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In April and May 2012 data on Au+Au collisions at beam energies of Ekin = 1.23A GeV were recorded with the High Acceptance Di-Electron Spectrometer, which is located at the GSI Helmholtz Center for Heavy Ion Research in Darmstadt, Germany. At this beam energy all hadrons containing strangeness are produced below their elementary production threshold. The required energy is not available in binary NN collisions but must be provided by the system e.g. through multi-particle interactions or medium effects like a modified in-medium potential (e.g. KN/ΛN potential). Thus, a high sensitivity to these medium effects is expected in the investigated system.
The baryon-dominated systems created in relativistic heavy-ion collisions (HIC) at SIS18 energies reach densities of about 2-3 times ground state density p0 and may be similar to the properties of matter expected in the inner core of neutron stars. It is in particular the behavior of hadrons containing strangeness, i.e. kaons and hyperons, and their potentials in the dense medium which may have severe implications on astrophysical objects and processes. As ab-initio calculations of quantum chromodynamics (QCD) cannot be performed rigorously on the lattice at finite baryo-chemical potentials due to the fermion sign problem, effective descriptions have to be used in order to model properties of dense systems and the involved particles. The only way to access the in-medium potential of strange hadrons above nuclear ground state density p0 is by comparing data from relativistic HIC to such effective microscopic models. Up to now, not much data on neutral kaons and Λ hyperons are available from heavy collision systems close to their NN production threshold. These two electromagnetically uncharged strange hadrons are in particular well suited to study their potential in a dense nucleon-dominated environment as their kinematic spectra are not affected by Coulomb interactions.
Anisotropic collective flow of protons resulting from non-central heavy ion collisions is a unique hadronic observable providing information about the early stage of the nuclear collision. The analysis of collective flow in the energy regime between 1-2 AGeV enables the study of the phase diagram of hadronic matter at a high baryochemical potential µb, as well as the analysis of the equation of state at densities up to the threefold of the ground state density ρ0.
The algorithms of the standard event plane method and the scalar product method are used to analyse directed and elliptic flow of protons in a centrality range of 0-40 % most central events.
Prior to the analysis of experimental data, the respective influence of the reconstruction procedure on the algorithms is examined using Monte Carlo simulations based on the Ultra relativistic Quantum Molecular Dynamics (UrQMD) model.
Subsequently, experimental data measured in April 2012 with the High Acceptance DiElectron Spectrometer (HADES) is analysed using both methods. About 7.3 · 109 Au+Au events at a kinetic beam energy of 1.23 AGeV, equivalent to a centre of mass energy of √sNN = 2.42 GeV were recorded. A multi-differential analysis is feasible as the HADES detector provides a good transverse momentum and rapidity coverage.
Both algorithms result in identical values for directed and elliptic flow across all centrality classes within the observable phase space of protons. The calculated integrated value of v2 at mid rapidity is in good agreement with world data.
Electron identification with a likelihood method and measurements of di-electrons for the CBM-TRD
(2017)
In this work a likelihood method has been implemented and investigated as particle identification algorithm for the CBM-TRD.
The creation of the probability distributions for the likelihood method via V0-topologies seems to be feasible and the purity of the obtained samples is sufficient for the usage in the likelihood method.
The comparison between the ANN and the likelihood method shows no differences in the identification performance. The pion suppression factor reaches the same values for the same electron identification efficiencies and the yields of the resulting di-lepton signals are comparable. The signal-to-background ratios for both methods have the same values and show a value of about 10−2 in the invariant mass range of minv = 1.5 - 2.5 GeV/c2, which is expected to be sufficient to provide access to the thermal in-medium and QGP radiation.
The investigation of a detector system without a TRD shows no pion suppression for a momentum above p = 6 GeV/c. Therefore, the background contributions increase drastically and the signal-to-background ratio decreases at all invariant masses, but especially in the invariant mass range of minv = 1.5 - 2.5 GeV/c2.
The background contributions in the invariant mass range of minv = 1.5 - 2.5 GeV/c 2 are also influenced by the selected electron identification efficiency of the TRD, which significantly shifts the fraction of the eπ contributions relative to the total number of pairs.
In April and May 2012 data on Au+Au collisions at beam energies of Ekin = 1.23A GeV were collected with the High Acceptance Di-Electron Spectrometer (HADES) at the GSI Helmholtzzentrum für Schwerionenforschung facility in Darmstadt, Germany. In this thesis, the production of deuterons in this collision system is investigated.
A total number of 2.1 × 109 Au+Au events is selected, containing the most central 0-40% of events. After particle identification, based on a mass determination via time-of-flight and momentum and on a measurement of the energy loss, the transverse mass spectra of the deuteron candidates are extracted for various rapidities and subsequently corrected for acceptance and efficiency.
