Measurements of azimuthal anisotropies of jet production in Pb+Pb collisions at $\sqrt{s_{NN}} =$ 5.02 TeV with the ATLAS detector

TL;DR

This study measures azimuthal anisotropies of jet production in Pb+Pb collisions at 5.02 TeV, revealing insights into the path-length dependence of parton energy loss in quark-gluon plasma.

Contribution

It provides the first detailed measurement of jet azimuthal anisotropy coefficients $v_2$, $v_3$, and $v_4$ at this energy, highlighting the role of initial state fluctuations.

Findings

Nonzero $v_2$ observed in most collisions, largest at lower jet $p_T$

Small but significant $v_3$ detected, independent of $p_T$ and centrality

No significant $v_4$ signal found in the studied kinematic range

Abstract

The azimuthal variation of jet yields in heavy-ion collisions provides information about the path-length dependence of the energy loss experienced by partons passing through the hot, dense nuclear matter known as the quark-gluon plasma. This paper presents the azimuthal anisotropy coefficients $v_2$, $v_3$, and $v_4$ measured for jets in Pb+Pb collisions at $\sqrt{s_{NN}} =$ 5.02 TeV using the ATLAS detector at the LHC. The measurement uses data collected in 2015 and 2018, corresponding to an integrated luminosity of 2.2 nb$^{-1}$. The $v_n$ values are measured as a function of the transverse momentum of the jets between 71 GeV and 398 GeV and the event centrality. A nonzero value of $v_2$ is observed in all but the most central collisions. The value of $v_2$ is largest for jets with lower transverse momentum, with values up to 0.05 in mid-central collisions. A smaller, nonzero value of $v_3$ of approximately 0.01 is measured with no significant dependence on jet $p_T$ or centrality, suggesting that fluctuations in the initial state play a small but distinct role in jet energy loss. No significant deviation of $v_4$ from zero is observed in the measured kinematic region.