossover at
zero density, but which is strengthened by chemical potential to turn into a first order transition
beyond some second order critical point. This contribution reviews the lattice evidence in favour
and against the existence of a critical point.
In this thesis, we study some features of the quantum chromodynamics (QCD) phase diagram at purely imaginary chemical potential using lattice techniques. This is one of the possible methodologies to get insights about the situation at finite density, where the sign problem prevents direct investigations from first principles.
We focus, in particular, on the Roberge-Weiss plane, where the phase structure with two degenerate flavours is studied both in the light and in the heavy quark mass limit. On the lattice, any result is affected by cut-off effects and so are the positions of the two tricritical points m_{tric}^{1,2} separating the second-order intermediate mass region from the first-order triple light and heavy mass regions. Therefore, changing the lattice spacing 'a', the values of m_{tric}^1 and m_{tric}^2 will change. In order to find their position in the continuum limit – i.e. for 'a' going to 0 – they have to be located on finer and finer lattices. Typically, in lattice QCD (LQCD) simulations, the temperature T is tuned through the bare coupling β, on which 'a' depends, while keeping Nt fixed. Hence, it is common to implicitly refer to how fine the lattice is just mentioning its temporal extent.
Using both Wilson and staggered fermions, we simulate Nf=2 QCD on Nt=6 lattices, varying the quark bare mass from the chiral (m_{u,d} going to 0) to the quenched (m_{u,d} going to infinity) limit. For each quark mass, a thorough finite scaling analysis is carried out, taking advantage of two different but consistent methods. In this way we identify the order of the phase transition locating, then, the position of the tricritical points. In order to convert our measurements to physical units we fix the scale measuring the lattice spacing as well as the pion mass corresponding to the quark bare mass used. This allows a comparison between different discretisation, getting a first idea of how serious are cut-off effects.
To be able to make a comparison between two different discretisations, we added an RHMC algorithm with staggered fermions to the CL2QCD software, a GPU code based on OpenCL, which we released in 2014. A considerable part of our work has been invested in ameliorating and optimising CL2QCD, as well as in developing new analysis tools regularly used next to it. Just to mention one, the multiple histogram method has been implemented in a completely general way and we took advantage of it in order to obtain more precise results. Finally, in order to efficiently handle and monitor the hundreds of simulations that are typically concurrently run in finite temperature LQCD, a completely new Bash library of tools has been developed. We plan to release it as a byproduct of CL2QCD in the near future.
I review recent developments in determining the QCD phase diagram by means of lattice simulations.
Since the invention of methods to side-step the sign problem a few years ago, a number
of additional variants have been proposed, and progress has been made towards understanding
some of the systematics involved. All available techniques agree on the transition temperature
as a function of density in the regime mq/T <~1. There are by now four calculations with signals
for a critical point, two of them at similar parameter values and with consistent results. However,
it also emerges that the location of the critical point is exceedingly quark mass sensitive. At the
same time sizeable finite volume, cut-off and step size effects have been uncovered, demanding
additional investigations with exact algorithms on larger and finer lattices before quantitative conclusions
can be drawn. Depending on the sign of these corrections, there is ample room for the
eventual phase diagram to look as expected or also quite different, with no critical point at all.
In high multiplicity nucleus-nucleus collisions baryon-antibaryon annihilation and regeneration occur during the final hadronic expansion phase, thus distorting the initial equilibrium multiplicity ratios. We quantify the modifications employing the hybrid UrQMD transport model and apply them to the grand canonical partition functions of the Statistical Hadronization Model(SHM). We analyze minimum bias and central Pb+Pb collision data at SPS and LHC energy. We explain the Pion to Proton ratio puzzle. We also reproduce the deuteron to proton ratio at LHC energy by the SHM, and by UrQMD after attaching a phase space coalescence process. We discuss the resulting (T,μB) diagram.
We developed a three-center phenomenological model,able to explain qualitatively the recently obtained experimental results concerning the quasimolecular stage of a light-particle accompanied fission process. It was derived from the liquid drop model under the assumption that the aligned configuration, with the emitted particle between the light and heavy fragment, is reached by increasing continuously the separation distance, while the radii of the heavy fragment and of the light particle are kept constant. In such a way,a new minimum of a short-lived molecular state appears in the deformation energy at a separation distance very close to the touching point. This minimum allows the existence of a short-lived quasi-molecular state, decaying into the three final fragments.The influence of the shell effects is discussed. The half-lives of some quasimolecular states which could be formed in the $^{10}$Be and $^{12}$C accompanied fission of $^{252}$Cf are roughly estimated to be the order of 1 ns, and 1 ms, respectively.
We study anisotropic fluid dynamics derived from the Boltzmann equation based on a particular choice for the anisotropic distribution function within a boost-invariant expansion of the fluid in one spatial dimension. In order to close the conservation equations we need to choose an additional moment of the Boltzmann equation. We discuss the influence of this choice of closure on the time evolution of fluid-dynamical variables and search for the best agreement to the solution of the Boltzmann equation in the relaxation-time approximation.
In this thesis we investigate the role played by gauge fields in providing new observable signatures that can attest to the presence of color superconductivity in neutron stars. We show that thermal gluon fluctuations in color-flavor locked superconductors can substantially increase their critical temperature and also change the order of the transition, which becomes a strong first-order phase transition. Moreover, we explore the effects of strong magnetic fields on the properties of color-flavor locked superconducting matter. We find that both the energy gaps as well as the magnetization are oscillating functions of the magnetic field. Also, it is shown that the magnetization can be so strong that homogeneous quark matter becomes metastable for a range of parameters. This points towards the existence of magnetic domains or other types of magnetic inhomogeneities in the hypothesized quark cores of magnetars. Obviously, our results only apply if the strong magnetic fields observed on the surface of magnetars can be transmitted to their inner core. This can occur if the superconducting protons expected to exist in the outer core form a type-I I superconductor. However, it has been argued that the observed long periodic oscillations in isolated pulsars can only be explained if the outer core is a type-I superconductor rather than type-I I. We show that this is not the only solution for the precession puzzle by demonstrating that the long-term variation in the spin of PSR 1828-11 can be explained in terms of Tkachenko oscillations within superfluid shells.
Stopping power and thermalization in relativistic heavy ion collisions is investigated employing the quantum molecular dynamics approach. For heavy systems stopping of the incoming nuclei is predicted, independent of the energy. The influence of the quantum effects and their increasing importance at low energies, is demonstrated by inspection of the mean free path of the nucleons and the n-n collision number. Classical models, which neglect these effects, overestimate the stopping and the thermalization as well as the collective flow and squeeze out. The sensitivity of the transverse and longitudinal momentum transfer to the in-medium cross section and to the pressure is investigated.
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.
The quark gluon plasma produced in heavy ion collisions behaves like an almost ideal fluid described by viscous hydrodynamics with a number of transport coefficients. The second order coefficient κ is related to a Euclidean correlator of the energy-momentum tensor at vanishing frequency and low momentum. This allows for a lattice determination without maximum entropy methods or modelling, but the required lattice sizes represent a formidable challenge. We calculate κ in leading order lattice perturbation theory and simulations on 1203 × 6, 8 lattices with a < 0.1 fm. In the temperature range 2Tc − 10Tc we find κ = 0.36(15)T2. The error covers both a suitably rescaled AdS/CFT prediction as well as, remarkably, the result of leading order perturbation theory. This suggests that appropriate noise reduction methods on the lattice and NLO perturbative calculations could provide an accurate QCD prediction in the near future.
The Compressed Baryonic Matter (CBM) experiment [1] is a fixed target heavy-ion experiment that will operate at the international Facility for Antiproton and Ion Research (FAIR) [2] now under construction in Darmstadt, Germany. The experiment intends to study rare probes, which are emitted from heavy ion collisions with a beam energy of 4 to 45 AGeV. A focus is laid to the short lived open charm particles and to particles decaying into di-lepton pairs. Handling the up to 107 Au+Au collisions/s required for generating those probes with sufficient statistics, as much as reaching the required sensitivity for observing them, forms a major challenge for the silicon detectors of the experiment. We present the concept and the development status of two central detectors of CBM, the CMOS pixel based micro vertex detector (MVD) and the micro-strip detector based silicon tracking system (STS).
22nd International Workshop on Vertex Detectors, 15-20 September 2013 Lake Starnberg, Germany
In this thesis, different physical and electrical aspects of silicon microstrip sensors and low-mass multi-line readout cables have been investigated. These silicon microstrip sensors and readout cables will be used in the Silicon Tracking System (STS) of the fixed-target heavy-ion Compressed Baryonic Matter (CBM) experiment which is under development at the upcoming Facility for Antiproton and ion Research (FAIR) in Darmstadt, Germany. The highly segmented low-mass tracking system is a central CBM detector system to resolve the high tracking densities of charged particles originating from beam-target interactions. Considering the low material budget requirement the double-sided silicon microstrip detectors have been used in several planar tracking stations. The readout electronics is planned to be installed at the periphery of the tracking stations along with the cooling system. Low-mass multi-line readout cables shall bridge the distance between the microstrip sensors and the readout electronics. The CBM running operational scenario suggests that some parts of the tracking stations are expected to be exposed to a total integrated particle fluence of the order of 1e14 neq/cm2. After 1e14 neq/cm2 the damaged modules in the tracking stations will be replaced. Thus radiation hard sensor is an important requirement for the sensors. Moreover, to cope with the high reaction rates, free-streaming (triggerless) readout electronics with online event reconstruction must be used which require high signal-to-noise (SNR) ratio (i.e., high signal efficiency, low noise contributions). Therefore, reduction in noise is a major goal of the sensor and cable development.
