Latest documents http://publikationen.stub.uni-frankfurt.de/index/index/ Mon, 17 Dec 2012 16:15:29 +0100 Mon, 17 Dec 2012 16:15:29 +0100 http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/27291 Direct photon emission in heavy-ion collisions is calculated within a relativistic micro+macro hybrid model and compared to the microscopic transport model UrQMD. In the hybrid approach, the high-density part of the collision is calculated by an ideal 3+1-dimensional hydrodynamic calculation, while the early (pre-equilibrium-) and late (rescattering-) phase are calculated with the transport model. Different scenarios of the transition from the macroscopic description to the transport model description and their effects are studied. The calculations are compared to measurements by the WA98-collaboration and predictions for the future CBM-experiment are made. Björn Bäuchle; Marcus Bleicher conferenceobject http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/27291 Mon, 17 Dec 2012 16:15:29 +0100 http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/27290 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. Gunnar Gräf; Elliot Mount; Michael Annan Lisa; Marcus Bleicher conferenceobject http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/27290 Mon, 17 Dec 2012 16:10:14 +0100 http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/27776 The biological effects of energetic heavy ions are attracting increasing interest for their applications in cancer therapy and protection against space radiation. The cascade of events leading to cell death or late effects starts from stochastic energy deposition on the nanometer scale and the corresponding lesions in biological molecules, primarily DNA. We have developed experimental techniques to visualize DNA nanolesions induced by heavy ions. Nanolesions appear in cells as “streaks” which can be visualized by using different DNA repair markers. We have studied the kinetics of repair of these “streaks” also with respect to the chromatin conformation. Initial steps in the modeling of the energy deposition patterns at the micrometer and nanometer scale were made with MCHIT and TRAX models, respectively. Marcus Bleicher; Lucas Burigo; Marco Durante; Maren Herrlitz; Michael Krämer; Igor Mishustin; Iris Müller; Francesco Natale; Igor Pshenichnov; Stefan Schramm; Gisela Taucher-Scholz; Cathrin Wälzlein article http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/27776 Thu, 13 Dec 2012 16:28:23 +0100 http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/17194 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. Gunnar Gräf; Elliott Mount; Hannah Petersen; Qingfeng Li; Mike Lisa; Marcus Bleicher article http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/17194 Fri, 29 Apr 2011 16:15:15 +0200 http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/17193 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. Gerhard Burau; Gunnar Gräf; Hannah Petersen; Marcus Bleicher article http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/17193 Fri, 29 Apr 2011 16:10:15 +0200 http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/16727 We present the current status of hybrid approaches to describe heavy ion collisions and their future challenges and perspectives. First we present a hybrid model combining a Boltzmann transport model of hadronic degrees of freedom in the initial and final state with an optional hydrodynamic evolution during the dense and hot phase. Second, we present a recent extension of the hydrodynamical model to include fluctuations near the phase transition by coupling a chiral field to the hydrodynamic evolution. Marlene Nahrgang; Christoph Herold; Stefan Schramm; Marcus Bleicher article http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/16727 Fri, 29 Apr 2011 15:51:23 +0200 http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/20408 Relying on the existing estimates for the production cross sections of mini black holes in models with large extra dimensions, we review strategies for identifying those objects at collider experiments. We further consider a possible stable final state of such black holes and discuss their characteristic signatures. Keywords: Black holes Horst Stöcker; Ben Koch; Marcus Bleicher article http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/20408 Thu, 02 Dec 2010 10:04:46 +0100 http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/20406 We study various fluctuation and correlation signals of the deconfined state using a dynamical recombination approach (quark Molecular Dynamics, qMD). We analyse charge ratio fluctuations, charge transfer fluctuations and baryon-strangeness correlations as a function of the center of mass energy with a set of central Pb+Pb/Au+Au events from AGS energies on (Elab = 4 AGeV) up to the highest RHIC energy available (V sNN = 200 GeV) and as a function of time with a set of central Au+Au qMD events at V sNN = 200 GeV with and without applying our hadronization procedure. For all studied quantities, the results