Abstract
We discuss multiplicity fluctuations of charged particles produced in nuclear collisions measured event-by-event by the NA49 experiment at CERN SPS within the Glauber Monte Carlo approach. We use the concepts of wounded nucleons and wounded quarks in the mechanism of multiparticle production to characterize multiplicity fluctuations expressed by the scaled variance of multiplicity distribution. Although Wounded Nucleon Model correctly reproduce the centrality dependence of the average multiplicity in Pb+Pb collisions, it completely fails in description of corresponding centrality dependence of scaled variance of multiplicity distribution. Using subnucleonic degrees of freedom, i.e. wounded quarks within Wounded Quark Model, it is possible to describe quite well the multiplicity distribution of charged particles produced in proton+proton interactions. However, the Wounded Quark Model with parameters describing multiplicity distribution of particles produced in proton+proton interactions substantially exceeds the average multiplicity of charged particles produced in Pb+Pb collisions. To obtain values of average multiplicities close to those experimentally measured in Pb+Pb collisions, the concept of shadowed quark sources is implemented. Wounded Quark Model with implemented shadowing source scenario reproduces the centrality dependence of scaled variance of multiplicity distribution of charged particles produced in Pb+Pb collisions in the range from the most central to mid-peripheral interactions.
Highlights
Particle interactions in collisions of relativistic ions usually lead to production of secondary particles whose number rises with increasing collision energy
Fluctuations of particle multiplicity, mean transverse momentum, transverse energy (ET ), and other global observables in heavy-ion collisions have become one of the most important topics of interest, since they provide some relevant signals for the formation of quark-gluon plasma (QGP)
Using a substantial number of particles produced in collisions of relativistic ions in the Super Proton Synchrotron (SPS) and the Large Hadron Collider (LHC) at the European Organization for Nuclear Research (CERN) and the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory, one can investigate fluctuations of various observables which may be sensitive to the transitions between hadronic and partonic phases [1,2] with use of the event-by-event method [3]
Summary
Particle interactions in collisions of relativistic ions usually lead to production of secondary particles whose number rises with increasing collision energy. It is close to unity at very central collisions; it shows a substantial difference from unity at peripheral interactions This effect is not present in commonly used models of nuclear collisions. [25] the NA49 data on centrality dependence of scaled variance of the multiplicity distribution was compared to Heavy Ion Jet INteraction Generator (HIJING) [26], Hadron String Dynamics (HSD) [27], Ultra relativistic Quantum Molecular Dynamics (UrQMD) [28], and Very Energetic NUclear Scattering (VENUS) [29] simulations. A detailed discussion of HSD and UrQMD predictions for centrality dependence of scaled variance was presented in Ref. In the Appendix we use a simple example to demonstrate the influence of a fluctuating number of sources for the final multiplicity distribution
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