# 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

## TL;DR

This paper measures correlations between flow harmonics and mean transverse momentum in lead-lead and proton-lead collisions at 5.02 TeV to understand quark-gluon plasma properties, using the ATLAS detector and a modified Pearson coefficient.

## Contribution

It introduces a measurement of flow harmonic correlations with mean transverse momentum using a modified Pearson coefficient in heavy-ion collisions at the LHC.

## Key findings

- Strong centrality dependence in lead-lead collisions
- Weak centrality dependence in proton-lead collisions
- Qualitative agreement with hydrodynamical model predictions

## Abstract

To assess the properties of the quark-gluon plasma formed in heavy-ion collisions, the ATLAS experiment at the LHC measures a correlation between the mean transverse momentum and the magnitudes of 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 $22 ~\mu b^{-1}$ and $28~nb^{-1}$, 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 $2^{nd}$-, 3$^{rd}$-, and 4$^{th}$-order harmonics are measured 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 in the lead-lead collisions, which only weakly depends on the charged-particle momentum range. In the proton-lead collisions, the modified Pearson correlation coefficient measured for the second harmonics shows only weak centrality dependence. The data is qualitatively described by the predictions based on the hydrodynamical model.