For better insight into the different aspects of the silicon microstrip sensors and multi-line readout cables, the simulation study has been performed using SYNOPSYS TCAD tools. 3D models of the silicon microstrip sensors and the readout cables were implemented which is motivated by the stereoscopic construction of the silicon microstrip sensors. For the evaluation of the performance of the silicon microstrip sensors in the harsh radiation environment during experimental operation, a radiation damage model has been included. It reproduces the behavior of the irradiated CBM prototype sensors. In addition to the static characteristics, the interstrip parameters relevant to understand strip isolation and cross-talk issues have been extracted. The transient simulations have been performed to estimate the charge collection performance of the irradiated sensors. The signal transmission in the readout cables has been evaluated with the finite element simulation tool RAPHAEL. Based on the performance of the front-end electronics used for early prototyping in the CBM experiment, capacitive and resistive noise contributions from the silicon microstrip sensors and multi-line readout cables have been extracted.
To validate the aforementioned simulations, numerous tests have been performed both on the multi-line readout cables and silicon microstrip sensors. Characterizations of multi-line readout cables and silicon microstrip sensors in laboratory conditions have been found to agree reasonably well with the simulations. Considering the expected radiation environment the behavior of silicon microstrip sensors have been studied especially in terms of noise and charge collection efficiency. Source-scan of the silicon microstrip sensors using 241Am is presented. In order to test a first system of detector stations including the data acquisition system, slow control and online monitoring software and for track reconstruction, in-beam tests have been performed at the COSY synchrotron of the Research Center Juelich, Germany. Further, different design parameters have been suggested to improve the sensor and readout cable design on the basis of the simulations and the measurements. Many of these parameters have been implemented in the new prototypes under production. These new prototypes will be tested in-beam by the end of 2013.
Charmonium production in heavy ion collisions is considered as an important diagnostic probe for studying the phase diagram of strongly interacting matter for potential phase transitions. The interpretation of existing data from the CERN SPS is hampered by a lack of knowledge on the properties of open charm particle production in the fireball. Moreover, open charm production in heavy ion collisions by itself is poorly understood. To overcome this obstacle, the NA61/SHINE was equipped with a Small Acceptance Vertex Detector (SAVD), which is predicted to make the experiment sensitive to open charm mesons produced in A-A collisions at the SPS top energy. This paper will introduce the concept and the hardware of the SAVD. Moreover, first running experience as obtained in a commissioning run with a 150 AGeV/c Pb+Pb collision system will be reported.
We compute the static-light baryon spectrum with Nf = 2 flavors of sea quarks using Wilson twisted mass lattice QCD. As light valence quarks we consider quarks, which have the same mass as the sea quarks with corresponding pion masses in the range 340MeV<∼ mPS<∼ 525MeV, as well as partially quenched quarks, which have the mass of the physical s quark. We extract masses of states with isospin I = 0,1/2,1, with strangeness S = 0,−1,−2, with angular momentum of the light degrees of freedom j = 0,1 and with parity P = +,−. We present a preliminary extrapolation in the light u/d and an interpolation in the heavy b quark mass to the physical point and compare with available experimental results.
Strangeness enhancement is discussed as a feature specific to relativistic nuclear collisions which create a fireball of strongly interacting matter at high energy density. At very high energy this is suggested to be partonic matter, but at lower energy it should consist of yet unknown hadronic degrees of freedom. The freeze-out of this high density state to a hadron gas can tell us about properties of fireball matter. The hadron gas at the instant of its formation captures conditions directly at the QCD phase boundary at top SPS and RHIC energy, chiefly the critical temperature and energy density.
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.
At GSI a new, superconducting (sc) continuous wave (cw) LINAC is under design in cooperation with the Institute for Applied Physics (IAP) of Frankfurt University and the Helmholtz Institut Mainz (HIM). This proposed LINAC is highly requested by a broad community of future users to fulfill the requirements of nuclear chemistry, nuclear physics, and especially in the research field of Super Heavy Elements (SHE). In this context the preliminary layout of the LINAC has been carried out by IAP. The main acceleration of up to 7.3 AMeV will be provided by nine sc Crossbar-H-mode (CH) cavities operated at 217 MHz. Currently, a prototype of the cw LINAC as a demonstrator is under development. The demonstrator comprises a sc CH-cavity embedded between two sc solenoids mounted in a horizontal cryomodule. A full performance test of the demonstrator in 2013/14 by injecting and accelerating a beam from the GSI High Charge Injector (HLI) is one important milestone of the project. The status of the demonstrator is presented.
This work derives the value of the neutron capture cross section of 60Fe at the energy of kT = 25 meV. Iron plays an important role in stellar nucleosynthesis, because it is a seed material for the s-process, a neutron capture process in which the elements between iron and bismuth are synthesized.
To determine the thermal neutron cross section of 60Fe, an iron sample produced in the framework of the ERAWAST1 program at the Paul Scherrer Institute in Switzerland was irradiated at the research reactor TRIGA2 at Johannes Gutenberg University in Mainz, Germany. Before the irradiation, the number of 60Fe particles in the sample was calculated using the decay scheme of 60Fe. There were (8.207 ± 0:066 stat 0:298 syst) * 10 14 60Fe particles in the sample.
The irradiation of the sample took place in May 2012. The counting of the reaction product, 61Fe, was undertaken using a HPGe detector located in a laboratory at Johannes Gutenberg University in Mainz. Knowing the number of 60Fe particles in the sample, the number of produced 61Fe particles and the neutron flux from the reactor, the thermal neutron capture cross section of ρth60Fe = (0.203 ± 0:021 stat 0:024 syst) b could be determined.
The determination of the thermal neutron capture cross section at the energy of kT = 25 meV constitutes to the first at this energy. There was already a measurement of the neutron capture cross section of 60Fe at the energy of kT = 25 keV in Karlsruhe in Germany. The result of the measurement was 25 keV = (9.9 ± 2:8 syst 1:4 stat) mb and was published in the year 2009 [14].
Adding datapoints for the cross section at different energies improves extarpolation and helps verification of theoretical models for elemental synthesis. For this reason, a measurement of the 60Fe neutron capture cross section at the energy of kT = 90 keV is planned at Goethe University Frankfurt, Germany.
Having the neutron capture cross section of 60Fe at the energy of kT = 25 keV measured in the year 2009 in Karlsruhe [14], at the energy of kT = 25 meV measured in May 2012 at Johannes Gutenberg University in Mainz and at the planned energy of kT = 90 keV at Goethe University Frankfurt, there will be three points for the extrapolation of the values for the neutron capture cross section of 60Fe. This will lead to a significant reduction in uncertainty with respect to existing theoretical discrepancies.
Subject of this thesis is the non-perturbative investigation of the thermal transition in Quantum Chromodynamics by means of lattice gauge theory and a particular type of lattice fermions, the so-called twisted mass fermions. These fermions offer the possibility of improvement as compared to the standard Wilson-type formulation. We investigate the properties of these fermions at finite temperature, i.e. the structure of the bare parameter space as well as leading order cutoff effects in the weak coupling limit. Then we focus on two-flavour simulations at finite pion mass. We identify the (pseudo-)critical temperatures for our set of pion masses (300 to 500 MeV) and discuss the extrapolation to the chiral limit for which the nature of the transition is still an open question. Besides pseudo-critical temperatures we consider the magnetic equation of state and screening observables. We find that the assumption of a second order transition (in the 3d O(4) universality class) agrees with our data without being able to exclude alternatives. Finally, we discuss the future inclusion of strange and charm quarks in dynamical twisted mass simulations and look at the corresponding cutoff effects in the free limit.
During collisions of heavy ions with heavy targets below the Coulomb barrier, adiabatic molecular orbitals are formed for the inner electrons. Deviations from adiabaticity lead to coupling between various states and can be treated by time-dependent perturbation theory. For high charges ( Z1+Z2 ≧ 60) the molecular electrons are highly relativistic. Therefore, the Dirac equation has to be used to obtain the energies and wave functions. The Dirac Hamiltonian is transformed into the intrinsic rotating coordinate system where prolate spheroidal coordinates are introduced. A set of basis functions is proposed which allows the evaluation of all matrix elements of the Dirac Hamiltonian analytically. The resulting matrix is diagonalized numerically. The finite nuclear charge distribution is also taken into account. Results are presented and discussed for various characteristic systems, e. g. Br-Br, Ni-Ni, I-I, Br-Zr, I-Au, U -U, etc.
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 Projectile Spectator Detector (PSD) of the CBM experiment at the future FAIR facility is a compensating lead-scintillator calorimeter designed to measure the energy distribution of the forward going projectile nucleons and nuclei fragments (reaction spectators) produced close to the beam rapidity. The detector performance for the centrality and reaction plane determination is reviewed based on Monte-Carlo simulations of gold-gold collisions by means of four different heavy-ion event generators. The PSD energy resolution and the linearity of the response measured at CERN PS for the PSD supermodule consisting of 9 modules are presented. Predictions of the calorimeter radiation conditions at CBM and response measurement of one PSD module equipped with neutron irradiated MPPCs used for the light read out are discussed.
