Observation of associated near-side and away-side long-range correlations in root S-NN=5.02 TeV Proton-Lead collisions with the ATLAS Detector

Abstract

Two-particle correlations in relative azimuthal angle ( ) and pseudorapidity ( ) are measured in ffiffiffiffiffiffiffiffi sNN p ¼ 5:02 TeV p þ Pb collisions using the ATLAS detector at the LHC. The measurements are performed using approximately 1 b 1 of data as a function of transverse momentum (pT) and the transverse energy (EPb T ) summed over 3:1 << 4:9 in the direction of the Pb beam. The correlation function, constructed from charged particles, exhibits a long-range (2 < j j < 5) ‘‘near-side’’ ( 0) correlation that grows rapidly with increasing EPb T . A long-range ‘‘away-side’’ ( ) correlation, obtained by subtracting the expected contributions from recoiling dijets and other sources estimated using events with small EPb T , is found to match the near-side correlation in magnitude, shape (in and ) and EPb T dependence. The resultant correlation is approximately symmetric about =2, and is consistent with a dominant cos2 modulation for all EPb T ranges and particle pT.