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

Abstract

We present a theoretical study of the medium modifications of the \(p_\textrm{T}\) balance (\(x_\textrm{J}\)) of dijets in Xe+Xe collisions at \(\sqrt{s_\textrm{NN}}=5.44\) 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 \(x_\textrm{J}\) 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 \(x_\textrm{J}\) contributes to the imbalance of the dijet; in particular, the \(q_1g_2\) (quark-jet-leading) dijets experience more significant asymmetric energy loss than the \(g_1q_2\) (gluon-jet-leading) dijets traversing the QGP. By comparing the \(\Delta \langle x_\textrm{J}\rangle = \langle x_\textrm{J} \rangle _\textrm{pp} - \langle x_\textrm{J} \rangle _\textrm{AA}\) of inclusive, \(c\bar{c}\) and \(b\bar{b}\) dijets in Xe+Xe collisions, we observe \(\Delta \langle x_\textrm{J} \rangle _\mathrm{incl.}>\Delta \langle x_\textrm{J} \rangle _\mathrm{c\bar{c}}>\Delta \langle x_\textrm{J} \rangle _\mathrm{b\bar{b}}\). Moreover, \(\rho _\textrm{Xe, Pb}\), 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.