Hanbury-Brown-Twiss interferometry within the UrQMD transport approach

In this thesis, Hanbury-Brown-Twiss (HBT) interferometry is used together with the Ultrarelativistic Quantum Molecular Dynamics (UrQMD) to analyse the time and space structure of heavy-ion collisions. The first chapter after the introduction gives an overview of the different types of models used in the field of heavy-ion collisions and a introduction of the UrQMD model in more detail. The next chapter explains the basics of Hanbury-Brown-Twiss correlations, including azimuthally sensitive HBT (asHBT). Results section: 4. Charged Multiplicities from UrQMD 5. Formation time via HBT from pp collisions at LHC 6. HBT analysis of Pb+Pb collisions at LHC energies 7. HBT scaling with particle multiplicity 8. Compressibility from event-by-event HBT 9. Tilt in non-central collisions 10. Shape analysis of strongly-interacting systems 11. Measuring a twisted emission geometry This thesis covers the standard integrated HBT analyses, extracting the Pratt-Bertsch radii, at LHC energies. The analyses at these energies showed a too soft expansion in UrQMD probably related to the absence of a partonic phase in UrQMD. The most promising results in this thesis at these energies are the restriction of the formation time to a value smaller than 0.8 fm/c and furthermore, the results from the asHBT analyses. In simulations of non-central heavy-ion collisions at energies of Elab= 6, 8 and 30 AGeV the validity of the formulae to calculate the tilt angle via asHBT has been checked numerically, even for the case of non-Gaussian, flowing sources. On this basis has been developed and test in the course of this thesis that allows to measure a scale dependent tilt angle experimentally. The signal should be strongest at FAIR energies.In dieser Arbeit wird Hanbury-Brown-Twiss (HBT) Interferometrie benutzt um im Rahmen des Models „Ultrarelativistische Quanten Molekular Dynamik“ (UrQMD) die Raum und Zeit Geometrie von Schwerionen Kollisionen zu untersuchen. Das erste Kapitel nach der Einleitung gibt einen Überblicke über die verschiedenen Sorten von Modellen, die im Feld zur Beschreibung von Schwerionen Kollisionen genutzt werden. Dabei wird ein besonderer Fokus auf die Beschreibung des UrQMD Modelles gesetzt da dieses für die Untersuchungen in dieser Arbeit verwendet wurde. Das nächste Kapitel gibt eine Einführung in die Grundlagen der HBT Korrelationen und enthält auch einen Abschnitt über azimuthal sensitives HBT (asHBT), welches für diese Arbeit wichtig ist. Resultat Kapitel: 4. Charged Multiplicities from UrQMD 5. Formation time via HBT from pp collisions at LHC 6. HBT analysis of Pb+Pb collisions at LHC energies 7. HBT scaling with particle multiplicity 8. Compressibility from event-by-event HBT 9. Tilt in non-central collisions 10. Shape analysis of strongly-interacting systems 11. Measuring a twisted emission geometry Die Resultat Kapitel enthalten die Standard Analysen zu den HBT bei LHC Energien. Dabei zeigt sich, dass die Expansion des Mediums in UrQMD zu weich ist. Dies hängt wahrscheinlich damit zusammen, dass in UrQMD keine partonische Wechselwirkungsphase vorhanden ist. Die interessantesten Ergebnisse sind zum einen die Beschränkung der Formationszeit auf einen Wert kleiner als 0.8 fm/c und zum anderen die Resultate der asHBT Analysen. In der Simulation von semizentralen Kollisionen bei Energien von Elab= 6, 8 und 30 AGeV wurde die Anwendbarkeit der Formel zur Berechnung des Drehungswinkels im Falle von nicht-Gaußschen Quellen mit Fluss numerisch nachgewiesen. Auf dieser Grundlage haben wir ein Verfahren entwickelt und getestet, das es erlaubt einen skalenabhängigen Drehungswinkel experimentell zu messen. Das Signal für diesen Drehungswinkel sollte bei FAIR Energien am größten sein

Multi-particle interactions within the UrQMD approach

A mechanism for locally density-dependent dynamic parton rearrangement and fusion has been implemented into the Ultrarelativistic Quantum Molecular Dynamics (UrQMD) approach. The same mechanism has been previously built in the Quark Gluon String Model (QGSM). This rearrangement and fusion approach based on parton coalescence ideas enables the description of multi-particle interactions, namely 3 -> 3 and 3 -> 2, between (pre)hadronic states in addition to standard binary interactions. The UrQMD model (v2.3) extended by these additional processes allows to investigate implications of multi-particle interactions on the reaction dynamics of ultrarelativistic heavy ion collisions. The mechanism, its implementation and first results of this investigation are presented and discussed

