Searcharxiv⌕ Search

arXiv subjects

Marcus Bleicher

Publications and source records attributed to Marcus Bleicher.

At least 217 records · Page 12Linked to original sources
arXiv2007

Pion freeze-out as seen through HBT correlations in heavy ion collisions from FAIR/AGS to RHIC energies

We perform a systematic analysis of several HBT parameters in heavy ion collisions from $E_{\rm beam}=2$ AGeV to $\sqrt {s_{\rm NN}}=200$ GeV within the UrQMD transport approach and compare the results to experimental data where available. We find that the 'lifetime' of the emission source as calculated from $τ\sim \sqrt{R_O^{2}-R_S^{2}}$, is larger than the experimentally observed values at all investigated energies. The calculated volume of the pion source ($V_f$) is found to increase monotonously with increasing beam energy and the experimentally observed decrease of the measured $V_f$ at AGS is not seen. Finally, we calculate the mean free path $λ_f=0.5-1$ fm of pions at freeze-out and find a good description of the experimental data above the AGS energy region, supporting the suggestion of a universal kinetic decoupling criterion up to the highest RHIC energies.

nucl-th↗
arXiv2007

Black Holes at LHC?

Strategies for identifying speculative mini black hole events (due to large extra dimensions) at future colliders are reviewed. Estimates for production cross sections, Hawking radiation, di-jet suppression and multi- mono-jet emission are surveyed. We further report on a class of effective entropy formulas that could lead to the formation of a final black hole remnant state, BHR. Such BHRs could be both electrically charged and uncharged. Charged BHRs should be observable by single stiff charged tracks in the detectors. Collinear hadronic jets with a large missing transverse momentum are presented as new observable signal for electrically neutral black holes.

hep-ph↗
arXiv2007

How to Create Black Holes on Earth?

We present a short overview on the ideas of large extra-dimensions and their implications for the possible production of micro black holes in the next generation particle accelerator at CERN (Geneva, Switzerland) from this year on. In fact, the possibility of black hole production on earth is currently one of the most exciting predictions for the LHC accelerator and would change our current understanding of physics radically. While it is impossible to discuss the models and implications in full detail here, this article is thought to serve as a starting point for the interested physics students with some basic knowledge about general relativity and particle physics.

physics.ed-ph↗
arXiv2006

Transport model analysis of the transverse momentum and rapidity dependence of pion interferometry at SPS energies

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.

nucl-th↗
arXiv2006

Baryon-Strangeness Correlations from Hadron/String- and Quark-Dynamics

Baryon-strangeness correlations ($C_{BS}$) are studied with a hadron/string transport approach (UrQMD) and a dynamical quark recombination model (quark molecular dynamics, qMD) for various energies from $E_{lab}=4A$ GeV to $\sqrt{s_{NN}}=200$ GeV. As expected, we find that the hadron/string dynamics shows correlations similar to a simple hadron gas. In case of the quark molecular dynamics, we find that initially the $C_{BS}$ correlation is that of a weakly interacting QGP but changes in the process of hadronization also to the value for a hadron gas. Therefore, we conclude that the hadronization process itself makes the initial baryon strangeness correlation unobservable. To make an experimental study of this observable more feasible, we also investigate how a restriction to only charged kaons and $Λ$'s (instead of all baryons and all strange particles) influences the theoretical result on $C_{BS}$. We find that a good approximation of the full result can be obtained in this limit in the present simulation.

nucl-th↗
arXiv2006

Effect of Rescattering on Forward-Backward Correlations

We use the Ultra-relativistic Quantum Molecular Dynamic model (UrQMD v2.2) to study forward-backward fluctuations and compare our results with the data published by the PHOBOS experiment. The extracted effective cluster multiplicities show a clear centrality dependence within the present hadron-string transport approach. This behavior is not reproduced with models not taking into account final state rescattering.

nucl-th↗
arXiv2006

Theoretical Analysis of Dilepton Spectra in Heavy Ion Collisions at GSI-FAIR Energies

This paper addresses the theoretical analysis of dilepton spectra in C+C collisions at GSI-SIS energies. Theoretical predictions for the recent data of the HADES collaboration at SIS-energies are made with the help of a hadron-string transport model, the Ultra-relativistic Quantum Molecular Dynamics (UrQMD) model. A mass shift of the $ρ$ meson due to kinematical effects is discussed.

nucl-th↗
arXiv2006

Transport model analysis of particle correlations in relativistic heavy ion collisions at femtometer scales

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.

nucl-th↗
arXiv2006

Indications for Cluster Melting from Forward-Backward Charge Fluctuations at RHIC Energies

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.

nucl-th↗
arXiv2006

Gravitational Radiation from Ultra High Energy Cosmic Rays in Models with Large Extra Dimensions

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 $E_{\rm CR}\ge 5\cdot 10^9$ GeV.

astro-ph↗
arXiv2006

Elliptic Flow Analysis at RHIC with the Lee-Yang Zeroes Method in a Relativistic Transport Approach

The Lee-Yang zeroes method is applied to study elliptic flow ($v_2$) in Au+Au collisions at $\sqrt{s}=200A$~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.

nucl-th↗
arXiv2006

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

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.

nucl-th↗
arXiv2006

No Black Holes at IceCube

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.

hep-ph↗
arXiv2005

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 ($ε$) 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.

nucl-th↗
arXiv2005

Black Hole Remnants at the LHC

Within the scenario of large extra dimensions, the Planck scale is lowered to values soon accessible. Among the predicted effects, the production of TeV mass black holes at the {\sc LHC} is one of the most exciting possibilities. Though the final phases of the black hole's evaporation are still unknown, the formation of a black hole remnant is a theoretically well motivated expectation. We analyze the observables emerging from a black hole evaporation with a remnant instead of a final decay. We show that the formation of a black hole remnant yields a signature which differs substantially from a final decay. We find the total transverse momentum of the black hole event to be significantly dominated by the presence of a remnant mass providing a strong experimental signature for black hole remnant formation.

hep-ph↗
arXiv2005

Reconstructing $ρ^0$ and $ω$ mesons from non-leptonic decays in C+C at 2AGeV

We predict transverse and longitudinal momentum spectra and yields of $ρ^0$ and $ω$ mesons reconstructed from hadron correlations in C+C reactions at 2~AGeV. The rapidity and $p_T$ distributions for reconstructable $ρ^0$ mesons differs strongly from the primary distribution, while the $ω$'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 $ρ^0$ due to its coupling to the $N^*(1520)$, which is observable in both the di-lepton and $ππ$ channel. Our calculations can be tested with the Hades experiment at GSI, Darmstadt.

nucl-th↗
arXiv2005

Evidence for the Onset of Deconfinement from Longitudinal Momentum Distributions? Observation of the Softest Point of the Equation of State

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.

hep-ph↗