Long-range angular correlations on the near and away side in p–Pb collisions at s NN = 5.02 TeV

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,assoc < p T,trig < 4 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 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.