Measurements of long-range azimuthal anisotropies and associated Fourier coefficients for pp collisions at s~(1/2) = 5.02 and 13 TeV and p + Pb collisions at (s_(NN)~(1/2) = 5.02 TeV with the ATLAS detector

摘要

ATLAS measurements of two-particle correlations are presented for ~(1/2) = 5.02 and 13 TeV pp collisions and for (s_(NN)) = 5.02 TeV p + Pb collisions at the LHC. The correlation functions are measured as a function of relative azimuthal angle △Φ, and pseudorapidity separation △η, using charged particles detected within the pseudorapidity interval |η| < 2.5. Azimuthal modulation in the long-range component of the correlation function, with |△η| > 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△Φ), modulation observed in a previous measurement, the pp correlation functions exhibit significant cos(3△Φ) and cos(4△Φ) modulation. The Fourier coefficients vn,n associated with the cos(n△Φ) 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(nΦ) modulation of per-event singleparticle 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, 64 nb−1 for the s~(1/2)= 13 TeV pp data, 170 nb−1 for the s~(1/2)= 5.02 TeV pp data, and 28 nb−1 for the (s_(NN)) = 5.02 TeV p + Pb data.