The width of the ω meson in cold nuclear matter is computed in a hadronic many-body approach, focusing on a detailed treatment of the medium modifications of intermediate πρ states. The π and ρ propagators are dressed by their self-energies in nuclear matter taken from previously constrained many-body calculations. The pion self-energy includes Nh and Δh excitations with short-range correlations, while the ρ self-energy incorporates the same dressing of its 2π cloud with a full 3-momentum dependence and vertex corrections, as well as direct resonance-hole excitations; both contributions were quantitatively fit to total photo-absorption spectra and πN→ρN scattering. Our calculations account for in-medium decays of type ωN→πN(⁎),ππN(Δ), and 2-body absorptions ωNN→NN(⁎),πNN. This causes deviations of the in-medium ω width from a linear behavior in density, with important contributions from spacelike ρ propagators. The ω width from the ρπ cloud may reach up to 200 MeV at normal nuclear matter density, with a moderate 3-momentum dependence. This largely resolves the discrepancy of linear T–ϱ approximations with the values deduced from nuclear photoproduction measurements.
The phenomenon of magnetism has been known to humankind for at least over 2500 years and many useful applications of magnetism have been developed since then, starting from the compass to modern information storage and processing devices. While technological applications are an important part of the continuing interest in magnetic materials, their fundamental properties are still being studied, leading to new physical insights at the forefront of physics. The magnetism of magnetic materials is a pure quantum effect due to the electrons that carry an intrinsic spin of 1/2. The physics of interacting quantum spins in magnetic insulators is the main subject of this thesis.We focus here on a theoretical description of the antiferromagnetic insulator Cs2CuCl4. This material is highly interesting because it is a nearly ideal realization of the two-dimensional antiferromagnetic spin-1/2 Heisenberg model on an anisotropic triangular lattice, where the Cu(2+) ions carry a spin of 1/2 and the spins interact via exchange couplings. Due to the geometric frustration of the triangular lattice, there exists a spin-liquid phase with fractional excitations (spinons) at finite temperatures in Cs2CuCl4. This spin-liquid phase is characterized by strong short-range spin correlations without long-range order. From an experimental point of view, Cs2CuCl4 is also very interesting because the exchange couplings are relatively weak leading to a saturation field of only B_c=8.5 T. All relevant parts of the phase diagram are therefore experimentally accessible. A recurring theme in this thesis will be the use of bosonic or fermionic representations of the spin operators which each offer in different situations suitable starting points for an approximate treatment of the spin interactions. The methods which we develop in this thesis are not restricted to Cs2CuCl4 but can also be applied to other materials that can be described by the spin-1/2 Heisenberg model on a triangular lattice; one important example is the material class Cs2Cu(Cl{4-x}Br{x}) where chlorine is partially substituted by bromine which changes the strength of the exchange couplings and the degree of frustration.
Our first topic is the finite-temperature spin-liquid phase in Cs2CuCl4. We study this regime by using a Majorana fermion representation of the spin-1/2 operators motivated by theoretical and experimental evidence for fermionic excitations in this spin-liquid phase. Within a mean-field theory for the Majorana fermions, we determine the magnetic field dependence of the critical temperature for the crossover from spin-liquid to paramagnetic behavior and we calculate the specific heat and magnetic susceptibility in zero magnetic field. We find that the Majorana fermions can only propagate in one dimension along the direction of the strongest exchange coupling; this reduction of the effective dimensionality of excitations is known as dimensional reduction.
The second topic is the behavior of ultrasound propagation and attenuation in the spin-liquid phase of Cs2CuCl4, where we consider longitudinal sound waves along the direction of the strongest exchange coupling. Due to the dimensional reduction of the excitations in the spin-liquid phase, we expect that we can describe the ultrasound physics by a one-dimensional Heisenberg model coupled to the lattice degrees of freedom via the exchange-striction mechanism. For this one-dimensional problem we use the Jordan-Wigner transformation to map the spin-1/2 operators to spinless fermions. We treat the fermions within the self-consistent Hartree-Fock approximation and we calculate the change of the sound velocity and attenuation as a function of magnetic field using a perturbative expansion in the spin-phonon couplings. We compare our theoretical results with experimental data from ultrasound experiments, where we find good agreement between theory and experiment.
Our final topic is the behavior of Cs2CuCl4 in high magnetic fields larger than the saturation field B_c=8.5 T. At zero temperature, Cs2CuCl4 is then fully magnetized and the ground state is therefore a ferromagnet where the excitations have an energy gap. The elementary excitations of this ferromagnetic state are spin-flips (magnons) which behave as hard-core bosons. At finite temperatures there will be thermally excited magnons that interact via the hard-core interaction and via additional exchange interactions. We describe the thermodynamic properties of Cs2CuCl4 at finite temperatures and calculate experimentally observable quantities, e.g., magnetic susceptibility and specific heat. Our approach is based on a mapping of the spin-1/2 operators to hard-core bosons, where we treat the hard-core interaction by the self-consistent ladder approximation and the exchange interactions by the self-consistent Hartree-Fock approximation. We find that our theoretical results for the specific heat are in good agreement with the available experimental data.
Charmonia with different transverse momentum pT usually comes from different mechanisms in the relativistic heavy ion collisions. This work tries to review the theoretical studies on quarkonium evolutions in the deconfined medium produced in p-Pb and Pb-Pb collisions. The charmonia with high pT are mainly from the initial hadronic collisions, and therefore sensitive to the initial energy density of the bulk medium. For those charmonia within 0.1 < pT < 5 GeV/c at the energies of Large Hadron Collisions (LHC), They are mainly produced by the recombination of charm and anti-charm quarks in the medium. In the extremely low pT ∼ 1/RA (RA is the nuclear radius), additional contribution from the coherent interactions between electromagnetic fields generated by one nucleus and the target nucleus plays a non-negligible role in the J/ψ production even in semi-central Pb-Pb collisions.
We have investigated and interpreted the production cross sections and isotopic distributions of projectile-like residues in the reactions 124Sn + 124Sn and 112Sn + 112Sn at an incident beam energy of 1 GeV/nucleon measured with the FRS fragment separator at the GSI laboratory. For the interpretation of the data, calculations within the statistical multifragmentation model (SMM) for an ensemble of excited sources were performed with ensemble parameters. The possible modification of symmetry energy parameter, in the multifragmentation region at the low density and hot freeze-out environment, is studied. It is reconfirmed that a significant reduction of the symmetry energy term is found necessary to reproduce experimental results at these conditions. We have also found a decreasing trend of the symmetry energy for large neutron-rich fragments of low excitation energy which is interpreted as a nuclear-structure effect.
