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. In 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. Dielectron 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. Heavy-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 ($p_{\rm T,ee}$) in 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. Results 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. An 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.