Implications on the collision dynamics via azimuthal sensitive HBT from UrQMD : the Seventh Workshop on Particle Correlations and Femtoscopy, September 20 - 24 2011, University of Tokyo, Japan

We explore the shape and orientation of the freezeout region of non-central heavy ion collisions. For this we fit the freezeout distribution with a tilted ellipsoid. The resulting tilt angle is compared to the same tilt angle extracted via an azimuthally sensitive HBT analysis. This allows to access the tilt angle experimentally, which is not possible directly from the freezeout distribution. We also show a systematic study on the system decoupling time dependence on dNch/dh, using HBT results from the UrQMD transport model. In this study we found that the decoupling time scales with (dNch/dh)1/3 within each energy, but the scaling is broken across energies

HBT radii from the UrQMD transport approach at different energies

We present results on Hanbury Brown-Twiss (HBT) radii extracted from the Ultra-relativistic Molecular Dynamics (UrQMD) approach to relativistic heavy ion collisions. The present investigation provides a comparison of results from pure hadronic transport calculations to a Boltzmann + Hydrodynamic hybrid approach with an intermediate hydrodynamic phase. For the hydrodynamic phase different Equations of State (EoS) have been employed, i.e. bag model, hadron resonance gas and a chiral EoS. The influence of various freeze-out scenarios has been investigated and shown to be negligible if hadronic rescatterings after the hydrodynamic evolution are included. Furthermore, first results of the source tilt from azimuthal sensitive HBT and the direct extraction from the transport model are presented and exhibit a very good agreement with E895 data at AGS

UrQMD calculations of two-pion HBT correlations in p+p and Pb+Pb collisions at LHC energies

Two-pion Hanbury-Brown-Twiss (HBT) correlations for p+p and central Pb+Pb collisions at the Large-Hadron-Collider (LHC) energies are investigated with the ultra-relativistic quantum molecular dynamics model combined with a correlation afterburner. The transverse momentum dependence of the Pratt-Bertsch HBT radii $R_{long}$, $R_{out}$, and $R_{side}$ is extracted from a three-dimensional Gaussian fit to the correlator in the longitudinal co-moving system. In the p+p case, the dependence of correlations on the charged particle multiplicity and formation time is explored and the data allows to constrain the formation time in the string fragmentation to $\tau_f \leq 0.8$ fm/c. In the Pb+Pb case, it is found that $R_{out}$ is overpredicted by nearly 50%. The LHC results are also compared to data from the STAR experiment at RHIC. For both energies we find that the calculated $R_{out}/R_{side}$ ratio is always larger than data, indicating that the emission in the model is less explosive than observed in the data.Comment: 9 pages, 4 figures, 1 table. Talk given by Qingfeng Li at the 11th International Conference on Nucleus-Nucleus Collisions (NN2012), San Antonio, Texas, USA, May 27-June 1, 2012. To appear in the NN2012 Proceedings in Journal of Physics: Conference Series (JPCS

Charged particle (pseudo-)rapidity distributions in proton+anti-proton/proton+proton and Pb+Pb/Au+Au collisions from SPS to LHC energies from UrQMD

We present results for final state charged particle (pseudo-)rapidity distributions in $\rm{p}$ + $\bar{\rm{p}}$ / $\rm{p}$ + $\rm{p}$ and Pb+Pb/Au+Au at ultra high energies (17.3 GeV $\leq$ $\sqrt{s_{\rm{NN}}}$ $\leq$ 14 TeV) from the Ultra-relativistic Quantum Molecular Dynamics (UrQMD-v2.3) model. In addition, excitation functions of produced charged particle multiplicities ($N_{\rm{ch}}$) and pseudorapidity spectra are investigated up to LHC energies. Good agreement is observed between UrQMD and measured pseudorapidity distributions of charged particles up to the highest Tevatron and Sp$\bar{\rm{p}}$S energies.Comment: 6 pages, 7 figure

Formation time dependence of femtoscopic ππ\pi \pi correlations in p+p collisions at sNN\sqrt{s_{NN}}=7 TeV

We investigate femtoscopic $\pi \pi$ correlations using the UrQMD approach combined with a correlation afterburner. The dependence of $\pi \pi$ correlations on the charged particle multiplicity and formation time in p+p collisions at $\sqrt{s_{NN}}$= 7 TeV is explored and compared to present ALICE data. The data allows to constrain the formation time in the string fragmentation to $\tau_f \leq 0.8$ fm/c.Comment: 9 pages, 2 figure