Die vorliegende Arbeit befallt sich im theoretischen Teil mit den Grundlagen zu Strahl-Resonator-Wechselwirkungen bei Beschleunigerresonatoren und mit den sich daraus ergebenden Konsequenzen bei der Resonatorentwicklung für zukünftige lineare Kollider mit Multibunch-Betrieb. Zur Bekämpfung der vor allem im Multibunchbetrieb störenden Long-Range-Wakefelder müssen die schädlichen Moden möglichst so stark bedämpft werden, daß ihre Felder bis zum Eintreffen des nächsten Bunches auf ein erträgliches Maß abgeklungen sind. Im experimentellen Teil befaßt sich diese Arbeit daher mit der Entwicklung von Meßmethoden zur Bestimmung sehr kleiner Resonatorgüten sowie sehr kleiner transversaler Shuntimpedanzen bzw. sehr kleiner Feldpegel in stark störmodenbedämpften Beschleunigerresonatoren. Diese Meßmethoden sind an mehreren S-Band-Modellresonatoren (Betriebsfrequenz lag bei etwa 2.4 GHz) mit verschiedenen Dämpfungssystemen, die für den Einbau in einen normalleitenden Linearbeschleuniger für einen Kollider geeignet wären, erfolgreich getestet worden. Die Feldmessungen an den Modellresonatoren haben bisher unbekannte Gesetzmäßigkeiten bezüglich des Verhaltens dieser Dämpfungssysteme ergeben. In einer kurzen Beschreibung und Diskussion der sechs wichtigsten Vorschläge für zukünftige lineare Kollider wurde ein Überblick über die Unterschiede bei diesen verschiedenen Konzepten gegeben. Zunächst konnten über eine qualitative Diskussion der beim Linearbeschleuniger vom Iristyp vorkommenden Beam Blowup Phänomene, wie der regenerative BBU und der cumulative BBU, die Erscheinungsformen und die physikalischen Ursachen dieser BBU Phänomene verstanden werden. Hier zeigt sich, daß bei Irisstrukturen die HEM11-Moden die Hauptursache sowohl für den regenerativen- als auch für den cumulativen BBU sind. Der dritte Abschnitt führte in eine allgemeine Methode zur quantitativen Beschreibung der sogenannten Strahl-Resonator-Wechselwirkung ein. Diese Methode heißt Condon- Methode und erlaubt die Berechnung von BBU verursachenden Wakefeldern über eine Eigenwellenentwicklung aus den Eigenmoden des leeren Rersonators. Im vierten Abschnitt wurde durch die Herleitung des Theorems von Panofsky-Wenzel die Theorie der Strahl-Resonator-Wechselwirkung vervollständigt, wonach der einer Testladung während der Durchquerung eines felderfüllten Resonators mitgeteilte Transversalimpuls vollständig durch die räumliche Verteilung der elektrischen Longitudinalkomponente allein bestimmt ist. Damit erhält man also eine Aussage über die Wirkung der in Beschleunigerresonatoren feldanfachenden vorauslaufenden Ladungen auf die nachfolgenden. Dabei konnte auch die Frage geklärt werden, welche Moden zylindrischer Symmetrie wegen ihrer transversal ablenkenden Wirkung für den Teilchenstrahl gefährlich sind. Hier zeigt sich, daß alle BBU verursachenden Moden TM2np- bzw. TM2np-Moden sind, d.h., die Moden mit dipol- bzw. quadrupolartiger Symmetrie. Die Anwendung der in den Abschnitten drei und vier entwickelten Theorie zur Strahl-Resonator-Wechselwirkung konnte im Abschnitt fünf anhand dreier, für die Beschleunigerphysik sehr interessanter Beispiele gezeigt werden. Im ersten Beispiel gelang die Beschreibung der Wechselwirkung eines in Längsrichtung homogenen Strahls, welcher transversal Betatranschwingungen vollführt, mit der TM110-Mode eines Zylinderresonators. Dieses Beispiel ist von praktischer Bedeutung bei Linearbeschleunigern. die bei hohem Duty Cycle betrieben werden, also z.B. beim RACE TRACK Mikrotron oder bei supraleitenden Linacs. Beim zweiten Beispiel hat die Anwendung der Theorie auf eine Irisstruktur zu Formeln geführt, die sich Fair eine numerische Berechnung des Startstroms zum regenerativen BBU eignen, was jedoch relativ aufwendig ist. Es konnte aber auch eine einfache Abschätzungsformel für den Startstrom durch die Anwendung des Poyntingschen Satzes auf eine differentielle Länge des der Irisstruktur entsprechenden Wellenleiters abgeleitet werden. Aus der Bedingung, daß die durch den Strahl erzeugte Leistung pro Längeneinheit gleich den Leistungsverlusten pro Längeneinheit ist, findet man den Startstrom für den regenerativen BBU. Das letzte Beispiel, die Wechs 1 e Wirkung einer hochrelativistischen Punktladung mit einem beliebigen Resonator, ist auch das wichtigste. Hier wurden die Wakefelder aus einer simplen Energiebilanzbetrachtung abgeleitet, da eine Berechnung nach der Condon-Methode relativ aufwendig und langwierig wäre. Diese Vorgehensweise hat hier zu einem tieferen physikalischen Verständnis der Vorgänge im Resonator geführt. Die mit Hilfe einer Punktladung abgeleiteten Wakefelder sind Greensfunktionen. die zur quantitativen Beschreibung des cumulativen BBU’s bei linearen Kollidern benutzt werden können. Die Diskussion der anhand der Beispiele gewonnenen Ergebnisse am Ende des fiinften Abschnitts führte zu verschiedenen Maßnahmen zur Verringerung der schädlichen Strahl-Resonator-Wechselwirkung. Hier hat sich gezeigt, daß sowohl der regenerative BBU als auch der cumulative BBU u. a. durch eine Verringerung der Resonatorgüte der strahlstörenden Dipolmode verhindert werden können. Im sechsten Abschnitt erfolgte die noch ausstehende quantitative Beschreibung des cumulativen BBU mit Hilfe der im vorangehenden Abschnitt am dritten Beispiel gewonnenen Formeln für die Wakefelder. Die Berechnung der Strahlablage und Strahlrichtung geschieht hier über einen Matrizenformalismus, der aus der Idee heraus entstand, die Beschleunigersektionen des linearen Kolliders durch Resonatoren verschwindender Länge zu ersetzen. Uber den Matrizenformalismus konnte die durch den Einfluß von Beschleunigung, Fokussierung und Wakefeldern doch recht komplizierte Teilchenbewegung sehr elegant formuliert werden, jedoch eignet sich dieser Formalismus nur für numerische Zwecke. Abschätzungen sind in diesem allgemeinen Fall unmöglich. Durch die Einführung eines sehr restriktiven Modells, des sogenannten DAISY-CHAIN Modells, welches nur bei sehr stark bedämpften Beschleunigersektionen gültig ist. hat sich der Matrizenformalismus auf sehr einfache, der analytischen Berechnung zugängliche Gleichungen reduzieren lassen. Die Bedämpfung der Beschleunigersektionen muß dabei so stark sein, daß eine Ladung innerhalb einer ganzen Kette äquidistanter Ladungen nur ein signifikantes Wakefeld der unmittelbar vorrauslaufenden Ladung erfährt. Wie stark im Einzelfall bedämpft werden muß, um einen stabilen Transport einer Kette von Teilchenpaketen zu ermöglichen, konnte anhand zweier, in der Betriebsfrequenz unterschiedlicher Konzepte für normalleitende Linearbeschleuniger zukünftiger Kollider gezeigt werden. Dabei wurde deutlich, daß man bei ausschließlicher Anwendung von in Bezug auf die HEM11-pi-Mode stark bedämpften Beschleunigerstrukturen zur Kontrolle des cumulativen BBU bei einer hohen Betriebsfrequenz, z.B. im X-Band (11.45 GHz), sehr unbequem niedrige Gütewerte von ca. Q=5 erreichen muß. Das ist, wie sich im praktischen Teil der vorliegenden Arbeit gezeigt hat, vom technischen Aufwand her gesehen sehr schwierig. Für einen X-Band-Kollider wird man also eine Kombination von Maßnahmen zur Kontrolle des cumulativen BBU’s bevorzugen, z.B. neben dem Bedämpfen auch das sogenannte “Detunen” der Beschleunigersektionen. Bei einem Linearbeschleuniger im S-Band (Betriebsfrequenz bei 3 GHz) befindet man sich von vornherein bei ausschließlicher Verwendung gedämpfter Strukturen in bequemeren Gütebereichen Q ungefähr gleich 20-50, was ohne weiteres praktikabel ist. Aber auch hier kann man durch Zusatzmaßnahmen die Anforderungen an die Resonatordämpfung weiter reduzieren. Als erste Methode zur Bestimmung der Güte eines störmodenbedämpften Beschleunigerresonators wurde die Chipman-Methode angewendet. Meßobjekt war hier das dreizellige Modell einer Irisstruktur mit Halbzellenabschluß. Zur Auskopplung der dominanten Störmode, der sogenannten HEM11-Mode, war die mittlere Irisblende einseitig geschlitzt. Bei diesem Modell lag die Frequenz der als Beschleunigermode vorgesehenen TM010-2pi/3-Mode etwa bei 2.35 GHz und die Frequenz der dominanten Störmode, der HEM11-pi-Mode, lag bei etwa 2.81 GHz. Die mittlere geschlitzte Irisblende war austauschbar, so daß eine Messung der durch das Dämpfungssystem belasteten Güte QL bzw. des Koppelfaktors K in Abhängigkeit von der Schlitzhöhe möglich war. Die Messungen ließen sich bei diesem Koppelsystem ohne Schwierigkeiten durchrühren, bei der größten möglichen Schlitzhöhe von 10 mm wurde auch der größte Koppelfaktor mit 46 gemessen. Bei einer vom Dämpfungssystem unbelasteten Güte von Q0=4500 korrespondiert ein Koppelfaktor von K=46 mit einer durch das Dämpfungssystem belasteten Güte von QL = 100. Ein Mangel wurde bei der Anwendung der Chipman-Methode sofort sichtbar: Durch die Anregung der HEM11-pi-Mode von der Meßleitung aus sind im Koppelsystem offenbar Störmoden angeregt worden. Liegen diese Störmoden nahe bei der zu messenden Resonanz, dann ist eine präzise Bestimmung des Koppelfaktors unmöglich. Glücklicherweise war das hier nicht der Fall. Die Messungen mit der