Probing Pb+Pb collisions at SNN=2760 GeV with spectators

Abstract

There is event by event geometric as well as quantum fluctuations in the initial condition of heavy-ion collisions. The standard technique of analysing heavy-ion collisions in bins of centrality obtained from final state multiplicity averages out the various initial configurations and thus restricts the study to only a limited range of initial conditions. In this paper, we propose an additional binning in terms of total spectator neutrons in an event. This offers us a key control parameter to probe events with broader range of initial conditions providing us an opportunity to peep into events with rarer initial conditions which otherwise get masked when analysed by centrality binning alone. We find that the inclusion of spectator binning allows one to vary ε2 and ε3 independently. We observe that the standard scaling relation between v2/ε2 and 1SdNchdη exhibited by centrality bins is strongly broken by the spectator neutron bins. Further, the acoustic scaling relation between ln⁡(vn/εn) and transverse system size is also broken- the strength of the breaking being sensitive to the binning procedure. The introduction of the spectator binning allows us to tune over a wide range viscosity driven effects for events with varying initial states but similar final state multiplicity.