Speaker
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 Pb+Pb collisions, indicating the possibility of the
production of such a deconfined medium in smaller collision systems.
This talk presents a comprehensive summary of 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 Δϕ and Δη, with a template fitting procedure
used to subtract the dijet contributions. Measurements of multi-particle
cumulants c_n{2−8} are also presented. The standard cumulant
measurements confirm presence of collective phenomena 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. More detailed studies
of longitudinal flow decorrelations, and higher-order cumulants in
ultra-central Pb+Pb collisions are also presented to provide deeper
insight into the details of the geometry of the initial state.