einseitig geschlitzten Irisblende haben gezeigt, daß dieses Dämpfungssystem Anwendung finden könnte bei Beschleunigerstrukturen im S-Band. wie sie z.B beim DESY/THD-Kollider vorgeschlagen wurden. Natürlich kann bei den hier erreichten Koppelfaktoren nicht die Dämpfung der schädlichen HEM11-pi- Mode die alleinige Maßnahme sein, die einseitig geschlitzte Irisblende könnte nur zusammen mit dem Detunen angewendet werden. Da die einseitig geschlitzte Irisblende auch eine Feldasymmetrie bei der Beschleunigermode erzeugt, müssen die Dämpfer entlang einer Beschleunigersektion alternierend angebracht werden, d.h. jeder Dämpfer ist im Bezug zum nächsten Nachbardämpfer um 90° gedreht. Die 90° ergeben sich aus der Notwendigkeit, auch die Dämpfung der zweit en Polarisationsebene der HEM11-pi-Mode zu gewährleisten. Als zweite, der Chipman-Methode sehr ähnliche Methode, wurde die Kurzschlußschiebermethode angewendet. Erstes Untersuchungsobjekt war die bei der Chipman- Methode bereits erwähnte dreizeilige Irisstruktur. Ein Vorteil im Vergleich zur Chipman-Methode ist vor allem die schnelle Durchführbarkeit der Messung bei wenig experimentellem Aufwand, wenn auch die Kurzschlußschiebermethode weniger präzise ist, und man auf einige Informationen, wie z.B. der Verlauf des Reflexionsfaktors und dessen Phase, verzichten muß. Im Vergleich mit der Chipman-Methode waren die mit der Kurzschlußschiebermethode gemessenen Koppelfaktoren immer um etwa 10-15% höher. Das liegt vor allem daran, daß die Theorie zur Kurzschlußschiebermethode von einem verlustfreien Resonator-Hohlleitersystem ausgeht, so daß die nach dieser Theorie ermitteten Koppelfaktoren prinzipiell zu groß sind. Auch bei dieser Methode hat sich gezeigt, daß eine Auswertung der Meßergebnisse scheitern muß, falls ein Modenüberlapp auftritt. Bei Experimenten mit komplizierteren Dämpfungssystemen, bestehend aus mehr als vier Hohlleitern an Resonatoren mit mehr als zwei Zellen ist deutlich geworden, daß eine Bestimmung des Koppelfaktors über die Kurzschlußschiebermethode durch die entstehende Modenvielfalt praktisch unmöglich ist. Es stellte sich heraus, daß bei der Auswertung der Meßergebnisse dadurch ein Fehler entsteht, wenigstens bei sehr starker Dämpfung, daß man die Feldverteilung als konstant animmt, denn bei dem Vergleich der unbelasteten Güte Q0 mit der vom Dämpfungssystem belasteten Güte QL geht man davon aus, daß die Feldverteilungen im ungedämpften- und gedämpften Fall identisch sind. Das kann bei Koppelfaktoren im Bereich von einigen zehn bis zu einigen hundert nicht mehr zutreffen, da das Feld der Mode immer stärker in das Dämpfungssystem eindringt, je stärker die Kopplung ist. Das ändert die Modengeometrie natürlich in dramatischer Weise und die belastete Güte QL kann dann nicht mehr einfach über die Gleichung QL=Q0/(1+ K) aus den gemessenen Größen Q, und K ausgerechnet werden, da der Koppelfaktor K nun nicht mehr konstant sein kann, sondern im Gegenteil sich sehr stark ändert, je nachdem an welcher Stelle die Felder gemessen werden. Ein weiterer Mangel bei beiden Methoden ist, daß über diese Methoden weder die longitudinale noch die transversale Shuntimpedanz bestimmt werden kann. Ein Ausweg aus diesem Dilemma war die Anwendung zweier neuer Meßmethoden, die Antennenmethode und die nichtresonante Störkörpermethode. Diese beiden Methoden beruhen im Gegensatz zu den ersten beiden Methoden auf einer direkten Bestimmung der Feldpegel bzw. der transversalen Shuntimpedanz im bedämpften Resonator was den Vorteil hat, daß im Resonator genau das Feld bzw. die Shuntimpedanz vermessen wird, welches die Teilchen bei der Durchquerung des Resonators auch tatsächlich sehen. Die Antennenmethode war eine komplette Neuentwicklung, während es sich bei der nichtresonante Störkörpermethode um die Anwendung einer seit 1966 bekannten, jedoch in Vergessenheit geratenen Theorie handelte. Beide Meßmethoden konnten am Beispiel eines im Bezug auf die TM110-Mode (Frequenz bei ca. 3.2 GHz) sehr stark bedämpften Zylinderresonators (Die Frequenz der TM010-Mode lag bei ca. 2.049 GHz) erfolgreich getestet werden. Die durch das Dämpfungssystem belastete Güte QL war hier ca. 10. Bei der Bestimmung der longitudinalen elektrischen Feldstärken bzw. der longitudinalen Shuntimpedanz der TM110-Mode in Abhängigkeit vom axialen Abstand vor und nach der Bedämpfung konnten zunächst folgende Feststellungen gemacht werden: 1) Die Modengeometrie im ungedämpften- und gedämpften Fall unterscheiden sich sehr stark voneinander. Dadurch mißt man verschiedene Koppelfaktoren, je nachdem an welcher Stelle man die Felder mißt. 2) der maximal gemessene Koppelfaktor liefert über die Gleichung QL=Q0/(1+K) die richtige beklastete Güte QL. 3) Der höchste Koppelfaktor wurde bei der Feldmessung in einem Achsortabstand vom halben Radius des Zylinderresonators gemessen. Da die beiden Meßmethoden das Verhältnis der elektrischen Feldstärkequadrate in Abhängigkeit vom Meßort vor und nach der Bedämpfung liefern, konnte die zweite Feststellung nur durch eine Kontrollmessung mit Hilfe der Kurzschlußschiebermethode, die hier dank des einfachen Aufbaus leicht durchfiihrbar war, gemacht werden. Die Kurzschlußschiebermessung lieferte eine Güte QL ungefähr gleich 9, während der höchste bzw. der niedrigste mit den beiden neuen Megmethoden ermittelte Koppelfaktor mit einer Güte von QL ungefähr gleich 11 bzw. mit einer Güte von QL ungefähr gleich 14 korrespondierte, d.h. also. daß der höchste gemessene Koppelfaktor für dieses Dämpfungssystem die richtige Resonatorgüte liefert. Anhand eines zweizeiligen Resonators (Die Frequenz der TM010-2pi/3-Beschleunigermode lag bei ca. 2.35 GHz) mit beidseitig geschlitzter Irisblende als Dämpfungssystem für die HEM11-pi-Mode (ca. 3.5 GHz) konnte gezeigt werden, daß die zweite Feststellung eine Gesetzmäßigkeit bei spiegelsymmetrischen Dämpfungssystemen ist. Im Unterschied zum Zylinderresonator wurde der höchste mit der richtigen bedämpften Güte QL ungefähr gleich 37 korrespondierend Koppelfaktor K ungefähr gleich 153 jedoch direkt auf der Resonatorachse gemessen. Die bedämpfte Güte wurde auch hier wieder mit Hilfe der Kurzschlußschiebermethode kontrolliert. Ein sehr interessantes Verhalten zeigte der gleiche zweizeilige Resonator mit einseitig geschlitzter Irisblende als Dämpfungssystem. Hier korrespondierte der in der Nähe der Resonatorwand gemessene niedrigste Koppelfaktor mit der bedämpften Güte QL ungefähr gleich 230 des Resonators. In Achsennähe hingegen war der Koppelfaktor etwa dreimal höher, K ungefähr gleich 82, als aus der der Güteerniedrigung K ungefähr gleich 35 nach der Dämpfung hervorgegangen wäre, die transversale Shuntimpedanz ist also auch etwa um den Faktor 3 erniedrigt. Durch dieses Verhalten ist der einseitig bedämpfte Resonator für die Verwendung bei einem linearen Kollider im S-Band (hier muß nicht so stark bedämpft werden) interessant geworden, denn wenn nur wenige Zellen einer Beschleunigersektion mit einem Dämpfungssystem ausgerüstet werden müssen, ist es wichtig in diesen Zellen ein effektives Dämpfungssystem bei Gewährleistung eines einwandfreien Transports der Feldenergie der HEM11-pi-Mode in diese gedämpften zu haben. Das funktioniert einerseits nur, wenn sich die Resonanzfrequenz der gedämpften Zellen in Bezug auf die HEM11-pi-Mode auf die Resonanzfrequenz der benachbarten ungedämpften Zellen einstellen läßt und andererseits die mit einer Dämpfung einhergehende schlechtere Anregungsfähigkeit dieser Störmode in den gedämpften Zellen nicht zu schlecht ist. Bei einer zu starken Dämpfung wäre beides nicht möglich. Zusammenfassend kann man sagen, daß durch die Antennen- und die nichtresonante Störkörpermethode ein für die Entwicklung von störmodenbedämpften Beschleunigerresonatoren für zukünftige lineare Kollider und natürlich auch anderer Elektronenbeschleuniger sehr wirksames Instrument zur Verfügung steht. Ein detailliertes Design eines für einen bestimmten Beschleuniger passenden Dämpfungssystems ist mit Hilfe dieser Meßmethoden möglich geworden, da kleine Unterschiede zwischen verschiedenen Ausführungen von Dämpfungssystemen meßbar sind. Durch die bei der Anwendung der Meßmethoden auf unterschiedliche bedämpfte Resonatoren gefundenen Gesetzmäßigkeiten ist unter anderem auch die Frage geklärt worden, auf welche Weise ein Dämpfungssystem auch auf numerischem Wege mit Hilfe von Computerprogrammen wie z.B. MAFIA berechnet werden kann.
With the mass asymmetry described by the dynamical collective fragmentation coordinate ξ, and with use of the asymmetric two-center shell model, the fission mass distributions for 226Ra, 236U, and 258Fm (which are typical representatives for triple-, double-, and single-humped distributions) are explained.
The mechanisms of spontaneous and induced emission of radiation are derived from the Dirac equation in a rotating coordinate system. The molecular-orbital x-ray spectra exhibit a strong asymmetry with respect to the beam axis. The asymmetry peaks for the high-energy transitions, which can be used for spectroscopy of two-center orbitals.
