Latest documents http://publikationen.stub.uni-frankfurt.de/index/index/ Fri, 16 Feb 2007 14:41:50 +0100 Fri, 16 Feb 2007 14:41:50 +0100 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 http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/2777 We discuss modifications of the neutrino-nucleon cross section due to a minimal length scale. It is shown that the enhancement of the nu-N cross section due to new physics is suppressed. Especially the potential observation rate of micro black holes at neutrino telescopes is strongly reduced. Ulrich Harbach; Marcus Bleicher preprint http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/2777 Tue, 09 May 2006 15:36:23 +0200 http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/2866 We study the transverse expansion in central Pb+Pb collisions at the CERN SPS. Strong collective motion of hadrons can be created. This flow is mainly due to meson baryon rescattering. It allows to study the angular distribution of intermediate mass meson baryon interactions. Marcus Bleicher; Christian Spieles; Christoph Ernst; Lars Gerland; Sven Soff; Horst Stöcker; Walter Greiner; Steffen A. Bass preprint http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/2866 Tue, 28 Mar 2006 15:17:34 +0200 http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/2971 In the framework of RQMD we investigate antiproton observables in massive heavy ion collisions at AGS energies and compare to preliminary results of the E878 collaboration. We focus here on the considerable influence of the real part of an antinucleon nucleus optical potential on the ¯p momentum spectra. Pacs-numbers: 14.20 Dh, 25.70.-z Christian Spieles; Marcus Bleicher; André Jahns; Raffaele Mattiello; Heinz Sorge; Horst Stöcker; Walter Greiner preprint http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/2971 Wed, 08 Feb 2006 11:26:43 +0100 http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/2970 In the framework of the relativistic quantum molecular dynamics approach (RQMD) we investigate antideuteron (d) observables in Au+Au collisions at 10.7 AGeV. The impact parameter dependence of the formation ratios d/p2 and d/p2 is calculated. In central collisions, the antideuteron formation ratio is predicted to be two orders of magnitude lower than the deuteron formation ratio. The d yield in central Au+Au collisions is one order of magnitude lower than in Si+Al collisions. In semicentral collisions di erent configuration space distributions of p s and d s lead to a large squeeze out e ect for antideuterons, which is not predicted for the p s. Marcus Bleicher; Christian Spieles; André Jahns; Raffaele Mattiello; Heinz Sorge; Horst Stöcker; Walter Greiner preprint http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/2970 Wed, 08 Feb 2006 11:18:56 +0100 http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/2994 The extension of the Periodic System into hitherto unexplored domains - anti- matter and hypermatter - is discussed. Starting from an analysis of hyperon and single hypernuclear properties we investigate the structure of multi-hyperon objects (MEMOs) using an extended relativistic meson field theory. These are contrasted with multi-strange quark states (strangelets). Their production mechanism is stud- ied for relativistic collisions of heavy ions from present day experiments at AGS and SPS to future opportunities at RHIC and LHC. It is pointed out that abso- lutely stable hypermatter is unlikely to be produced in heavy ion collisions. New attention should be focused on short lived metastable hyperclusters ( / 10 10s) and on intensity interferometry of multi-strange-baryon correlations. Lars Gerland; Christian Spieles; Marcus Bleicher; Panajotis Papazoglou; Jörg Brachmann; Adrian Dumitru; Horst Stöcker; Walter Greiner; Jürgen Schaffner; Carsten Greiner preprint http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/2994 Mon, 23 Jan 2006 11:13:19 +0100 http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/3000 We want to draw the attention to the dynamics of a (finite) hadronizing quark matter drop. Strange and antistrange quarks do not hadronize at the same time for a baryon-rich system1. Both the hadronic and the quark matter phases enter the strange sector fs 6= 0 of the phase diagram almost immediately, which has up to now been neglected in almost all calculations of the time evolution of the system. Therefore it seems questionable, whether final particle yields reflect the actual thermodynamic properties of the system at a certain stage of the evolution. We put special interest on the possible formation of exotic states, namely strangelets (multistrange quark clusters). They may exist as (meta-)stable exotic isomers of nuclear matter 2. It was speculated that strange matter might exist also as metastable exotic multi-strange (baryonic) objects (MEMO s 3). The possible creation in heavy ion collisions of long-lived remnants of the quark-gluon-plasma, cooled and charged up with strangeness by the emission of pions and kaons, was proposed in 1,4,5. Strangelets can serve as signatures for the creation of a quark gluon plasma. Currently, both at the BNL-AGS and at the CERN-SPS experiments are carried out to search for MEMO s and strangelets, e. g. by the E864, E878 and the NA52 collaborations9, Christian Spieles; Marcus Bleicher; Lars Gerland; Horst Stöcker; Carsten Greiner preprint http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/3000 Mon, 23 Jan 2006 10:28:12 +0100 http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/2991 The microscopic phasespace approach URQMD is used to investigate the stopping power and particle production in heavy systems at SPS and RHIC energies. We find no gap in the baryon rapidity distribution even at RHIC. For CERN energies URQMD shows a pile up of baryons and a supression of multi-nucleon clusters at midrapidity. Marcus