Measurements of long-range azimuthal anisotropies and associated Fourier coefficients for pp collisions at vs=5.02 and 13 TeV and p+Pb collisions at vsNN=5.02 TeV with the ATLAS detector

ATLAS measurements of two-particle correlations are presented for vs=5.02 and 13 TeV ppcollisions and for vsNN=5.02 TeV p+Pb collisions at the LHC. The correlation functions are measured as a function of relative azimuthal angle ??, and pseudorapidity separation ??, using charged particles detected within the pseudorapidity interval |?|<2.5. Azimuthal modulation in the long-range component of the correlation function, with |??|>2, is studied using a template fitting procedure to remove a “back-to-back” contribution to the correlation function that primarily arises from hard-scattering processes. In addition to the elliptic, cos (2??), modulation observed in a previous measurement, the pp correlation functions exhibit significant cos (3??) and cos (4??) modulation. The Fourier coefficients vn, n associated with the cos (n??) modulation of the correlation functions for n=2–4 are measured as a function of charged-particle multiplicity and charged-particle transverse momentum. The Fourier coefficients are observed to be compatible with cos (n?) modulation of per-event single-particle azimuthal angle distributions. The single-particle Fourier coefficients vn are measured as a function of charged-particle multiplicity, and charged-particle transverse momentum for n=2–4. The integrated luminosities used in this analysis are, 64nb-1 for the vs=13 TeV pp data, 170 nb-1 for the v s = 5.02 TeV pp data, and 28 nb-1 for the vsNN = 5.02 TeV p+Pb data.