Measurement of flow harmonics correlations with mean transverse momentum in lead-lead and proton-lead collisions at $\sqrt{s_{NN}}=5.02$ TeV with the ATLAS detector

The ATLAS collaboration
Aad, Georges , Abbott, Brad , Abbott, Dale Charles , Abed Abud, Adam , Abeling, Kira , Abhayasinghe, Deshan Kavishka , Abidi, Syed Haider , Abouzeid, Ossama , Abraham, Nicola , Abramowicz, Halina
Eur.Phys.J.C 79 (2019) 985, 2019.

Abstract (data abstract)
CERN-LHC. To assess the properties of the quark–gluon plasma formed in ultrarelativistic ion collisions, the ATLAS experiment at the LHC measures a correlation between the mean transverse momentum and the flow harmonics. The analysis uses data samples of lead--lead and proton--lead collisions obtained at the centre-of-mass energy per nucleon pair of 5.02~TeV, corresponding to total integrated luminosities of $22~\mu\text{b}^{-1}$ and $28~\text{nb}^{-1}$, respectively. The measurement is performed using a modified Pearson correlation coefficient with the charged-particle tracks on an event-by-event basis. The modified Pearson correlation coefficients for the 2$^{\mathrm{nd}}$-, 3$^{\mathrm{rd}}$-, and 4$^{\mathrm{th}}$-order flow harmonics are measured in the lead--lead collisions as a function of event centrality quantified as the number of charged particles or the number of nucleons participating in the collision. The measurements are performed for several intervals of the charged-particle transverse momentum. The correlation coefficients for all studied harmonics exhibit a strong centrality evolution, which only weakly depends on the charged-particle momentum range. In the proton--lead collisions, the modified Pearson correlation coefficient measured for the 2$^{\mathrm{nd}}$-order flow harmonics shows only weak centrality dependence. The lead-lead data is qualitatively described by the predictions based on the hydrodynamical model.

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