Long-range correlations in proton-lead collisions at sqrt{s_NN} = 5.02 TeV from ATLAS

Abstract

Two-particle correlations in relative azimuth $\Delta \varphi$ and relative pseudorapidity $\Delta \eta$ are studied in p+Pb collisions at sqrt{s_NN}=5.02 TeV with the ATLAS detector at LHC. The correlations are studied as a function of charged particle pT and the collision E_T^fcal summed over 3.1 < eta < 4.9 in the direction of the Pb beam. After subtracting the known sources of correlations such as dijets, resonances and momentum conservation, estimated using events with low E_T^fcal, the resulting correlations exhibit a $\Delta \varphi$ modulation that is flat in $\Delta \eta$ out to $|\Delta \eta |=5$. The modulation is comparable in magnitude to similar modulations observed in heavy ion collisions, and can be described by a $1+2c_2\cos 2\Delta \varphi +2c_3\cos 3\Delta \varphi$ function over 0.5<pT<7 GeV in broad ranges of E_T^fcal. The correlation analysis is repeated for event classes defined by the number of reconstructed charged particles N_ch^rec. This analysis gives nearly the same result as the analysis based on E_T^fcal for the long-range correlation at the near-side ($\Delta \varphi 0$), but leads to biases in the long-range correlations at the away-side ($\Delta \varphi \sim \pi$). HIJING simulation suggests that this bias is mainly associated with the contributions from dijets which are correlated strongly with the N_ch^rec.

Proceedings for the 29th Winter Workshop On Nuclear Dynamics, February 3-10, 2013, Squaw Valley, California, USA

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