Abstract
Measurements of two-particle correlation functions and the first five azimuthal harmonics, to , are presented, using 28 of collisions at a nucleon-nucleon center-of-mass energy of TeV measured with the ATLAS detector at the LHC. Significant long-range “ridgelike” correlations are observed for pairs with small relative azimuthal angle () and back-to-back pairs () over the transverse momentum range GeV and in different intervals of event activity. The event activity is defined by either the number of reconstructed tracks or the total transverse energy on the Pb-fragmentation side. The azimuthal structure of such long-range correlations is Fourier decomposed to obtain the harmonics as a function of and event activity. The extracted values for to 5 decrease with . The and values are found to be positive in the measured range. The is also measured as a function of and is observed to change sign around –2.0 GeV and then increase to about 0.1 for GeV. The , , and are compared to the coefficients in collisions at TeV with similar event multiplicities. Reasonable agreement is observed after accounting for the difference in the average of particles produced in the two collision systems.
9 More- Received 5 September 2014
DOI:https://doi.org/10.1103/PhysRevC.90.044906
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©2014 CERN, for the ATLAS Collaboration