Transverse momentum and process dependent azimuthal anisotropies in √sNN=8.16 TeV p+Pb collisions with the ATLAS detector

Abstract

The azimuthal anisotropy of charged particles produced in √ sNN = 8.16 TeV p+Pb collisions is measured with the ATLAS detector at the LHC. The data correspond to an integrated luminosity of 165 nb−1 that was collected in 2016. Azimuthal anisotropy coefficients, elliptic v2 and triangular v3, extracted using two-particle correlations with a non-flowtemplate fit procedure, are presented as a function of particle transversemomentum (pT) between 0.5 and 50 GeV. The v2 results are also reported as a function of centrality in three different particle pT intervals. The results are reported from minimum-bias events and jet-triggered events, where two jet pT thresholds are used. The anisotropies for particles with pT less than about 2 GeV are consistent with hydrodynamic flow expectations, while the significant non-zero anisotropies for pT in the range 9–50 GeV are not explained within current theoretical frameworks. In the pT range 2– 9 GeV, the anisotropies are larger in minimum-bias than in jet-triggered events. Possible origins of these effects, such as the changing admixture of particles from hard scattering and the underlying event, are discussed.