Speaker
Description
Centrality fluctuations (CF) is one of the main uncertainties for interpreting the centrality dependence of many experimental observables. The influence of CF for any bulk observable can be studied from the multi-particle cumulants of its event by event distribution. Using a Glauber-based independent source model, we study the influence of CF on several distributions of multiplicity N and eccentricities e_n: p(N), p(e_n,e_m), p(N,e_n). In ultra-central collisions, where distribution of particle production sources is strongly distorted, we find these cumulants exhibit rich sign-change patterns, due to observable-dependent non-Gaussianity in the underlying distributions. The details of sign- change pattern change with the size of the collision systems. Simultaneous comparison on these different types cumulants between model prediction and experimental data can be used to constrain the CF and particle production mechanism in heavy-ion collisions. Since the concept of centrality and CF are expected to fluctuate in the longitudinal direction within a single event, we propose to use pseudorapidity-separated subevent cumulant method to explore the nature of intra-event fluctuations of centrality and collective dynamics. The subevent method has the potential to separate different mechanisms for multiplicity and flow fluctuations happening at different time scales. The forward detector upgrades at RHIC and LHC will greatly enhance such studies in the future.