start from values compatible with a weakly coupled QGP in the early stage and end with values compatible with the hadronic result in the final state. We show that the loss of the signal occurs at the same time as hadronization and trace it back to the dynamical recombination process implemented in our model. Stéphane Haussler; Marcus Bleicher; Stefan Scherer article http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/20406 Thu, 02 Dec 2010 09:27:47 +0100 http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/7408 Bei Darmstadt entsteht FAIR, eines der größten internationalen Forschungszentren für Physik. Durch das von der Landesregierung geförderte Exzellenzzentrum »HIC for FAIR« erhält die Forschung in Hessen die einmalige Chance, sich direkt an globaler Spitzenforschung zu beteiligen: auf der Suche nach den letzten Geheimnissen der Materie. Ingo Fröhlich; Marcus Bleicher; Gabriela Meyer article http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/7408 Mon, 18 Jan 2010 09:05:40 +0100 http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/7152 There is little doubt that Quantumchromodynamics (QCD) is the theory which describes strong interaction physics. Lattice gauge simulations of QCD predict that in the m,T plane there is a line where a transition from confined hadronic matter to deconfined quarks takes place. The transition is either a cross over (at low m) or of first order (at high m). It is the goal of the present and future heavy ion experiment at RHIC and FAIR to study this phase transition at different locations in the m,T plane and to explore the properties of the deconfined phase. It is the purpose of this contribution to discuss some of the observables which are considered as useful for this purpose. Jörg Aichelin; Hannah Petersen; Sascha Vogel; Marcus Bleicher article http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/7152 Thu, 08 Oct 2009 15:08:25 +0200 http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/6516 Rezension zu: Peter Woit : Not Even Wrong: The Failure of String Theory and the Continuing Challenge to Unify the Laws of Physics. Verlag Vintage, London 2006, 290 Seiten, 27,89 Euro. Marcus Bleicher review http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/6516 Tue, 12 May 2009 08:38:20 +0200 http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/927 Schwarze Löcher – das sind im Allgemeinen alles verschlingende, gigantisch schwere astronomische Objekte mit bis zu einigen Milliarden Sonnenmassen. Am Frankfurt Institute for Advanced Studies (FIAS) und am Institut für Theoretische Physik sind in den vergangenen fünf Jahren eine ganz neue Art von Schwarzen Löchern theoretisch vorhergesagt worden, die genau das Gegenteil der astronomisch gemessenen Giganten darstellen, nämlich winzig kleine Schwarze Löcher, so genannte »mini black holes«. Auftreten könnten sie, wenn im kommenden Jahr der neue Teilchenbeschleuniger am CERN in Genf in Betrieb genommen wird. Marcus Bleicher; Horst Stöcker article http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/927 Mon, 18 Jun 2007 09:07:52 +0200 http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/948 The effects of the onset of deconfinement on longitudinal and transverse flow are studied. First, we analyze longitudinal pion spectra from Elab = 2A GeV to √sNN = 200 GeV within Landau’s hydrodynamical model and the UrQMD transport approach. From the measured data on the widths of the pion rapidity spectra, we extract the sound velocity c2s in the early stage of the reactions. It is found that the sound velocity has a local minimum (indicating a softest point in the equation of state, EoS) at Ebeam = 30A GeV. This softening of the EoS is compatible with the assumption of the formation of a mixed phase at the onset of deconfinement. Furthermore, the energy excitation function of elliptic flow (v2) from Ebeam = 90A MeV to √sNN = 200 GeV is explored within the UrQMD framework and discussed in the context of the available data. The transverse flow should also be sensitive to changes in the equation of state. Therefore, the underestimation of elliptic flow by the UrQMD model calculation above Elab = 30A GeV might also be explained by assuming a phase transition from a hadron gas to the quark gluon plasma around this energy. This would be consistent with the model calculations, indicating a transition from hadronic matter to “string matter” in this energy range. Hannah Petersen; Marcus Bleicher article http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/948 Thu, 14 Jun 2007 13:17:03 +0200 http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/1689 Based on the UrQMD transport model, the transverse momentum and the rapidity dependence of the Hanbury-Brown-Twiss (HBT) radii R_L, R_O, R_S as well as the cross term R_OL at SPS energies are investigated and compared with the experimental NA49 and CERES data. The rapidity dependence of the R_L, R_O, R_S is weak while the R_OL is significantly increased at large rapidities and small transverse momenta. The HBT "life-time" issue (the phenomenon that the calculated sqrt R_O^2-R_S^2 value is larger than the correspondingly extracted experimental data) is also present at SPS energies. Qingfeng Li; Marcus Bleicher; Xianglei Zhu; Horst Stöcker preprint http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/1689 Fri, 16 Feb 2007 14:41:50 +0100 http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/2173 We examine experimental signatures of TeV-mass black hole formation in heavy ion collisions at the LHC. We find that the black hole production results in a complete disappearance of all very high p_T (> 500 GeV) back-to-back correlated di-jets of total mass M > M_f ~ 1 TeV. We show that the subsequent Hawking-decay produces multiple hard mono-jets and discuss their detection. We study the possibility of cold black hole remnant (BHR) formation of mass ~ M_f and the experimental distinguishability of scenarios with BHRs and those with complete black hole decay. Finally we point out that a Heckler-Kapusta-Hawking plasma may form from the emitted mono-jets. In this context we present new simulation data of Mach shocks and of the evolution of initial conditions until the freeze-out. Barbara Betz; Marcus Bleicher; Ulrich Harbach; Thomas J. Humanic; Benjamin Koch; Horst Stöcker preprint http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/2173 Tue, 31 Oct 2006 10:01:29 +0100 http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/2172 We propose to measure azimuthal correlations of heavy-flavor hadrons to address the status of thermalization at the partonic stage of light quarks and gluons in high-energy nuclear collisions. In particular, we show that hadronic interactions at the late stage cannot significantly disturb the initial back-to-back azimuthal correlations of DDbar pairs. Thus, a decrease or the complete absence of these initial correlations does indicate frequent interactions of heavy-flavor quarks and also light partons in the partonic stage, which are essential for the early thermalization of light partons. Kai Oliver Schweda; Xianglei Zhu; Marcus Bleicher; Shengli Huang; Horst Stöcker; Nu Xu; Pengfei Zhuang preprint http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/2172 Tue, 31 Oct 2006 09:40:57 +0100 http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/3418 We study forward-backward charge fluctuations to probe the correlations among produced particles in ultra relativistic heavy ion collisions. We develop a model that describes the forward-backward dynamical fluctuations and apply it to interpret the recent PHOBOS data. Within the present model, the dynamical fluctuations are related to the particle production mechanism via cluster decay and to long range correlations between the forward and backward rapidity hemispheres. We argue that with a tight centrality cut, PHOBOS may see a strong decrease of the dynamical fluctuations. Within the present model, this deterioration of the correlation among the produced hadrons can be interpreted as a sign for the production of a hot, dense and interacting medium. Mohamed Abdel-Aziz; Marcus Bleicher preprint http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/3418 Wed, 14 Jun 2006 12:50:26 +0200 http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/2743 We demonstrate the occurrence of canonical suppression associated with the conservation of an U(1)-charge in current transport models. For this study a pion gas is simulated within two different transport approaches by incorporating inelastic and volume-limited collisions pi pi leftrightarrow K bar-K for the production of kaon pairs. Both descriptions can dynamically account for the suppression in the yields of rare strange particles in a limited box, being in full accordance with a canonical statistical description. Oliver Fochler; Sascha Vogel; Marcus Bleicher; Carsten Greiner; Peter Koch-Steinheimer; Zhe Xu preprint http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/2743 Fri, 12 May 2006 10:23:09 +0200 http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/2758 The transverse momentum dependence of the anisotropic flow v_2 for pi, K, nucleon, Lambda, Xi and Omega is studied for Au+Au collisions at sqrt s_NN = 200 GeV within two independent string-hadron transport approaches (RQMD and UrQMD). Although both models reach only 60% of the absolute magnitude of the measured v_2, they both predict the particle type dependence of v_2, as observed by the RHIC experiments: v_2 exhibits a hadron-mass hierarchy (HMH) in the low p_T region and a number-of-constituent-quark (NCQ) dependence in the intermediate p_T region. The failure of the hadronic models to reproduce the absolute magnitude of the observed v_2 indicates that transport calculations of heavy ion collisions at RHIC must incorporate interactions among quarks and gluons in the early, hot and dense phase. The presence of an NCQ scaling in the string-hadron model results suggests that the particle-type dependencies observed in heavy-ion collisions at intermediate p_T are related to