Indico has been upgraded to version 3.1. Details in the SSB

# Collective effects in small collisions systems

June 15, 2017
CERN
Europe/Zurich timezone
There is a live webcast for this event.

## Recent ATLAS measurements of azimuthal anisotropies in pp and p+Pb collisions

Jun 15, 2017, 9:30 AM
25m
4/3-006 - TH Conference Room (CERN)

24
Show room on map

### Speaker

Soumya Mohapatra (Columbia University (US))

### Description

The azimuthal anisotropies of particle yields observed in relativistic heavy-ion collisions have been traditionally considered as a strong evidence of the formation on a deconfined quark-gluon plasma produced in these collisions. However multiple recent measurements from the ATLAS Collaboration in $pp$ and $p$+Pb systems show similar features as those observed in A+A collisions, indicating the possibility of the production of such a deconfined medium in smaller collision systems. This talk presents a comprehensive summary of these ATLAS measurements in $pp$ collisions at 2.76, 5.02 and 13 TeV and in $p$+Pb collisions at 5.02 and 8.16 TeV. It includes measurements of two-particle hadron-hadron and muon-hadron correlations in $\Delta\phi$ and $\Delta\eta$, with a template fitting procedure used to subtract the dijet contributions. Measurements of multi-particle cumulants $c_n\{2$--$8\}$ are alsopresented. The cumulant measurements confirm presence of collectivephenomena in $p$+Pb collisions, but are biased by non-flow correlations and are not able to provide evidence for collectivity in $pp$ collisions. To address this, measurements from a new sub-event cumulant method that suppresses the contribution of non-flow effects are presented.