Low-mass dielectron measurements in pp, p-Pb and Pb-Pb collisions with ALICE at the LHC

Abstract

The production of low-mass dielectrons is one of the most promising tools to understand the properties of the quark--gluon plasma (QGP) created in ultra-relativistic heavy-ion collisions.\nIn this contribution, heavy-flavor ($\\rm c\\bar{c}$ and $\\rm b\\bar{b}$) production in pp and p--Pb collisions at $\\sqrt{s_{\\rm NN}}$ = 5.02 TeV and the soft-dielectron excess in pp collisions at $\\sqrt{s}$ = 13 TeV are presented.\nDielectron production in p--Pb collisions plays an important role to investigate initial-state effects due to the presence of the cold nuclear matter in the collision.\nHeavy-flavor production cross sections have been extracted from the intermediate mass region by fitting to the dielectron invariant mass ($m_{\\rm ee}$) and pair transverse momentum ($p_{\\rm T,ee}$)\nin pp and p--Pb collisions at $\\sqrt{s_{\\rm NN}}$ = 5.02 TeV, and the nuclear modification factor $R_{\\rm pPb}$ as a function of $m_{\\rm ee}$ is firstly extracted at the LHC energy.\nResults in pp collisions at $\\sqrt{s}$ = 13 TeV with the reduced solenoid magnetic field at 0.2 T, allowing us to test very soft dielectron production, are also presented.\nAn excess in the yields is observed at very low $p_{\\rm T,ee}$ and the observed excess is described by neither hadronic bremsstrahlung nor thermal radiation.