26-30 July 2021
Europe/Berlin timezone

Studies of anisotropic flow with event-shape engineering and mean transverse momentum - flow correlations in Pb-Pb, Xe-Xe and pp collisions with ALICE

26 Jul 2021, 17:15


Parallel session talk Heavy Ion Physics T05: Heavy Ion Physics


Emil Gorm Nielsen (ALICE)


Measurements of anisotropic flow ($v_n$) provide valuable information on the properties of the quark-gluon plasma.
Along with studies of standard flow observables, one can use strong fluctuations of the anisotropic flow for an efficient selection of the events corresponding to a specific initial geometry. Another quantity with unique sensitivity to physical processes in the initial state is the Pearson correlation coefficient of anisotropic flow and the mean transverse momentum, $\rho(v_{2}^{2},[p_{\rm T}])$. In particular, recent developments in heavy-ion theory suggest that initial momentum correlations and initial geometry give rise to dramatically different evolution of $\rho(v_{2}^{2},[p_{\rm T}])$ with charged-particle multiplicity, mainly at the lowest multiplicity region not accessible in most of the LHC experiments.

In this talk, the selection technique known as Event Shape Engineering has been used to measure the elliptic and triangular flow of inclusive and identified particles ($\pi$, K, p, ${\rm K}^{\rm 0}_{\rm S}$, $\Lambda$, $\Xi$) in Pb--Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV recorded by the ALICE detector. The effect of the event-shape selection is within uncertainties independent of particle species up to $p_{\rm T} \sim 8$ GeV/$c$, and the origin of this observation is discussed. Next, we present the measurements of $\rho(v_{2}^{2},[p_{\rm T}])$ in Pb--Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV and Xe--Xe collisions at $\sqrt{s_{\rm NN}} = 5.44$ TeV as a function of centrality, and as a function of charged-particle multiplicity at midrapidity that extends to the lowest multiplicities available. In addition, the results are complemented by the same measurements in pp collisions at $\sqrt{s} = 13$ TeV, where effects related to the initial geometry are suppressed. The measurements are compared to initial state models with and without initial momentum anisotropy and discussed in context of hydrodynamical and pQCD-inspired models. Finally, a new multi-harmonic correlation coefficient $\rho(v_{2}^{2},v_{3}^{2},[p_{\rm T}])$ is presented and discussed as an alternative to resolve between different initial state models in semicentral heavy-ion collisions.

First author ALICE CC chairs
Collaboration / Activity ALICE
Email alice-cc-chairs@cern.ch

Primary authors

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