Long-range angular correlations on the near and away side in p-Pb collisions at √sNN=5.02 TeV

Abstract

Angular correlations between charged trigger and associated particles are measured by the ALICE detector in p–Pb collisions at a nucleon–nucleon centre-of-mass energy of 5.02 TeV for transverse momentum ranges within \(0.5 < p_{T,\text{assoc}} < p_{T,\text{trig}} < 4 \text{GeV}/c\). The correlations are measured over two units of pseudorapidity and full azimuthal angle in different intervals of event multiplicity, and expressed as associated yield per trigger particle. Two long-range ridge-like structures, one on the near side and one on the away side, are observed when the per-trigger yield obtained in low-multiplicity events is subtracted from the one in high-multiplicity events. The excess on the near-side is qualitatively similar to that recently reported by the CMS Collaboration, while the excess on the away-side is reported for the first time. The two-ridge structure projected onto azimuthal angle is quantified with the second and third Fourier coefficients as well as by the near-side and away-side yields and widths. The yields on the near side and on the away side are equal within the uncertainties for all studied event multiplicity and \(p_T\) bins, and the widths show no significant evolution with event multiplicity or \(p_T\). These findings suggest that the near-side ridge is accompanied by an essentially identical away-side ridge.