Event-by-event fluctuations of the charged particle ratio from non-equilibrium transport theory

The event by event fluctuations of the ratio of positively to negatively charged hadrons are predicted within the UrQMD model. Corrections for finite acceptance and finite net charge are derived. These corrections are relevant to compare experimental data and transport model results to previous predictions. The calculated fluctuations at RHIC and SPS energies are shown to be compatible with a hadron gas. Thus, deviating by a factor of 3 from the predictions for a thermalized quark-gluon plasma.Comment: This paper clarifies the previous predictions of Jeon and Koch (hep-ph/0003168) and addresses issues raised in hep-ph/0006023. 2 Figures, 10pp, uses RevTe

Event-by-event fluctuations and the QGP

We discuss the physics underlying event-by-event fluctuations in relativistic heavy ion collisions. We will emphasize how the fluctuations of particle ratios can be utilized to explore the properties of the matter created in these collisions. In particular, we will argue that the fluctutions of the ratio of positively over negatively charged particles may serve as a unique signature for the Quark Gluon Plasma.Comment: Proceedings Quark Matter 2001, Stony Brook, NY January 200

Signatures of a minimal length scale in high precision experiments

We discuss modifications of the gyromagnetic moment of electrons and muons due to a minimal length scale combined with a modified fundamental scale $M_f$. First-order deviations from the theoretical standard model value for $g-2$ due to these String Theory-motivated effects are derived. A constraint of $M_f>577 GeV$ for the new fundamental scale is given.Comment: Proceedings of the Nuclear Physics Winter Meeting 2004, Bormio, Ital

Reconstructing ρ0\rho^0 and ω\omega mesons from non-leptonic decays in C+C at 2AGeV

We predict transverse and longitudinal momentum spectra and yields of $\rho^0$ and $\omega$ mesons reconstructed from hadron correlations in C+C reactions at 2~AGeV. The rapidity and $p_T$ distributions for reconstructable $\rho^0$ mesons differs strongly from the primary distribution, while the $\omega$'s distributions are only weakly modified. We discuss the temporal and spatial distributions of the particles emitted in the hadron channel. Finally, we report on the mass shift of the $\rho^0$ due to its coupling to the $N^*(1520)$, which is observable in both the di-lepton and $\pi\pi$ channel. Our calculations can be tested with the Hades experiment at GSI, Darmstadt

Elliptic Flow Analysis at RHIC: Fluctuations vs. Non-Flow Effects

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.Comment: 7 pages, 7 figures, revtex 4; The discussion on the non-flow effects is extended, a new figure (Fig.3) on v2-eccentricity correlation is added, accepted for publication in Phys. Rev.

A model comparison of resonance lifetime modifications, a soft equation of state and non-Gaussian effects on π−π\pi-\pi correlations at FAIR/AGS energies

HBT correlations of $\pi^--\pi^-$ pairs at FAIR/AGS energies are investigated by using the UrQMD transport model and the CRAB analyzing program. Three different possible sources (treatment of resonance lifetimes, a soft equation of state and non-Gaussian effects) to understand the HBT $R_O/R_S$ puzzle are investigated. Firstly, we find that different treatments of the resonance decay time can not resolve the HBT time-related puzzle, however it can modify the HBT radii at low transverse momenta to some extent to explain the data slightly. Secondly, with a soft equation of state with momentum dependence, the measured transverse momentum dependent HBT radii and $R_O/R_S$ ratio can be described fairly well. Thirdly, non-Gaussian effects are visible in the calculated correlation function. Using the Edgeworth expansion, one finds that the non-Gaussian effect is strongest in the longitudinal direction and weakest in the sideward direction.Comment: 18 pages, 6 figures. To be published in J.Phys.