TY - JOUR
T1 - Dielectron production in proton-proton collisions at root s=7 TeV
AU - The ALICE Collaboration
AU - Acharya, S.
AU - Brücken, E. J.
AU - Chang, B.
AU - Hilden, T. E.
AU - Kim, D. J.
AU - Litichevskyi, V.
AU - Mieskolainen, M. M.
AU - Orava, R.
AU - Parkkila, J. E.
AU - Rak, J.
AU - Räsänen, S. S.
AU - Saarinen, S.
AU - Slupecki, M.
AU - Snellman, T. W.
AU - Trzaska, W. H.
AU - Vargyas, M.
AU - Viinikainen, J.
PY - 2018/9/12
Y1 - 2018/9/12
N2 - The first measurement of e(+)e(-) pair production at mid-rapidity
(vertical bar eta vertical bar(e) < 0.8) in pp collisions at root s =
7TeV with ALICE at the LHC is presented. The dielectron production is
studied as a function of the invariant mass (m(ee )< 3.3 GeV/c(2)),
the pair transverse momentum (p(T,ee) < 8 GeV/c), and the pair
transverse impact parameter (DCA(ee)), i.e., the average distance of
closest approach of the reconstructed electron and positron tracks to
the collision vertex, normalised to its resolution. The results are
compared with the expectations from a cocktail of known hadronic sources
and are well described when PYTHIA is used to generate the
heavy-flavour contributions. In the low-mass region (0.14 < m(ee)
< 1.1 GeV/c(2)), prompt and non-prompt e(+)e(-) sources can be
separated via the DCA(ee). In the intermediate-mass region (1.1 <
m(ee) < 2.7 GeV/c(2)), a double-differential fit to the data in m(ee)
and p(T,ee) and a fit of the DCA(ee) distribution allow the total cc
and bb cross sections to be extracted. Two different event generators,
PYTHIA and POWHEG, can reproduce the shape of the two-dimensional m(ee)
and p(T,ee) spectra, as well as the shape , of the DCA(ee) distribution,
reasonably well. However, differences in the c (c) over bar and b (b)
over bar cross sections are observed when using the generators to
extrapolate to full phase space. Finally, the ratio of inclusive to
decay photons is studied via the measurement of virtual direct photons
in the transverse-momentum range 1 < p(T) < 8 GeV/c. This is found
to be unity within the statistical and systematic uncertainties and
consistent with expectations from next-to-leading order perturbative
quantum chromodynamic calculations.
AB - The first measurement of e(+)e(-) pair production at mid-rapidity
(vertical bar eta vertical bar(e) < 0.8) in pp collisions at root s =
7TeV with ALICE at the LHC is presented. The dielectron production is
studied as a function of the invariant mass (m(ee )< 3.3 GeV/c(2)),
the pair transverse momentum (p(T,ee) < 8 GeV/c), and the pair
transverse impact parameter (DCA(ee)), i.e., the average distance of
closest approach of the reconstructed electron and positron tracks to
the collision vertex, normalised to its resolution. The results are
compared with the expectations from a cocktail of known hadronic sources
and are well described when PYTHIA is used to generate the
heavy-flavour contributions. In the low-mass region (0.14 < m(ee)
< 1.1 GeV/c(2)), prompt and non-prompt e(+)e(-) sources can be
separated via the DCA(ee). In the intermediate-mass region (1.1 <
m(ee) < 2.7 GeV/c(2)), a double-differential fit to the data in m(ee)
and p(T,ee) and a fit of the DCA(ee) distribution allow the total cc
and bb cross sections to be extracted. Two different event generators,
PYTHIA and POWHEG, can reproduce the shape of the two-dimensional m(ee)
and p(T,ee) spectra, as well as the shape , of the DCA(ee) distribution,
reasonably well. However, differences in the c (c) over bar and b (b)
over bar cross sections are observed when using the generators to
extrapolate to full phase space. Finally, the ratio of inclusive to
decay photons is studied via the measurement of virtual direct photons
in the transverse-momentum range 1 < p(T) < 8 GeV/c. This is found
to be unity within the statistical and systematic uncertainties and
consistent with expectations from next-to-leading order perturbative
quantum chromodynamic calculations.
KW - 114 Physical sciences
U2 - 10.1007/JHEP09(2018)064
DO - 10.1007/JHEP09(2018)064
M3 - Article
VL - 2018
JO - Journal of High Energy Physics
JF - Journal of High Energy Physics
SN - 1029-8479
IS - 9
M1 - 064
ER -