Centrality and multiparticle production in ultrarelativistic nuclear collisions

Abstract

Abstract-A critical analysis of methods for selecting central events in high-energy proton-nucleus (pA) and nucleus-nucleus (AA) collisions is presented. A sample of event classes in which background fluctuations associated with the dispersion of the impact parameter of each event or the number of participant nucleons are minimal is examined. At the SPS and LHC energies, the numbers of nucleonnucleon collisions are estimated with the aid of the Monte Carlo event generators HIJING and AMPT, which take into account energy-momentum conservation, and on the basis of a non-Glauber model involving string fusion and a modified Glauber model. The results obtained in this way demonstrate the need for revising the extensively used application of the Glauber model in normalizing multiplicity yields in experimental data on pA and AA collisions in the soft region of the spectrum.

Forward-backward correlations between intensive observables

“…The influence of possible string fusion processes on this type of correlation is rather small [12]. It also has been shown, that b nn depend strongly on the method of the centrality determination and the on the width of centrality class [13][14][15].…”

Determination of classes of events in multiplicity and its relevance to centrality in high energy Pb-Pb and p-Pb collisions in different MC models

“…Difference between PDF of nucleus and proton is found experimentally [27], [28], [29] which corresponds to the decrease of the cross-section with lesser x. The same effects were considered in different models taking into account energy conservation in elementary nuclei-nuclei interactions [30], [31], [32], [33]. Configuration of HIJING used in this work is described in more details in Appendix A.…”

“…It has been experimentally determined that PDF for nucleus and for proton is different and leads to decrease of the cross-section in case of small x. The same effects were considered in different models, taking into account energy conservation in the elementary nuclei-nuclei interactions [30], [31], [32], [33]. Without gluon shadowing nuclear interactions are meant to be independent (as it is in the Glauber model).…”