Bleicher; N. Amelin; Steffen A. Bass; Mathias Brandstetter; Adrian Dumitru; Christoph Ernst; Lars Gerland; Jens Konopka; Christian Spieles; Henning Weber; L. A. Winckelmann; Horst Stöcker; Walter Greiner preprint http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/2991 Mon, 23 Jan 2006 10:08:06 +0100 http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/3004 The stopping behaviour of baryons in massive heavy ion collisions ( s k 10AGeV) is investigated within di erent microscopic models. At SPS-energies the predictions range from full stopping to virtually total transparency. Experimental data are indicating strong stopping. The initial baryo-chemical potentials and temperatures at collider energies and their impact on the formation probability of strange baryon clusters and strangelets are discussed. Lars Gerland; Christian Spieles; Marcus Bleicher; Horst Stöcker; Carsten Greiner preprint http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/3004 Thu, 19 Jan 2006 14:34:23 +0100 http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/3009 Abstract: We study transverse expansion and directed flow in Au(11AGeV)Au reactions within a multi-fluid dynamical model. Although we do not employ an equation of state (EoS) with a first order phase transition, we find a slow increase of the transverse velocities of the nucleons with time. A similar behaviour can be observed for the directed nucleon flow. This is due to non-equilibrium e ects which also lead to less and slower conversion of longitudinal into transverse momentum. We also show that the proton rapidity distribution at CERN energies, as calculated within this model, agrees well with the preliminary NA44-data. Jörg Brachmann; Adrian Dumitru; Marcus Bleicher; Joachim A. Maruhn; Horst Stöcker; Walter Greiner preprint http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/3009 Tue, 17 Jan 2006 10:01:46 +0100 http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/3022 We discuss the early evolution of ultrarelativistic heavy-ion collisions within a multi- fluid dynamical model. In particular, we show that due to the finite mean-free path of the particles compression shock waves are smeared out considerably as compared to the one-fluid limit. Also, the maximal energy density of the baryons is much lower. We discuss the time scale of kinetic equilibration of the baryons in the central region and its relevance for directed flow. Finally, thermal emission of direct photons from the fluid of produced particles is calculated within the three-fluid model and two other simple expansion models. It is shown that the transverse momentum and rapidity spectra of photons give clue to the cooling law and the early rapidity distribution of the photon source. Adrian Dumitru; Jörg Brachmann; Marcus Bleicher; Joachim A. Maruhn; Horst Stöcker; Walter Greiner preprint http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/3022 Mon, 16 Jan 2006 10:45:00 +0100 http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/3040 A study of secondary Drell-Yan production in nuclear collisions is presented for SPS energies. In addition to the lepton pairs produced in the initial collisions of the projectile and target nucleons, we consider the potentially high dilepton yield from hard valence antiquarks in produced mesons and antibaryons. We calculate the secondary Drell-Yan contributions taking the collision spectrum of hadrons from the microscopic model URQMD. The con- tributions from meson-baryon interactions, small in hadron-nucleus interac- tions, are found to be substantial in nucleus-nucleus collisions at low dilepton masses. Preresonance collisions of partons may further increase the yields. Christian Spieles; Lars Gerland; Nils Hammon; Marcus Bleicher; Steffen A. Bass; Horst Stöcker; Walter Greiner; Carlos Lourenco; Ramona Vogt preprint http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/3040 Thu, 05 Jan 2006 09:42:26 +0100 http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/3075 Direct photon production in central Pb+Pb collisions at CERN-SPS energy is calculated within the relativistic microscopic transport model UrQMD, and within distinctly di erent versions of relativistic hydrodynamics. We find that in UrQMD the local momentum distributions of the secondaries are strongly elongated along the beam axis initially. Therefore, the preequilibrium contribution dominates the photon spectrum at transverse momenta above H 1.5 GeV. The hydrodynamics prediction of a strong correlation between the temperature and radial expansion velocities on the one hand and the slope of the transverse momentum distribution of direct photons on the other hand thus is not recovered in UrQMD. The rapidity distribution of direct photons in UrQMD reveals that the initial conditions for the longitudinal expansion of the photon source (the meson fluid ) resemble rather boostinvariance than Landau-like flow. Adrian Dumitru; Marcus Bleicher; Steffen A. Bass; Christian Spieles; Ludwig Neise; Horst Stöcker; Walter Greiner preprint http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/3075 Thu, 15 Dec 2005 11:52:03 +0100 http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/3080 We perform an event-by-event analysis of the transverse momentum distribution of final state particles in central Pb(160AGeV)+Pb collisions within a microscopic non-equilibrium transport model (UrQMD). Strong influence of rescattering is found. The extracted momentum distributions show less fluctuations in A+A collisions than in p+p reactions. This is in contrast to simplified p+p extrapolations and random walk models. Marcus Bleicher; Mohamed Belkacem; Christoph Ernst; Henning Weber; Lars Gerland; Christian Spieles; Steffen A. Bass; Horst Stöcker; Walter Greiner preprint http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/3080 Wed, 14 Dec 2005 13:32:36 +0100