Statistical and dynamical parts of the cumulants of conserved charges in relativistic heavy ion collisions

Abstract

The Poisson-liked statistical fluctuations, which are caused by the finite number of produced particles, are firstly estimated for the cumulants of conserved charges, i.e., the cumulants of netbaryon, net-electric charge, and net-strangeness. They turn out to be the same as those baselines derived from Hadron Resonance Gas (HRG) model. The energy and centrality dependence of netproton cumulants at the Relativistic Heavy-Ion Collider (RHIC) are demonstrated to be mainly caused by statistical fluctuations. Subtracting the statistical fluctuations, the dynamical kurtosis of net-and total-proton from two versions of the AMPT model and the UrQMD model at current RHIC beam energies are presented. It is found that the observed sign change in the kurtosis of netproton can not be reproduced by these three transport models. There is no significant difference between net-and total-proton kurtosis in model calculations, in contrary to the data at RHIC.

Statistical method in quark combination model *

“…For example, we should assume more realistic quark number fluctuations and correlations in a thermal quark system in midrapidity via grand-canonical statistics or canonical statistics with Bernoulli trial selection of the midrapidity range. In addition we should also consider various effects related to finite acceptance window such as the diffusion/blur of charges during hadronization and subsequent hadronic re-scatterings as well as that caused by resonance decay [49,[54][55][56][57][58][59][60][61][62][63][64][65][66][67]. We will study these effects in this framework in the future.…”

“…Further, to make final comparison with the data of net protons, we should consider more realistic quark number fluctuations and correlations in the studied rapidity window, which may be obtained by grand-canonical statistics of the thermal quark system or by canonical statistics with a Bernoulli trial selection of the specific window. We should also consider other effects related to the finite acceptance window, such as the diffusion/blur of charges during the hadronic scatterings stage as well as that caused by resonance decay [55,58,[61][62][63][64][65][66][67][68][69][70][71][72][73]. We will study these effects in this framework in the future.…”

Isolating dynamical net-charge fluctuations

“…The first term is the average number of pairs, and the second term is the number of uncorrelated pairs. Hence the factorial cumulant isolates the correlated part of the arXiv:1809.00648v2 [nucl-th] 4 Mar 2019 variance, κ 2 , by subtracting the trivial part, N , corresponding to Poisson fluctuations [27,28]. Global conservation laws (conservation of momentum, energy, charge) give rise to correlations among particles.…”

Poisson baseline of net-charge fluctuations in relativistic heavy ion collisions

“…Under this case, the corresponding odd-order (C N 2n−1 ) and evenorder (C N 2n ) cumulants of net-charge have been derived in Ref. [12],…”

“…In experiments, the cumulants of net-proton distributions and net-charge distributions are calculated based on the data taken by the Solenoid Tracker at the Relativistic Heavy Ion Collider (RHIC/STAR) with a wide range of collision energies from √ s N N = 7.7 GeV to √ s N N = 200 GeV [8,9]. Before some interpretations from the results of cumulants measured at RHIC/STAR in terms of QCD critical phenomena, the contributions of non-critical fluctuations from other known physics must be quantified, such as the statistical fluctuations due to finite numbers of produced particles [10][11][12][13], global conservation laws in a subsystem [14], volume fluctuations [15][16][17], and experimental acceptance cuts [18,19]. It is also suggested to study the dynamical cumulants, which is the difference of the cumulants calculated from experiments and corresponding statistical fluctuations [20,21].…”