Twisted heterostructures of van der Waals materials have received much attention for their many remarkable properties. Here, we present a comprehensive theory of the long-range ordered magnetic phases of twisted bilayer α-RuCl3 via a combination of first-principles calculations and atomistic simulations. While a monolayer exhibits zigzag antiferromagnetic order with three possible ordering wave vectors, a rich phase diagram is obtained for moiré superlattices as a function of interlayer exchange and twist angle. For large twist angles, each layer spontaneously picks a single zigzag ordering wave vector, whereas, for small twist angles, the ground state involves a combination of all three wave vectors in a complex hexagonal domain structure. This multi-domain order minimizes the interlayer energy while enduring the energy cost due to the domain wall formation. Our results indicate that magnetic frustration due to stacking-dependent interlayer exchange in moiré superlattices can be used to tune the magnetic ground state and enhance quantum fluctuations in α-RuCl3.
The theory of nucleon transfer in heavy ion reactions is formulated on the basis of the molecular particlecore model for a system consisting of two cores and one extracore nucleon. The extracore nucleon is described by the molecular wave functions of the asymmetric two-center shell model. The cores, which are assumed to be collectively excitable, are treated with vibrator-rotator models. Potentials for shape polarization are contained in the asymmetric two-center shell model and the interaction between the cores. The excitation and transfer of the extracore nucleon is induced by the radial and rotational couplings. The coupled channel equations, which include the recoil effects in first approximation, are derived in a form suitable for numerical calculations of cross sections. NUCLEAR REACTIONS Heavy ion scattering, theory of nucleon transfer, molecular wave functions, two-center shell model, collective and single-particle excitation.
In the present work, the problem of protein folding is addressed from the point of view of equilibrium thermodynamics. The conformation of a globular protein in solution at common temperatures is quite complicated without any geometrical symmetry, but it is an ordered state in the sense of its biological activity. This complicated conformation of a single protein molecule is destroyed upon increasing the temperature or by the addition of appropriate chemical agents, as is revealed by the loss of its activity and change of the physical properties, and so on. Once the complicated native structures having biological activity are lost, it would be natural to suppose that the native structure could hardly be restored. Nevertheless, pioneers, such as Anson and Mirsky, recognized as early as in 1925 that this was not always the case. If one defines the folded and unfolded states of a protein as two distinct phases of a system, then under the variation of temperature the system is transformed from one phase state into another and vice versa. The process of protein folding is accompanied by the release or absorption of a certain amount of energy, corresponding to the first-oder-type phase transitions in the bulk. Knowing the partition function of the system one can evaluate its energy and heat capacity under different temperatures. This task was performed in this work. The results of the developed statistical mechanics model were compared with the results of molecular dynamic simulations of alanine poylpeptides. In particular, the dependencies on temperature of the total energy of the system and heat capacity were compared for alanine polypeptides consisting of 21, 30, 40, 50 and 100 amino acids. The good correspondence of the results of the theoretical model with the results of molecular dynamics simulations allowed to validate the assumptions made about the system and to establish the accuracy range of the theory. In order to perform the comparison of the results of theoretical model and the molecular dynamics simulations it is necessary to perform the efficient analysis of the results of molecular dynamics simulations. This task was also addressed in the present work. In particular, different ways to obtain dependence of the heat capacity on temperature from molecular dynamics simulations are discussed and the most efficient one is proposed. The present thesis reports the result of molecular dynamic simulations for not only alanine polypeptides by also for valine and leucine polypeptides. In valine and leucine polypeptides, it is also possible to observe the helix↔random coil transitions with the increase of temperature. The current thesis presents a work that starts with the investigation of the fundamental degrees of freedom in polypeptides that are responsible for the conformational transitions. Then this knowledge is applied for the statistical mechanics description of helix↔coil transitions in polypeptides. Finally, the theoretical formalism is generalized for the case of proteins in water environment and the comparison of the results of the statistical mechanics model with the experimental measurements of the heat capacity on temperature dependencies for two globular proteins is performed. The presented formalism is based on fundamental physical properties of the system and provides the possibility to describe the folding↔unfolding transitions quantitatively. The combination of these two facts is the major novelty of the presented approach in comparison to the existing ones. The “transparent” physical nature of the formalism provides a possibility to further apply it to a large variety of systems and processes. For instance, it can be used for investigation of the influence of the mutations in the proteins on their stability. This task is of primary importance for design of novel proteins and drug delivering molecules in medicine. It can provide further insights into the problem of protein aggregation and formation of amyloids. The problem of protein aggregation is closely associated with various illnesses such as Alzheimer and mad cow disease. With certain modifications, the presented theoretical method can be applied to the description of the protein crystallization process, which is important for the determination of the structure of proteins with X-Rays. There many other possible applications of the ideas described in the thesis. For instance, the similar formalism can be developed for the description of melting and unzipping of DNA, growth of nanotubes, formation of fullerenes, etc.
Collisions of very heavy ions at energies close to the Coulomb barrier are discussed as a unique tool to study the behavior of the electron-positron field in the presence of strong external electromagnetic fields. To calculate the excitation processes induced by the collision dynamics, a semiclassical model is employed and adapted to describe the field-theoretical many-particle system. An expansion in the adiabatic molecular basis is chosen. Energies and matrix elements are calculated using the monopole approximation. In a supercritical (Z1+Z2≳173) quasiatomic system the 1s level joins the antiparticle continuum and becomes a resonance, rendering the neutral vacuum state unstable. Several methods of treating the corresponding time-dependent problem are discussed. A projection-operator technique is introduced for a fully dynamical treatment of the resonance. Positron excitation rates in s1/2 and p1/2 states are obtained by numerical solution of the coupled-channel equations and are compared with results from first- plus second-order perturbation theory. Calculations are performed for subcritical and supercritical collisions of Pb-Pb, Pb-U, U-U, and U-Cf. Strong relativistic deformations of the wave functions and the growing contributions from inner-shell bound states lead to a very steep Z dependence of positron production. The results are compared with available data from experiments done at GSI. Correlations between electrons and positrons are briefly discussed.
The RFQ direct injection project (RFQ-DIP) for the neutrino physics experiment IsoDAR aims at an efficient injection of a high-current H²⁺ beam into the dedicated 60 MeV driver cyclotron. Therefore, it is intended to use a compact 32.8 MHz RFQ structure of the split-coaxial type as a pre-buncher. To determine the thermal elongation of the 1.4 m long electrode rods as well as the thermal frequency detuning of the RF structure at a maximum nominal power load of 3.6 kW, an extensive thermal and structural mechanical analysis using COMSOL Multiphysics was conducted. The water heating along the cooling channels as well as the properties of heat transfer from the copper structure to the cooling water were taken into account, which required CFD simulations of the cooling water flow in the turbulent regime. Here we present the methods and results of the sophisticated thermal and structural mechanical simulations using COMSOL and provide a comparison to more simplistic simulations conducted with CST Studio Suite.
We study the effect of thermal charm production on charmonium regeneration in high energy nuclear collisions. By solving the kinetic equations for charm quark and charmonium distributions in Pb+Pb collisions, we calculate the global and differential nuclear modification factors RAA(Npart) and RAA(pt) for J/ψ s. Due to the thermal charm production in hot medium, the charmonium production source changes from the initially created charm quarks at SPS, RHIC and LHC to the thermally produced charm quarks at Future Circular Collider (FCC), and the J/ψ suppression (RAA<1) observed so far will be replaced by a strong enhancement (RAA>1) at FCC at low transverse momentum.
Thermal dilepton radiation from the hot fireballs created in high-energy heavy-ion collisions provides unique insights into the properties of the produced medium. We first show how the predictions of hadronic many-body theory for a melting ρ meson, coupled with quark–gluon plasma emission utilizing a modern lattice-QCD based equation of state, yield a quantitative description of dilepton spectra in heavy-ion collisions at the SPS and the RHIC beam energy scan program. We utilize these results to systematically extract the excess yields and their invariant-mass spectral slopes to predict the excitation function of fireball lifetimes and (early) temperatures, respectively. We thereby demonstrate that future measurements of these quantities can yield unprecedented information on basic fireball properties. Specifically, our predictions quantify the relation between the measured and maximal fireball temperature, and the proportionality of excess yield and total lifetime. This information can serve as a “caloric” curve to search for a first-order QCD phase transition, and to detect non-monotonous lifetime variations possibly related to critical phenomena.
