Abstract
The first measurements of dielectron production at midrapidity ($|\eta_{c}|<0.8$) in proton-proton and proton-lead collisions at $\sqrt{s_{\rm{NN}}}$ = 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 $m_{\rm{ee}}$ and the pair transverse momentum $p_{\rm{T,ee}}$ in the ranges $m_{\rm{ee}}$ < 3.5 GeV/$c^{2}$ and $p_{\rm{T,ee}}$ < 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 $\rm{e}^{+}\rm{e}^{-}$ 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 $\sqrt{s_{\rm{NN}}}$ via the dielectron nuclear modification factor $R_{\rm{pPb}}$. The measurements are compared to model calculations including cold nuclear matter effects, or additional sources of dielectrons from thermal radiation.
Highlights
ALICE [1], located at the Large Hadron Collider (LHC) at CERN, was designed to study the quark–gluon plasma (QGP), a state of matter which consists of deconfined quarks and gluons
Calculations of pp collisions scaled with A. All of these results indicate that possible cold nuclear matter (CNM) effects are small compared to the current uncertainties of the measurements for open heavyflavor production at midrapidity at the LHC
The dielectron continuum can be well described by the expected contributions from light-flavor hadron decays and calculations of e+e− pairs from heavyflavor hadron decays fitted to the data
Summary
ALICE [1], located at the Large Hadron Collider (LHC) at CERN, was designed to study the quark–gluon plasma (QGP), a state of matter which consists of deconfined quarks and gluons. At LHC energies in minimum bias (MB) p–Pb collisions at midrapidity, the measured pT differential production cross sections of single open-charm hadrons [27,28] and their decay electrons [29,30], as well as results on azimuthal correlations of D mesons and charged particles [31], are compatible over the whole pT range probed with the results in pp collisions scaled with the atomic mass number A of the Pb nucleus. The analysis of the pp data resolves the model dependence on the expected mee and pT,ee distributions of correlated e+e− pairs from open heavy-flavor hadron decays in pp collisions, used as reference for the p–Pb study This allows for the research of possible modifications to the dielectron production in p–Pb collisions due to CNM or additional final-state effects. V, the results are presented, covering the charm and beauty cross section extracted in pp collisions, comparisons of the dielectron production in pp and p–Pb collisions to the expectations from known hadron decays, and the resulting dielectron nuclear modification factors
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