Measurement of dielectrons in pp, p–Pb and Pb–Pb collisions with ALICE at the LHC

Alberto Calivà

doi:10.1088/1742-6596/779/1/012052

Abstract

Dielectrons are penetrating probes which carry unaffected information on the hot and dense medium created in ultra-relativistic heavy-ion collisions. The low-mass region of the dielectron spectrum (mπ0 < mee < mρ) is sensitive to virtual photon production and in-medium modifications of low-mass vector meson spectral functions. These modifications are connected to the restoration of chiral symmetry, which is expected at high temperature. Dielectrons are also sensitive to heavy-flavor production.In these proceedings, we present the preliminary results of dielectron measurements in pp collisions at = 7 TeV, in p–Pb collisions at = 5.02 TeV and in central (0-10%) Pb–Pb collisions at = 2.76 TeV with the ALICE experiment at the LHC. The expected scenario and perspectives for the dielectron measurement after the ALICE upgrade are also discussed.

Highlights

Photons and dileptons are emitted continuously during the expansion of the hot and dense medium created in ultra-relativistic heavy-ion collisions [1]
Dielectrons are sensitive to heavy-flavor production. In these √proceedings, we present the prelim√inary results of dielectron measurements in pp collisions at √s = 7 TeV, in p–Pb collisions at sNN = 5.02 TeV and in central (0-10%) Pb–Pb collisions at sNN = 2.76 TeV with the ALICE experiment at the LHC
While an enhanced dielectron production is expected in Pb–Pb collisions, originating from the QGP thermal radiation and the in-medium modification of the ρ-meson, the data-to-cocktail ratio is consistent with unity within the uncertainties

Summary

Introduction

Photons and dileptons are emitted continuously during the expansion of the hot and dense medium created in ultra-relativistic heavy-ion collisions [1]. The temperature of the system can be extracted from the direct photon pT-spectrum and from the dielectron invariant-mass distribution, with the advantage that in the latter the measurement is not affected by the Doppler shift caused by the rapid expansion of the emitting source. Different regions of the dielectron spectrum are sensitive to different stages of the collision. The low-mass region (mee < mρ) is interesting for studying the production of virtual direct photons and the modifications of the ρ-meson spectral properties in the hot hadron gas phase. In Pb–Pb collisions the centrality selection has been done using the measured multiplicity in the V0 detector. Published under licence by IOP Publishing Ltd in the TPC and ITS and on the time-of-flight measurement in the TOF detector. The efficiency calculation has been based on MC simulations including a realistic description of the detector effects

Results in pp and p–Pb collisions

Results in Pb–Pb collisions

Conclusions