Dielectron and heavy-quark production in inelastic and high-multiplicity proton-proton collisions at root s=13 TeV
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G. and Zmeska, J. and Zou, S. and ALICE Collaboration... Show more Show less
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Abstract
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 witth 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
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