PoS - Proceedings of Science
Volume 397 - The Ninth Annual Conference on Large Hadron Collider Physics (LHCP2021) - Heavy ions
Collectivity of soft probes in small systems
T. Bold*  on behalf of the ALICE , ATLAS , and CMS Collaborations
Full text: pdf
Pre-published on: October 20, 2021
Published on: November 17, 2021
The relativistic collisions of heavy ions revealed the existence of a new, dense and hot state of matter, the quark-gluon plasma (QGP).
Models assuming that after the collision, the QGP stage occurs and the QGP behaves like nearly perfect liquid are successful
in describing collective behaviours observed experimentally.
Prior to the LHC heavy-ion programme the collisions of smaller systems like proton-ion or proton-proton were thought to be unable to produce the QGP.
Surprisingly, experimental results obtained by the LHC experiments indicated that some signatures that were attributed to the
emergence of collectivity due to the QGP were also observed in collisions of smaller systems.
The most striking are the observation of long-range azimuthal correlations even in a relatively small multiplicity proton-proton collisions.
The origin of those effects is at the moment an open question.
Is a tiny droplet of QGP created on the way from the hard scatter to the final state or the signatures of collectivity can be explained without recalling to this phenomenon?
This report discusses recently performed measurements of collectivity in small
systems which aim at correlating soft probes with the presence of a hard process in the event.
DOI: https://doi.org/10.22323/1.397.0058
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