Multiplicity Fluctuations In Nucleus-nucleus Collisions Research Articles

Bayesian approach to long-range correlations and multiplicity fluctuations in nucleus-nucleus collisions

The number of particles detected in a nucleus-nucleus collision strongly depends on the impact parameter of the collision. Therefore, multiplicity fluctuations, as well as rapidity correlations of multiplicities, are dominated by impact parameter fluctuations. We present a method based on Bayesian inference which allows for a robust reconstruction of fluctuations and correlations at fixed impact parameter. We apply the method to ATLAS data on the distribution of charged multiplicity and transverse energy. We argue that multiplicity fluctuations are smaller at large rapidity than around central rapidity. We suggest simple, new analyses, in order to confirm this effect.

Event-by-event fluctuations in relativistic nuclear collisions within microscopic transport approach — HSD

In this poster a review of fluctuations within a transport model approach has been presented. The scaled variances of multiplicity fluctuations in nucleus-nucleus collisions at SPS and RHIC energies within the HSD transport model have been studied. The HSD results are compared with the proton-proton data and with predictions of the hadron-resonance gas statistical model. New measurements in a wide range of energies with the large acceptance are necessary. The preliminary data of the PHENIX Collaboration for the scaled variances of the charged hadron multiplicity fluctuations measured in Au+Au at 200 GeV have been analyzed within the model of independent sources. The scanning of the energy and atomic number for the multiplicity fluctuations at the SPS energy range has been also presented.

Multiplicity fluctuations in nucleus-nucleus collisions: Dependence on energy and atomic mass number

Event-by-event multiplicity fluctuations in central C$+$C, S$+$S, In$+$In, and Pb$+$Pb as well as $p+p$ collisions at bombarding energies from 10 to 160 AGeV are studied within the hadron string dynamics and ultrarelativistic quantum molecular dynamics microscopic transport approaches. Our investigation is directly related to the future experimental program of the NA61 Collaboration at the SPS for a search of the quantum chromodynamics (QCD) critical point. The dependence on energy and atomic mass number of the scaled variances for negative, positive, and all charged hadrons is presented and compared to the results of the model of independent sources. Furthermore, the nucleus-nucleus results from the transport calculations are compared to inelastic proton-proton collisions for reference. We find a dominant role of the participant number fluctuations in nucleus-nucleus reactions at finite impact parameter $b$. To reduce the influence of the participant numbers fluctuations on the charged particle multiplicity fluctuations only the most central events have to be selected. Accordingly, the samples of the 1% most central nucleus-nucleus collisions with the largest numbers of the projectile participants are studied. The results are compared with those for collisions at zero impact parameter. A strong influence of the centrality selection criteria on the multiplicity fluctuations is pointed out. Our findings are essential for an optimal choice of colliding nuclei and bombarding energies for the experimental search of the QCD critical point.

Particle number fluctuations in high-energy nucleus-nucleus collisions from microscopic transport approaches

Event-by-event multiplicity fluctuations in nucleus-nucleus collisions are studied within the hadron-string dynamics (HSD) and ultra-relativistic quantum molecular dynamics (UrQMD) transport models. The scaled variances of negative, positive, and all charged hadrons in Pb+Pb at 158A GeV are analyzed in comparison to the data from the NA49 Collaboration. We find a dominant role of the fluctuations in the nucleon participant number for the final hadron multiplicity fluctuations. This fact can be used to check different scenarios of nucleus-nucleus collisions by measuring the final multiplicity fluctuations as a function of collision centrality. The analysis reveals surprising effects in the recent NA49 data which indicate a rather strong mixing of the projectile and target hadron production sources even in peripheral collisions.