The measurement of dielectron production is presented as a function of
invariant mass and transverse momentum (p(T)) at midrapidity (vertical
bar ye vertical bar < 0.8) in proton-proton (pp) collisions at a
centre-of-mass energy of root s = 13 TeV. The contributions from
light-hadron decays are calculated from their measured cross sections in
pp collisions at root s = 7 TeV or 13 TeV. The remaining continuum
stems from correlated semileptonic decays of heavy-flavour hadrons.
Fitting the data with templates from two different MC event generators,
PYTHIA and POWHEG, the charm and beauty cross sections at midrapidity
are extracted for the first time at this collision energy: d
sigma(c<(c)over bar>)/dy vertical bar(y=0) = 974 +/- 138 (stat.)
+/- 140 (syst.) +/- 214(BR) mu b and d sigma(b (b) over bar)/dy vertical
bar(y=0) = 79 +/- 14 (stat.) +/- 11 (syst.) +/- 5(BR) mu b using PYTHIA
simulations and d sigma(c (c) over bar)/dy vertical bar(y=0) = 1417 +/-
184 (stat.) +/- 204 (syst.) +/- 312(BR) mu b and d sigma(b (b) over
bar)/dy vertical bar(y=0) = 48 +/- 14 (stat.) +/- 7 (syst.) +/- 3(BR) mu
b for POWHEG. These values, whose uncertainties are fully correlated
between the two generators, are consistent with extrapolations from
lower energies. The different results obtained with POWHEG and PYTHIA
imply different kinematic correlations of the heavy-quark pairs in these
two generators. Furthermore, comparisons of dielectron spectra in
inelastic events and in events collected with a trigger on high
charged-particle multiplicities are presented in various p(T) intervals.
The differences are consistent with the already measured scaling of
light-hadron and open-charm production at high charged-particle
multiplicity as a function of p(T). Upper limits for the contribution of
virtual direct photons are extracted at 90% confidence level and found
to be in agreement with pQCD calculations. (C) 2018 The Author.
Published by Elsevier B.V.