the hadronic cross sections in vacuum rather than to the hadronization process itself, as suggested by quark recombination models. Yang Lu; Marcus Bleicher; Fuming Liu; Zuhua Liu; Paul Sorensen; Horst Stöcker; Nu Xu; Xianglei Zhu preprint http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/2758 Thu, 11 May 2006 13:17:05 +0200 http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/2775 Several observables of unbound nucleons which are to some extent sensitive to the medium modifications of nucleon-nucleon elastic cross sections in neutron-rich intermediate energy heavy ion collisions are investigated. The splitting effect of neutron and proton effective masses on cross sections is discussed. It is found that the transverse flow as a function of rapidity, the Q_zz as a function of momentum, and the ratio of halfwidths of the transverse to that of longitudinal rapidity distribution R_t/l are very sensitive to the medium modifications of the cross sections. The transverse momentum distribution of correlation functions of two-nucleons does not yield information on the in-medium cross section. Qingfeng Li; Zhuxia Li; Sven Soff; Marcus Bleicher; Horst Stöcker preprint http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/2775 Wed, 10 May 2006 09:28:02 +0200 http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/2774 The Lee-Yang zeroes method is applied to study elliptic flow (v_2) in Au+Au collisions at sqrt s =200 A GeV, with the UrQMD model. In this transport approach, the true event plane is known and both the nonflow effects and event-by-event v_2 fluctuations exist. Although the low resolutions prohibit the application of the method for most central and peripheral collisions, the integral and differential elliptic flow from the Lee-Yang zeroes method agrees with the exact v_2 values very well for semi-central collisions. Xianglei Zhu; Marcus Bleicher; Horst Stöcker preprint http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/2774 Wed, 10 May 2006 09:24:16 +0200 http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/2773 We propose to measure correlations of heavy-flavor hadrons to address the status of thermalization at the partonic stage of light quarks and gluons in high-energy nuclear collisions, shown on the example of azimuthal correlations of D-Dbar pairs. We show that hadronic interactions at the late stage can not disturb these correlations significantly. Thus, a decrease or the complete absence of these initial correlations indicates frequent interactions of heavy-flavor quarks in the partonic stage. Therefore, early thermalization of light quarks is likely to be reached. PACS numbers: 25.75.-q Xianglei Zhu; Marcus Bleicher; Shengli Huang; Kai Oliver Schweda; Horst Stöcker; Hermine K. Wöhri; Nu Xu; Pengfei Zhuang preprint http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/2773 Tue, 09 May 2006 15:59:18 +0200 http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/2772 In this paper we derive a formula for the energy loss due to elastic N to N particle scattering in models with extra dimensions that are compactified on a radius R. In contrast to a previous derivation we also calculate additional terms that are suppressed by factors of frequency over compactification radius. In the limit of a large compactification radius R those terms vanish and the standard result for the non compactified case is recovered. Benjamin Koch; Marcus Bleicher preprint http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/2772 Tue, 09 May 2006 15:51:05 +0200 http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/2779 The pion source as seen through HBT correlations at RHIC energies is investigated within the UrQMD approach. We find that the calculated transverse momentum, centrality, and system size dependence of the Pratt-HBT radii R_L and R_S are reasonably well in line with experimental data. The predicted R_O values in central heavy ion collisions are larger as compared to experimental data. The corresponding quantity sqrt R_O^2-R_S^2 of the pion emission source is somewhat larger than experimental estimates. Qingfeng Li; Marcus Bleicher; Horst Stöcker preprint http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/2779 Tue, 09 May 2006 15:46:37 +0200 http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/2778 The effects of classical gravitational radiation in models with large extra dimensions are investigated for ultra high energy cosmic rays (CRs). The cross sections are implemented into a simulation package (SENECA) for high energy hadron induced CR air showers. We predict that gravitational radiation from quasi-elastic scattering could be observed at incident CR energies above 10^9 GeV for a setting with more than two extra dimensions. It is further shown that this gravitational energy loss can alter the energy reconstruction for CR energies E_CR > 5 10^9 GeV. Benjamin Koch; Hans-Joachim Drescher; Marcus Bleicher preprint http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/2778 Tue, 09 May 2006 15:42:07 +0200