Components of the dilepton continuum in Pb+Pb collisions atsNN=2.76TeV

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/ψ, ψ ′ and Υ) states.Dileptons coming from hard qq 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. Because the dilepton continuum can provide quantitative information on heavy quark yields and their medium modifications, it is important to identify which dilepton sources populate different parts of the continuum. In the present study, we calculate cc and bb production and determine their contributions to the dilepton continuum in Pb+Pb collisions at √ 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 dileptons become dominant for masses greater than 10 GeV/c 2 .

Jet-dilepton conversion in expanding quark-gluon plasma

“…The end of the QGP phase occur at proper time τ c = τ i (T i /T c ) 3 , where T c =160 MeV is the critical temperature of the phase transition. We use the initial temperature T i = 370 MeV for dN/dy = 1260 at RHIC, T i = 636 MeV for dN/dy = 2400 at LHC (Pb+Pb, √ s N N =2.76 TeV), and T i = 845 MeV for dN/dy = 5624 at LHC (Pb+Pb, √ s N N =5.5 TeV) [12,13,32,33]. The numerical results of the initial conditions are presented in Table I.…”

Production of bottomonia states in proton+proton and heavy-ion collisions

“…[54]. The production cross sections for heavy flavor and quarkonia at √ s N N = 5.02 TeV [55] calculated using CEM are given in Table 5. The bottom quark production cross section is calculated to NLO in pQCD using the CT10 parton densities [56].…”

Photon production in Pb + Pb collisions at sNN=2.76 TeV

“…dN/dy is the hadron multiplicity. By using the Glauber simulation and the CMS experimental results [42,43,44,45,46], the initial conditions are presented in the Table I. Since the emission of thermal photons is sensitive to the initial conditions, we fix the value of the initial time [1,45] as τ 0 =0.15 fm/c.…”