In dieser Arbeit wurden thermodynamische Eigenschaften eines chiralen Quark Meson Modelles untersucht. Das chirale Quark Meson Model beschreibt die starke Wechselwirkung über den Austausch von Mesonen und zudem die thermische und dichteabhängige Entwicklung der Quarkmassen im Medium über die chirale Symmetrie.Im SU(2) Model wurde zunächst in mean field approximation gearbeitet, um im Anschluss den divergenten Vakuumterm mit einzubeziehen. Nach eingehender Untersuchung der Ergebnisse, wurden dann die thermischen Mesonenfluktuationen studiert. In beiden Ansätzen verschiebt die Nullpunktsenergie den chiralen Phasenübergang zu höheren Temperaturen, wodurch die Massen bei höheren Temperaturen entarten. Beide Ansätze wurden dann zu einem gemeinsamen Modell kombiniert, um den Einfluss der Mesonenfluktuationen auf Ordnungsparameter, Massen und thermodynamische Grössen zu untersuchen. Als Fazit der Studie kann behauptet werden, dass sich der Einfluss der Mesonenfluktuationen in grösserem Maÿ auf die Thermodynamik, als auf den Ordnungsparameter und die Massen auswirkt. Im SU(3) Modell wurden ebenfalls regularisiert und zudem Vektormesonen mitberücksichtigt, welche die Repulsion zwischen den einzelnen Freiheitsgraden modelliert. Die Zustandsgleichung wird durch den Vakuum Term etwas softer und zeigt ein ähnliches Verhalten im niederen Energiebereich. Untersucht wurde neben der Temperatur T, die Elektron Baryon Rate Ye, die Sigma Meson Masse noch der Einfluss der Vektorkopplung. Aus der Zustandsgleichung konntendann Isentropen im T-mu Phasendiagramm errechnet werden, welche in naher Zukunft Aufschluss über eine dritte Familie von kompakten Sternen in Zusammenhang mit der entsprechenden Supernova Explosion geben könnte. Um die Existenz von kompakten Sternen genauer zu analysieren, wurde das chiraleSU(3) Quark Meson Modell bei T = 0 benutzt, um über die aus dem Formalismusgewonnenen Grössen Druck und Energiedichte die Tolmann-Oppenheimer-Volkoff zu lösen. Diese stellen die Masse-Radius Beziehungen kompakter Objekte dar. Auf der Suche nach Twin Stern Lösungen aus dem chiralen SU(3) Quark Meson Model wurde zunächst ein Modell für Hybridsterne entwickelt. Im untersuchten Parameterbereich fanden wir Hybrid Stern Lösungen, bei welchen der Einfluss der Quarkmaterie auf die Stabilität des Sternes untersucht wurde, denn das Einsetzen des Phasenüberganges übt einen zusätzlichen gravitativen Zug auf die hadronische Kruste aus. Der Stern ist stabil, wenn der Druck der Quarkmaterie diesem zusätzlichen Zug standzuhalten vermag. Für einen zu grossen Sprung in der Energiedichte werden die Lösungen jedoch instabil. Zwillingssterne waren nicht unter den Lösungen, da der Übergangsdruck relativklein sein muss, während der Energiedichtesprung eher gross sein sollte. Das Auftreten zweier stabiler Äste in der Masse Radius Relation kann allerdingsmit dem SU(3) Modell und entsprechendem chiralen Phasenübergang modelliert werden. Für einen gewissen Parameterbereich einhergehend mit kleinem Wert des Vakuum Druckes B konnten Nicht-Linearitäten in der Zustangsgleichungzur Lösung der TOV Gleichung beitragen. Im Weitern ist das Zusammenspiel der Vektorkopplung und der Sigma Mesonen Masse einflussreich auf die Lösungen, welche auf Kausalität, Stabilität und neben der 2 Sonnenmassen Bedingung noch auf Restriktionen vom millisecond pulsar PSR J1748-2446ad untersucht wurden.Mit Weltraummissionen wie etwa NICER (Neutron star Interior CompositionExploreR) sollte die Radiusbestimmung kompakter Objekte in Zukunft bis auf einen Kilometer genau bestimmt werden können. Die Entdeckung von zweiSternen mit der gleichen Masse und unterschiedlichen Radien wäre in der Tat ein Beweis für die Existenz von Zwillingssternen, welche dann die Theorie des Phasenüberganges in dichter Materie untermauern würde. Das Kollaps-Szenario eines Zwillingssternes würde weiteren Aufschluss über Neutrino-Emmissivität, Gamma-ray burster und Gravitationswellen Signale geben können. Dynamische Simulationen in allgemein relativistischem Kontext für compact star merger mit den hier diskutierten Zustandsgleichungen sind bereits in Planung, um Eigenschaftenwie beispielsweise das Temperatur- und Dichteprofil solcher Objekte genauer zu analysieren.
In the field of strongly correlated electron systems, there is a long standing discussion on whether lattice degrees of freedom play a role for several physical phenomena, among them the Mott MI transition and charge-ordering transition. Charge-transfer salts of the ..-(BEDT-TTF)2X and (TMTCF)2X families have been revealed as model systemss for the study of the latter phenomena. The (TMTCF)2X salts have been recognized as model systems for studying correlation effects in 1D, while the (BEDT-TTF)-based materials for such studies in 2D. In this work, high-resolution dilatometry experiments were performed in order to address these issues. The main results obtained are summarized below. ...
Thermal expansion measurements provide a sensitive tool for exploring a material's thermodynamic
properties in condensed matter physics as they provide useful information
on the electronic, magnetic and lattice properties of a material. In this thesis, thermal
expansion measurements have been carried out both at ambient-pressure and under hydrostatic
pressure conditions. From the materials point of view, the spin-liquid candidate
Kappa-(BEDT-TTF) 2 Cu 2(CN)3 has been studied extensively as a function of temperature and
magnetic field. Azurite, Cu 3 (CO 3) 2 (OH) 2 - a realization of a one-dimensional distorted
Heisenberg chain is also studied both at ambient and hydrostatic pressure to demonstrate
the proper functioning of the newly built setup "thermal expansion under pressure". ...
We derive the thermal noise spectrum of the longitudinal and transverse electric field operator of a given wave vector starting from the quantum-statistical definitions and relate it to the frequency and wave vector dependent complex conductivity in a homogeneous, isotropic system of electromagnetic interacting charged particles in the frame of the non-relativistic QED. No additional assumptions except the validity of linear response are used in the proof. The Nyquist formula for vanishing frequency, as well as the noise spectral density of Callen-Welton follow as byproduct. Furthermore we discuss also the noise of the photon occupation numbers.
In this proceeding the emergence of a composite, adjoint-scalar field as an average over (trivial holonomy) calorons and anti-calorons is reviewed. This composite field acts as a background field to the dynamics of perturbative gluons, to which it is coupled via an effective, gauge invariant Lagrangian valid for temperatures above the deconfinement phase transition. Moreover a Higgs mechanism is induced by the composite field: two gluons acquire a quasi-particle thermal mass. On the phenomenological side the composite field acts as a bag pressure which shows a linear dependence on the temperature. As a result the linear rise with temperature of the trace anomaly is obtained and is compared to recent lattice studies.
It has been demonstrated that Statistical Hadronization Model fits perfectly to particle yields at freeze-out in heavy-ion and hadron collisions at LHC, RHIC and SPS, where quark-gluon plasma is created. It is however entirely not clear if particles emitted in the few-GeV energy regime can be understood as emerging from thermalized hadronic medium. Our recent work suggests that this might be the case. By implementing appropriate fireball geometry and expansion pattern in the THERMINATOR (THERMal heavy IoN generATOR) it was possible to describe not only yields, but also the spectra of most abundant particles measured at GSI SIS18. Most of the latter are pure prediction of the model. We present details of the model and extended comparison with experimental data and discuss further developments.
The rapidity distribution of thermal photons produced in Pb+Pb collisions at CERN-SPS energies is calculated within scaling and three- fluid hydrodynamics. It is shown that these scenarios lead to very different rapidity spectra. A measurement of the rapidity dependence of photon radiation can give cleaner insight into the reaction dynamics than pion spectra, especially into the rapidity dependence of the temperature.
Off-central heavy-ion collisions are known to feature magnetic fields with magnitudes and characteristic gradients corresponding to the scale of the strong interactions. In this work, we employ equilibrium lattice simulations of the underlying theory, QCD, involving similar inhomogeneous magnetic field profiles to achieve a better understanding of this system. We simulate three flavors of dynamical staggered quarks with physical masses at a range of magnetic fields and temperatures, and extrapolate the results to the continuum limit. Analyzing the impact of the field on the quark condensate and the Polyakov loop, we find non-trivial spatial features that render the QCD medium qualitatively different as in the homogeneous setup, especially at temperatures around the transition. In addition, we construct leading-order chiral perturbation theory for the inhomogeneous background and compare its prediction to our lattice results at low temperature. Our findings will be useful to benchmark effective theories and low-energy models of QCD for a better description of peripheral heavy-ion collisions.
Off-central heavy-ion collisions are known to feature magnetic fields with magnitudes and characteristic gradients corresponding to the scale of the strong interactions. In this work, we employ equilibrium lattice simulations of the underlying theory, QCD, involving similar inhomogeneous magnetic field profiles to achieve a better understanding of this system. We simulate three flavors of dynamical staggered quarks with physical masses at a range of magnetic fields and temperatures, and extrapolate the results to the continuum limit. Analyzing the impact of the field on the quark condensate and the Polyakov loop, we find non-trivial spatial features that render the QCD medium qualitatively different as in the homogeneous setup, especially at temperatures around the transition. In addition, we construct leading-order chiral perturbation theory for the inhomogeneous background and compare its prediction to our lattice results at low temperature. Our findings will be useful to benchmark effective theories and low-energy models of QCD for a better description of peripheral heavy-ion collisions.
