Long-range angular correlations of π, K and p in p–Pb collisions at √sNN=5.02 TeV

Angular correlations between unidentified charged trigger particles and various species of charged associated particles (unidentified particles, pions, kaons, protons and antiprotons) aremeasured by the ALICE detector in p-Pb collisions at a nucleon–nucleon centre-of-mass energy of 5.02 TeV in the transverse momentum range 0.3<pT<4GeV/c. The correlations expressed as associated yield per trigger particle are obtained in the pseudorapidity range |ηlab<0.8. Fourier coefficients are extracted from the long-range correlations projected onto the azimuthal angle difference and studied as a function of pT and in intervals of event multiplicity. In high-multiplicity events, the second-order coefficient for protons, vp2, is observed to be smaller than that for pions, vπ2, up to about pT=2GeV/c. To reduce correlations due to jets, the per-trigger yield measured in low-multiplicity events is subtracted from that in high-multiplicity events. A two-ridge structure is obtained for all particle species. The Fourier decomposition of this structure shows that the second-order coefficients for pions and kaons are similar. The vp2 is found to be smaller at low pT and larger at higher pT than vπ2, with a crossing occurring at about 2GeV/c. This is qualitatively similar to the elliptic-flow pattern observed in heavy-ion collisions. A mass ordering effect at low transverse momenta is consistent with expectations from hydrodynamic model calculations assuming a collectively expanding system.