Transverse momentum balance of dijets in Xe+Xe collisions at the LHC

Abstract

We present a theoretical study of the medium modifications of the $p_T$ balance ($x_J$) of dijets in Xe+Xe collisions at $\sqrt{s_{NN}}=5.44$ TeV. The initial production of dijets was carried out using the POWHEG+PYTHIA8 prescription, which matches the next-to-leading-order (NLO) QCD matrix elements with the parton shower (PS) effect. The SHELL model described the in-medium evolution of nucleus-nucleus collisions using a transport approach. The theoretical results of the dijet $x_J$ in the Xe+Xe collisions exhibit more imbalanced distributions than those in the p+p collisions, consistent with recently reported ATLAS data. By utilizing the Interleaved Flavor Neutralisation, an infrared-and-collinear-safe jet flavor algorithm, to identify the flavor of the reconstructed jets, we classify dijets processes into three categories: gluon-gluon ($gg$), quark-gluon ($qg$), and quark-quark ($qq$), and investigated the respective medium modification patterns and fraction changes of the $gg$, $qg$, and $qq$ components of the dijet sample in Xe+Xe collisions. It is shown that the increased fraction of $qg$ component at a small $x_J$ contributes to the imbalance of the dijet; in particular, the $q_1{g}_2$ (quark-jet-leading) dijets experience more significant asymmetric energy loss than the $g_1{q}_2$ (gluon-jet-leading) dijets traversing the QGP. By comparing the $\Delta ⟨x_J⟩=⟨x_J{⟩}_{pp}-⟨x_J{⟩}_{AA}$ of inclusive, $c\bar{c}$ and $b\bar{b}$ dijets in Xe+Xe collisions, we observe $\Delta ⟨x_J{⟩}_{incl.}>\Delta ⟨x_J{⟩}_{c\bar{c}}>\Delta ⟨x_J{⟩}_{b\bar{b}}$. Moreover, ${\rho }_{Xe,Pb}$, the ratios of the nuclear modification factors of dijets in Xe+Xe to those in Pb+Pb, were calculated, which indicates that the yield suppression of dijets in Pb+Pb is more pronounced than that in Xe+Xe owing to the larger radius of the lead nucleus.

Comments: 8 pages, 6 figures