OPUS 4 | Universitätspublikationen

DD correlations as a sensitive probe for thermalization in high-energy nuclear collisions (2006)

Xianglei Zhu Marcus Bleicher Shengli Huang Kai Oliver Schweda Horst Stöcker Hermine K. Wöhri Nu Xu Pengfei Zhuang

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

Elliptic flow analysis at RHIC with the Lee-Yang Zeroes method in a relativistic transport approach (2006)

Xianglei Zhu Marcus Bleicher Horst Stöcker

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.

Medium modifications of the nucleon-nucleon elastic cross section in neutron-rich intermediate energy HICs (2006)

Qingfeng Li Zhuxia Li Sven Soff Marcus Bleicher Horst Stöcker

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.

No black holes at IceCube (2006)

Ulrich Harbach Marcus Bleicher

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.

Gravitational radiation from ultra high energy cosmic rays in models with large extra dimensions (2006)

Benjamin Koch Hans-Joachim Drescher Marcus Bleicher

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.

Transport model analysis of femtoscopy data at RHIC energies (2006)

Qingfeng Li Marcus Bleicher Horst Stöcker

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.

The origin of transverse flow at the SPS (1998)

Marcus Bleicher Christian Spieles Christoph Ernst Lars Gerland Sven Soff Horst Stöcker Walter Greiner Steffen A. Bass

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.

Phasespace Correlations of Antideuterons in Heavy Ion Collisions (1995)

Marcus Bleicher Christian Spieles André Jahns Raffaele Mattiello Heinz Sorge Horst Stöcker Walter Greiner

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.

Antibaryons in massive heavy ion reactions : importance of potentials (1995)

Christian Spieles Marcus Bleicher André Jahns Raffaele Mattiello Heinz Sorge Horst Stöcker Walter Greiner

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

Nucleus-nucleus collisions at highest energies (1996)

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

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.

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