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- 2005 (17) (remove)

#### Keywords

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#### Institute

- Elliptic flow analysis at RHIC : fluctuations vs. non-flow effects (2005)
- The cumulant method is applied to study elliptic flow (v_2) in Au+Au collisions at sqrt s=200 AGeV, with the UrQMD model. In this approach, the true event plane is known and both the non-flow effects and event-by-event spatial (epsilon) and v_2 fluctuations exist. Qualitatively, the hierarchy of v_2 's from two, four and six-particle cumulants is consistent with the STAR data, however, the magnitude of v_2 in the UrQMD model is only 60% of the data. We find that the four and six-particle cumulants are good measures of the real elliptic flow over a wide range of centralities except for the most central and very peripheral events. There the cumulant method is affected by the v_2 fluctuations. In mid-central collisions, the four and six-particle cumulants are shown to give a good estimation of the true differential v_2, especially at large transverse momentum, where the two-particle cumulant method is heavily affected by the non-flow effects.

- Determination of the fundamental scale of gravity and the number of space-time dimensions from high energetic particle interactions (2005)
- Within the ADD-model, we elaborate an idea by Vacavant and Hinchliffe and show quantitatively how to determine the fundamental scale of TeV-gravity and the number of compactified extra dimensions from data at LHC. We demonstrate that the ADD-model leads to strong correlations between the missing E_T in gravitons at different center of mass energies. This correlation puts strong constraints on this model for extra dimensions, if probed at sqr s=5.5 TeV and sqrt s=14 TeV at LHC.

- Transverse pressure and strangeness dynamics in relativistic heavy-ion reactions (2005)
- Transverse hadron spectra from proton-proton, proton-nucleus and nucleus-nucleus collisions from 2 AGeV to 21.3 ATeV are investigated within two independent transport approaches (HSD and UrQMD). For central Au+Au (Pb+Pb) collisions at energies above E lab ~ 5 AGeV, the measured K +- transverse mass spectra have a larger inverse slope parameter than expected from the default calculations. The additional pressure - as suggested by lattice QCD calculations at finite quark chemical potential mu q and temperature T - might be generated by strong interactions in the early pre-hadronic/partonic phase of central Au+Au (Pb+Pb) collisions. This is supported by a non-monotonic energy dependence of v2/pT in the present transport model.

- Excitation function of the longitudinal expansion in central nuclear collisions (2005)
- Longitudinal hadron spectra from proton-proton (pp) and nucleus-nucleus (AA) collisions from E_lab= 2 AGeV to sqrt s=200 AGeV are investigated. The widths of the rapidity spectra for various particle species increases monotonously with energy. The present calculation indicates no sign of a step like behaviour as excepted from the Kaon transverse mass systematics. For Pions, the transport simulation is consistent with a Landau type scaling of the rapidity widths, both in central AA reactions and in pp collisions. However, other hadron species do not follow the Landau scaling. The present model predicts a decreasing rapidity width with particle mass for newly produced particles, not supporting a Landau type flow interpretation.

- Dynamic canonical suppression of strangeness in transport models (2005)
- It is investigated whether canonical suppression associated with the exact conservation of an U(1)-charge can be reproduced correctly by current transport models. Therefore a pion-gas having a volume-limited cross section for kaon production and annihilation is simulated within two different transport prescriptions for realizing the inelastic collisions. It is found that both models can indeed dynamically account for the canonical suppression in the yields of rare strange particles.

- Evidence for the onset of deconfinement from longitudinal momentum distributions? : Observation of the softest point of the equation of state (2005)
- We analyze longitudinal pion spectra from E_lab= 2AGeV to sqrt s_NN=200GeV within Landau's hydrodynamical model. From the measured data on the widths of the pion rapidity spectra, we extract the sound velocity c_s 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 E_beam=30AGeV. This softening of the EoS is compatible with the assumption of the formation of a mixed phase at the onset of deconfinement.

- Probing the density dependence of the symmetry potential at low and high densities (2005)
- We investigate the sensitivity of several observables to the density dependence of the symmetry potential within the microscopic transport model UrQMD (ultrarelativistic quantum molecular dynamics model). The same systems are used to probe the symmetry potential at both low and high densities. The influence of the symmetry potentials on the yields of pi-, pi+, the pi-/pi+ ratio, the n/p ratio of free nucleons and the t/3He ratio are studied for neutron-rich heavy ion collisions (208Pb+208Pb, 132Sn+124Sn, 96Zr+96Zr) at E_b=0.4A GeV. We find that these multiple probes provides comprehensive information on the density dependence of the symmetry potential.