ATLAS results from lead-lead collisions at sNN=2.76TeV

AbstractAn overview of the recent results on particle production in lead–lead collisions at sNN=2.76TeV obtained with the ATLAS detector is presented. Two samples of collision events recorded in 2010 and 2011 LHC heavy-ion runs, with integrated luminosities of approximately 9μb−1 and 0.15nb−1 respectively, were used. The measurements of collective flow phenomena in lead–lead collisions, related to the initial geometry and its fluctuations, are shown providing new constraints on the initial geometry models and on hydrodynamic evolution of the system. They are complemented with studies of high-transverse momentum probes. The latter include measurements of electro-weakly interacting probes such as Z bosons and prompt photons as well as strongly interacting probes like charged hadrons, heavy quarks and jets. Yields of electro-weak probes are found to be consistent with binary collision scaling for all collision centralities. On the contrary, charged hadrons, heavy quarks and jets are suppressed in central collisions relative to peripheral events. The azimuthal angle dependence of jet yields is consistent with the expected dependence on the path length traversed by partons through the medium, while the measured jet fragmentation function shows some centrality-dependent modifications. These measurements, supplemented with the results on correlations between electro-weak probes and jets, provide new insights into the mechanism of in-medium parton energy loss