Centrality dependence of forward-backward multiplicity correlation in Au+Au collisions at √ s $_{NN}$=200 GeV Yu-Liang Yan $^{1}$, Dai-Mei Zhou$^{2}$, Bao-Guo Dong1 , $^{3}$, Xiao-Mei Li$^{1}$, Hai-Liang Ma$^{1}$, Ben-Hao Sa1 , 2 , 4 ∗ 1 China Institute of Atomic Energy, P.O. Box 275(18), Beijing 102413, China 2 Institute of Particle Physics, Huazhong Normal University, Wuhan 430079, China 3 Center of Theoretical Nuclear Physics, National Laboratory of Heavy Ion Accelerator of Lanzhou, Lanzhou 730000,China 4 China Center of Advanced Science and Technology, World Laboratory, P. O. Box 8730 Beijing 100080, China We have studied the centrality dependence of charged particle forward-backward multiplicity correlation strength in Au+Au collisions at √ s NN =200 GeV with a parton and hadron cascade model, PACIAE, based on PYTHIA. The calculated results are compared with the STAR data. The experimentally observed correlation strength characters: (1) the approximately flat pseudorapidity dependence in central collisions and (2) the monotonous decrease with decreasing centrality are well reproduced. However the theoretical results are larger than the STAR data for the peripheral collisions. A discussion is given for the comparison among the different models and STAR data. A prediction for the forward-backward multiplicity correlation in Pb+Pb collisions at √ s NN =5500 GeV is also given. PACS numbers: 24.10.Lx, 24.60.Ky, 25.75.Gz The study of fluctuations and correlations has been suggested as a useful means for revealing the mechanism of particle production and Quark-Gluon-Plasma (QGP) formation in relativistic heavy ion collisions [1, 2]. Cor- relations and fluctuations of the thermodynamic quan- tities and/or the produced particle distributions may be significantly altered when the system undergoes phase transition from hadronic matter to quark-gluon matter because of the very different degrees of freedom between two matters. The experimental study of fluctuations and correla- tions becomes a hot topic in relativistic heavy ion colli- sions with the availability of high multiplicity event-by- event measurements at the CERN-SPS and BNL-RHIC. An abundant experimental data have been reported [3– 6] where a lot of new physics arise and are urgent to be studied. A lot of theoretical investigations have been reported as well [7–14]. Recently STAR collaboration have measured the charged particle forward-backward (FB) multiplicity correlation strength b in a given centrality bin size at different centralities from the most central to peripheral Au+Au collisions at √ s$_{NN}$ =200 GeV [6]. The outstand- ing features of STAR data are: where n$_{f}$ and n$_{b}$ are, respectively, the number of charged particles in forward and backward pseudorapidity bins defined relatively and symmetrically to a given pseudora- pidity η . 〈 n$_{f}$ 〉 refers to the mean value of n$_{f}$ for instance. cov( n$_{f}$ , n$_{b}$ ) and var( n$_{f}$ ) are the FB multiplicity covari- ance and forward multiplicity variance, respectively. In this paper we use the PACIAE model to study the charged particle FB multiplicity correlation strength We have used a parton and hadron cascade model, PA- CIAE, to investigate the centrality bin size dependence of charged particle multiplicity correlation in most cen- tral (5, 0-5, and 0-10%) Au+Au collisions at √ s NN =200 GeV [14]. It turned out that the correlation strength increases with increasing bin size. In [14] we follow [15] defining the charged particle FB multiplicity correlation strength b as The wounded nucleon model was used in [12] to study the correlation strength, the first two characters of STAR data were reproduced, but the third one was not. In Ref. [13], the Glauber Monte Carlo code (GMC) with a “toy” wounded-nucleon model and the Hadron-String Dynam- ics (HSD) transport approach have been used to analyze the STAR data. They used three different centrality de- terminations: the impact parameter b$_{i}$ , the number of participant (wounded) nucleons N$_{part}$ , and the charged particle multiplicity N$_{ch}$ in midrapidity | η | < 1. The first two characters of STAR data can be reproduced by the N$_{part}$ and N$_{ch}$ centrality determinations, while the third character can not. A lot of theoretical interests [11–14] has been stimulated. 3. In the peripheral collisions, the correlation strength approaches to an exponential function of Δ η . 1. In most central collisions, the correlation strength is approximately independent of the distance be- tween the centers of forward and backward pseu- dorapidity bins, Δ η . 2. The correlation strength monotonously decreases with decreasing centrality. ∗ Corresponding author: sabh@ciae.ac.cn b = 〈 n$_{f}$n$_{b}$ 〉 − 〈 n$_{f}$ 〉〈 n$_{b}$ 〉 〈 n 2 f n$_{f}$ 〉 2 = cov( n$_{f}$, n$_{b}$ ) var( n$_{f}$ ) , (1) arXiv:1001.1595v2 [nucl-th] 28 May 2010 I. INTRODUCTION