Off-central heavy-ion collisions are known to feature magnetic fields with magnitudes and characteristic gradients corresponding to the scale of the strong interactions. In this work, we employ equilibrium lattice simulations of the underlying theory, QCD, involving similar inhomogeneous magnetic field profiles to achieve a better understanding of this system. We simulate three flavors of dynamical staggered quarks with physical masses at a range of magnetic fields and temperatures, and extrapolate the results to the continuum limit. Analyzing the impact of the field on the quark condensate and the Polyakov loop, we find non-trivial spatial features that render the QCD medium qualitatively different as in the homogeneous setup, especially at temperatures around the transition. In addition, we construct leading-order chiral perturbation theory for the inhomogeneous background and compare its prediction to our lattice results at low temperature. Our findings will be useful to benchmark effective theories and low-energy models of QCD for a better description of peripheral heavy-ion collisions.
Off-central heavy-ion collisions are known to feature magnetic fields with magnitudes and characteristic gradients corresponding to the scale of the strong interactions. In this work, we employ equilibrium lattice simulations of the underlying theory, QCD, involving similar inhomogeneous magnetic field profiles to achieve a better understanding of this system. We simulate three flavors of dynamical staggered quarks with physical masses at a range of magnetic fields and temperatures, and extrapolate the results to the continuum limit. Analyzing the impact of the field on the quark condensate and the Polyakov loop, we find non-trivial spatial features that render the QCD medium qualitatively different as in the homogeneous setup, especially at temperatures around the transition. In addition, we construct leading-order chiral perturbation theory for the inhomogeneous background and compare its prediction to our lattice results at low temperature. Our findings will be useful to benchmark effective theories and low-energy models of QCD for a better description of peripheral heavy-ion collisions.
Electromagnetic probes such as photons and dielectrons (e+e− pairs) are a unique tool to study the space-time evolution of the hot and dense matter created in ultrarelativistic heavy-ion collisions. At low dielectron invariant mass (mee), thermal radiation from the hot hadronic phase contributes to the dielectron spectrum via decays of ρ mesons, whose spectral function is sensitive to chiral-symmetry restoration. At larger mee, thermal radiation from the quark–gluon plasma carries information about the early temperature of the medium. At LHC energies, it is nevertheless dominated by a large background from correlated heavy-flavor hadron decays affected by energy loss and flow in the medium. Complementary to the real photon measurements, dielectron data also allow the extraction of the real direct photon fraction, including thermal photons at low pair transverse momentum pT,ee. The latest ALICE results on dielectron studies in Pb-Pb, and in inelastic and high-multiplicity pp collisions, at √sNN = 5.02 TeV and at √s = 13 TeV, respectively, are presented and compared to simulations and expectations from theory. The status of the Run 3 analysis is also reported.
In der vorliegenden Arbeit wird versucht, die sog. selektiven Effekte der Ultrakurzwellentherapie (UKWT) thermisch zu erklären, und zwar durch die Temperaturschwingungen, welche durch die pulsierende Wärmebildung der Hochfrequenz(HF)-Bestrahlung in Mikroorganismen hervorgerufen werden. Bei Annahme verschiedener Mechanismen der Energieumsetzung in Wärme innerhalb oder an der Oberfläche von Teilchen, die sich in einem Suspensionsmedium befinden, wird eine Art thermische Resonanz (Selektivität) aufgefunden. Die Lage der Selektivität, abhängig von der Frequenz des HF-Feldes, der Teilchengröße und der Wärmeleitfähigkeit des Teilcheninneren und das Verhältnis der Temperaturamplitude des Teilchenmittelpunkts zur Umgebungstemperatur lassen die Vermutung zu, in Übereinstimmung mit experimentellen Befunden bei der UKWT, daß der Effekt zur Erklärung der Wirksamkeit dieser medizinischen Behandlungsmethode beiträgt. Zurückgreifend auf ältere Arbeiten wird der Anlaufvorgang des Temperaturfeldes in Mikroorganismen, der durch das Einschalten des HF-Feldes entsteht, untersucht, durch einen Modellversuch gestützt und seine Bedeutung für die UKWT, die vielfach angenommen wurde, der Kürze der Anlaufzeiten wegen in Frage gestellt.
Diese Arbeit beschäftigt sich mit der Wasserkühlung einer normalleitenden CH-Kavität. Insbesondere stellt sich die Frage, ob die im CST Thermal Steady State Solver simulierten Temperaturen mit Messungen während High Power Tests übereinstimmen. Zusätzlich interessiert, inwiefern die Temperatur über die dissipierte Leistung aus dem CST Eigenmode Solver und dem gemessenen Volumenstrom im Kanal abgeschätzt werden kann. In dem Kontext wird auch geklärt, ob die Reihenschaltung der Mantelkanäle den Kühlanforderungen genügt.
Neben Volumenstrom- und Druckmessungen an den in Reihe und parallelgeschalteten Kanälen werden die Leistungs- und Temperaturwerte der Konditionierung in sämtlichen Simulationen aufgegriffen. Indem die Kavität in einzelne Sektionen unterteilt wird und in diesen die dissipierte Leistung mit dem Eigenmode Solver simuliert wird, die ein Kühlkanal abführt, werden die Temperaturerhöhungen direkt berechnet und verglichen.
Zusammengefasst hat sich der Durchfluss in kritischen Bauteilen wie den Stützen durch die Reihenschaltung der Mantelkanäle erhöht und wird damit empfohlen. Es werden die simulierten Temperaturverteilungen gezeigt. Die Näherung über den Eigenmode Solver liefert erneut für die thermisch belasteten Bauteile wie die Stützen präzise Vorhersagen.
Abschließend werden Erfahrungen aus dem Institut in dieser Arbeit zusammengetragen und die Verwendung des Steady State Solver freigegeben.
We develop a framework to relate proton number cumulants measured in heavy-ion collisions within a momentum space acceptance to the susceptibilities of baryon number, assuming that particles are emitted from a fireball with uniform distribution of temperature and baryochemical potential, superimposed on a hydrodynamic flow velocity profile. The rapidity acceptance dependence of proton cumulants measured by the HADES Collaboration in √sNN = 2.4 GeV Au-Au appears to be consistent with thermal emission of nucleons from a grand-canonical heat bath, with the extracted baryon number susceptibilities exhibiting an hierarchy χB 4 >> −χB 3 >> χB 2 >> χB 1 . Naively, this could indicate large nonGaussian fluctuations that might point to the presence of the QCD critical point close to the chemical freeze-out at T ∼ 70 MeV and μB ∼ 850 − 900 MeV. However, the description of the experimental data at large rapidity acceptances becomes challenging once the effect of exact baryon number conservation is incorporated, suggesting that more theoretical and experimental studies are needed to reach a firm conclusion.
This thesis aimed at identifying and understanding the interplay of charge and lattice degrees of freedom at metal-insulator transitions that are driven by strong electron correlations, i.e., Mott and charge-order metal-insulator transitions. To this end, measurements of the thermal expansion were performed, which have proven to be particularly suited to deliver insight into the role of lattice degrees of freedom in strongly correlated electron systems. Prime examples of such systems are the herein studied organic charge-transfer salts which stand out by a high tunability of the interaction strength.
The central topic of this thesis was the investigation of the universal behavior of the pressure-induced finite-temperature Mott critical endpoint in the organic charge-transfer salt kappa-(BEDT-TTF)2Cu[N(CN)2]Cl. In the present work, it was proven experimentally that lattice effects play a crucial role for the universal behavior, in contrast to the assumption made in previous works.
We investigate the phase structure of strongly interacting matter at non-vanishing isospin before the onset of pion condensation in the framework of the unquenched Polyakov–Quark-Meson model with 2+1 quark flavors. We show results for the order parameters and all relevant thermodynamic quantities. In particular, we obtain a moderate change of the pressure with isospin at vanishing baryon chemical potential, whereas the chiral condensate decreases more appreciably. We compare the effective model to recent lattice data for the decrease of the pseudo-critical temperature with the isospin chemical potential. We also demonstrate the major role played by the value of the pion mass in the curvature of the transition line, and the need for lattice results with a physical pion mass. Limitations of the model at nonzero chemical potential are also discussed.
Hadron lists based on experimental studies summarized by the Particle Data Group (PDG) are a crucial input for the equation of state and thermal models used in the study of strongly-interacting matter produced in heavy-ion collisions. Modeling of these strongly-interacting systems is carried out via hydrodynamical simulations, which are followed by hadronic transport codes that also require a hadronic list as input. To remain consistent throughout the different stages of modeling of a heavy-ion collision, the same hadron list with its corresponding decays must be used at each step. It has been shown that even the most uncertain states listed in the PDG from 2016 are required to reproduce partial pressures and susceptibilities from Lattice Quantum Chromodynamics with the hadronic list known as the PDG2016+. Here, we update the hadronic list for use in heavy-ion collision modeling by including the latest experimental information for all states listed in the Particle Data Booklet in 2021. We then compare our new list, called PDG2021+, to Lattice Quantum Chromodynamics results and find that it achieves even better agreement with the first principles calculations than the PDG2016+ list. Furthermore, we develop a novel scheme based on intermediate decay channels that allows for only binary decays, such that PDG2021+ will be compatible with the hadronic transport framework SMASH. Finally, we use these results to make comparisons to experimental data and discuss the impact on particle yields and spectra.