# Quark Matter 2018

May 13 – 19, 2018
Venice, Italy
Europe/Zurich timezone
The organisers warmly thank all participants for such a lively QM2018! See you in China in 2019!

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

May 15, 2018, 3:40 PM
20m
Sala Mosaici-1, 3rd Floor (Palazzo del Casinò)

### Sala Mosaici-1, 3rd Floor

#### Palazzo del Casinò

Parallel Talk Collectivity in small systems

### Speaker

Brian Cole (Columbia University (US))

### Description

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 $v_2$, 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 $\mu\mu$ 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 $v_2$ measured in Z-tagged events at $\sqrt{s}=8$ and 13 TeV is compared to the $v_2$ measured in minimum-bias collisions. They are found to be of a similar magnitude.

Collaboration ATLAS Presenter name already specified Experiment

### Primary author

Barbara Krystyna Wosiek (Institute of Nuclear Physics Polish Academy of Sciences (PL))