Dielectron production in proton-proton and proton-lead collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV

Abstract

The first measurements of dielectron production at midrapidity ($|\hat{I}{\cdot }_{\mathrm{e}}|<0.8$) in proton-proton and proton-lead collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV at the LHC are presented. The dielectron cross section is measured with the ALICE detector as a function of the invariant mass $m_{\mathrm{ee}}$ and the pair transverse momentum $p_{\mathrm{T},\mathrm{ee}}$ in the ranges $m_{\mathrm{ee}}$ < 3.5 GeV/$c^2$ and $p_{\mathrm{T},\mathrm{ee}}$ < 8.0 GeV/$c^2$, in both collision systems. In proton-proton collisions, the charm and beauty cross sections are determined at midrapidity from a fit to the data with two different event generators. This complements the existing dielectron measurements performed at $\sqrt{s}$ = 7 and 13 TeV. The slope of the $\sqrt{s}$ dependence of the three measurements is described by FONLL calculations. The dielectron cross section measured in proton-lead collisions is in agreement, within the current precision, with the expected dielectron production without any nuclear matter effects for ${\mathrm{e}}^{+}{\mathrm{e}}^{-}$ pairs from open heavy-flavor hadron decays. For the first time at LHC energies, the dielectron production in proton-lead and proton-proton collisions are directly compared at the same $\sqrt{s_{\mathrm{NN}}}$ via the dielectron nuclear modification factor $R_{\mathrm{pPb}}$. The measurements are compared to model calculations including cold nuclear matter effects, or additional sources of dielectrons from thermal radiation.

35 pages, 9 captioned figures, 2 tables, authors from page 29, published version including addendum updates, figures at http://alice-publications.web.cern.ch/node/6224