Time & Place: Nov. 8, 10:00am, Room 9409

Speaker: Prof. Jiangyong Jia (贾江涌), StonyBrook University

Title: Centrality fluctuation in heavy-ion collisions

Abstract: Volume or 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.