The inverse slope parameter of a Boltzmann fit applied to the transverse mass spectra at midrapidity, which is referred to as the effective temperature, is extracted. For a static thermal source, this parameter corresponds to the kinetic freeze-out temperature Tkin and is therefore expected to be smaller or equal to the chemical freeze-out temperature Tchem. The extracted effective temperature of Tef f = (190 ± 10) MeV however exceeds the chemical freeze-out temperature that was obtained by a statistical model fit to different particle yields. The effective temperatures of various particle species, obtained in previous analyses, suggest a systematic rise with increasing particle mass, which is confirmed by the deuteron results.
An explanation can be the influence of a collective expansion with a radial expansion velocity βr. By fitting a Siemens-Rasmussen function to the transverse mass spectra, the global temperature of T = (100 ± 8) MeV and radial expansion velocity βr = 0.37 ± 0.01 are obtained. This temperature is still very high and only takes into account the production of deuteron nuclei.
The simultaneous fit of a blast-wave function to the transverse mass spectra of deuterons and other particles, as obtained by previous analyses, considers a velocity profile for the radial expansion velocity and takes into account the production of various particle species. The resulting global temperature Tkin = (68 ± 1) MeV and average transverse expansion velocity hβri = 0.341 ± 0.003 are within the expected range for the collision energy.
The Siemens-Rasmussen fits are also used to extrapolate the transverse mass spectra into unmeasured regions, to integrate them and obtain a rapidity-dependent count rate. This count rate exhibits a thermal shape for central events and shows increasing spectator contributions for more peripheral events.
The invariant yield spectra of the deuterons are compared to those of protons, as obtained by a previous analysis, in the context of a nucleon coalescence model. The hereby extracted nucleon coalescence factor B2 = (4.6 ± 0.1) × 10−3 agrees with the expected result for the beam energy that was studied.
Das CBM Experiment konzentriert sich auf die Untersuchung des Phasendiagramms von stark wechselwirkender Materie im Bereich moderater Temperaturen, aber hoher Netto-Baryonendichte. Dabei sollen unter anderem Proben aus dem frühen und hochdichten Stadium des Quark-Gluon Plasmas detektiert werden. Ein Beispiel dafür ist das J/ψ-Meson. Das Vektormeson gilt wegen seiner Eigenschaften und Interaktion mit dem QGP als eine der wichtigen Proben stark wechselwirkender Materie.
In dieser Arbeit wird die Performance der Detektoren anhand einer Simulation in Hinsicht auf die Messung des J/ψ-Mesons studiert. Es werden hierfür unterschiedliche Simulationsansätze verglichen. Die Simulation wird im FairRoot und CbmRoot Framework durchgeführt. Es werden Proton+Gold Kollisionen bei einer Strahlenergie von 30 GeV pro Proton simuliert. Dabei verwenden wir das Standard-Setup des SIS100 für Elektronen. Das J/ψ-Meson wird über den e+e−-Zerfallskanal rekonstruiert. Bei der J/ψ-Rekonstruktion werden zuerst Schnitte gesetzt, mit der ein großer Teil der Teilchenspuren, die nicht aus J/ψ-Zerfällen stammen, aussortiert werden und so der Untergrund verringert wird.
Die Effizienz für Elektronen im Detektor-Setup RICH+TRD+TOF beträgt 65 Prozent. Für das J/ψ-Meson erhalten wir mit den gleichen Detektoren eine Effizienz von 25 Prozent. Das invariante Massenspektrum, das wir aus einer Simulation mit 8,5 Millionen Ereignisse bilden, zeigt uns, dass der hauptsächliche Anteil des Untergrunds aus Pion-Elektron-Kombinationen besteht. Es folgen im e+e−-Zerfallskanal unkorrelierte Elektron-Positron-Kombinationen als der zweitgrößte Beitrag zum Untergrund. Die Statistik ist bei der Full Simulation zu gering, um das J/ψ-Signal extrahieren zu können. Eine Integration liefert uns ein J/ψ Signal von 0,021 bei 8,5 Millionen Ereignisse, d.h. für die Detektion eines J/ψ-Mesons werden ca. 1010 Ereignisse benötigt.
Die Fast Simulation Methode ermöglicht uns in kürzerer Zeit eine größere Menge an Ereignissen zu simulieren. Dazu werden Information aus der Full Simulation entnommen, die als Antwort-Funktionen bezeichnet werden. Die Antwort-Funktionen werden der Fast Simulation übergeben, um so zeitintensive Prozesse in der Simulation überspringen zu können. Zum Zeitpunkt der Arbeit fehlen Pionen, Protonen und Kaonen in den invarianten Massenspektren der Fast Simulation. Das Problem soll in Zukunft behoben werden. Folglich haben wir ein invariantes Massenspektrum mit 85 Millionen simulierten Ereignissen, jedoch ohne Pionen, Protonen und Kaonen. Wir erhalten daher ein signifikantes J/ψ-Signal, allerdings mit einem unrealistisch hohen S/B-Verhältnis. Ein weiteres Ziel, nach der Implementierung der fehlenden Teilchen, soll die nochmalige Extrahierung des J/ψ-Signals mit korrektem Untergrund sein.