Measurement of long-range correlations in pp collisions characterized by presence of a Z boson with the ATLAS detector

Recent measurements of correlations between two particles separated in pseudorapidity and azimuthal angles have shown striking similarities between results obtained in pp, p+A and A+A collision systems. In the pp collision system, unlike in p+A and A+A collisions, the strength of the correlations, quantified by the anisotropy parameter v2, shows little dependence on the observed charged-particle multiplicity. Recent theoretical models suggest that this can result from an intrinsically weak correlation between the charged-particle multiplicity and the impact parameter of the pp collision. An independent handle on the impact parameter can be obtained in principle by requiring the presence of a hard-scattering process in the collision. This talk presents the first measurement of two-particle correlations in pp collisions with a presence of Z boson identified via its μμ decay channel. The analysis uses ATLAS data recorded with nominal pp luminosity with high pileup. A new procedure is used to correct for the contribution of tracks arising from pileup vertices. The multiplicity and transverse momentum dependence of the inclusive charged-particle v2 measured in Z-tagged events at s√=8 and 13 TeV is compared to the v2 measured in minimum-bias collisions. They are found to be of a similar magnitude.