Elliptic flow of thermal dileptons as a probe of QCD matter

Abstract

We study the variation of elliptic flow of thermal dileptons with a transverse momentum (${p}_{T}$) and invariant mass ($M$) for Pb+Pb collisions at $\sqrt{{s}_{\text{NN}}}=2.76$ TeV for 30$%$--40$%$ centrality. The dilepton productions from a quark gluon plasma and hot hadrons have been considered, including the spectral change of light vector mesons in the thermal bath. The space-time evolution has been carried out within the framework of (2+1)-dimensional ideal hydrodynamics with a lattice+hadron resonance gas equation of state. We find that a judicious selection of $M$ windows can be used to extract the collective properties of quark matter and hadronic matter, and also obtain a distinct signature of medium effects on vector mesons. Results within the ambit of the present work for nuclear collisions at the Large Hadron Collider (LHC) indicate a reduction of elliptic flow (${v}_{2}$) for $M$ beyond $\ensuremath{\varphi}$ mass, which, if observed experimentally, would imitate the small momentum anisotropy in the early stage of the collective motion of the partons. We also observe that the magnitude of the elliptic flow is significantly larger at LHC than at Relativistic Heavy Ion Collider (RHIC) collision conditions.