Transverse energy fluctuations in Pb+Pb collisions at $\sqrt{s_{NN}}$=2.76 TeV with the ATLAS detector at the LHC

A study of calorimeter energy fluctuations in Pb+Pb collisions and their dependence on centrality is presented, using an integrated luminosity of 240 mb^{−1} of Pb+Pb collisions at √s_{NN} = 2.76 TeV collected by the ATLAS detector in 2010. The fluctuations are characterized by the per-event standard deviation of the distribution of energies in single ∆η × ∆φ = 0.1 × 0.1 calorimeter towers and in windows covering larger areas of up to 11 × 11 calorimeter towers. The event-averaged standard deviations are calculated in fine bins of Forward Calorimeter (FCal) total transverse energy (ΣET) which is a measure of the collision centrality. The dependence of the mean standard deviation on the window area is also evaluated as a function of FCal ΣET . The results of these fluctuation measurements are compared to an identical analysis applied to fully-simulated HIJING events, and good agreement is found.