Components of the dilepton continuum in Pb+Pb collisions at $\sqrt{s_{_{NN}}} = 2.76 $ TeV

TL;DR

This paper analyzes the various sources contributing to the dilepton continuum in Pb+Pb collisions at 2.76 TeV, quantifying their roles and effects, especially focusing on heavy quark production, Drell-Yan, and thermal radiation.

Contribution

It provides a detailed calculation of heavy quark, Drell-Yan, and thermal dilepton contributions in heavy-ion collisions at LHC energies, including effects of heavy quark energy loss.

Findings

Heavy flavor decays dominate dilepton production across most kinematic ranges.

Drell-Yan processes become dominant at high mass and forward rapidities.

Thermal dilepton contributions are suppressed at high transverse momentum.

Abstract

The dilepton invariant mass spectrum measured in heavy-ion collisions includes contributions from important QGP probes such as thermal radiation and the quarkonium ($J/\psi$, $\psi'$ and $\Upsilon$) states. Dileptons coming from hard $q \bar q$ scattering, the Drell-Yan process, contribute in all mass regions. In heavy-ion colliders, such as the LHC, semileptonic decays of heavy flavor hadrons provide a substantial contribution to the dilepton continuum. The dilepton continuum can give quantitative information about heavy quark yields and their modification in the medium and thus it is important to know all different sources which populate the continuum. In the present study, we calculate $c \bar c$ and $b \bar b$ production and determine their contributions to the dilepton continuum in Pb+Pb collisions at $\sqrt{s_{_{NN}}} = 2.76$ TeV with and without including heavy quark energy loss. We also calculate the rates for Drell-Yan and thermal dilepton production. The contributions to the continuum from these dilepton sources are studied in the kinematic ranges relevant for the LHC detectors. The relatively high $p_T$ cutoff for single leptons excludes most dileptons produced by the thermal medium. Heavy flavors are the dominant source of dilepton production in all the kinematic regimes except at forward rapidities where Drell-Yan start dominating in high mass range beyond 10 GeV/$c^2$.