Combination of inclusive top-quark pair production cross-section measurements using ATLAS and CMS data at √s = 7 and 8 TeV

Abstract

Abstract

A combination of measurements of the inclusive top-quark pair production cross-section performed by ATLAS and CMS in proton–proton collisions at centre-of-mass energies of 7 and 8 TeV at the LHC is presented. The cross-sections are obtained using top-quark pair decays with an opposite-charge electron–muon pair in the final state and with data corresponding to an integrated luminosity of about 5 fb−1 at

s

$$ \sqrt{s} $$ = 7 TeV and about 20 fb−1 at

s

$$ \sqrt{s} $$ = 8 TeV for each experiment. The combined cross-sections are determined to be 178.5 ± 4.7 pb at

s

$$ \sqrt{s} $$ = 7 TeV and

243.3

− 5.9

+ 6.0

$$ {243.3}_{-5.9}^{+6.0} $$ pb at

s

$$ \sqrt{s} $$ = 8 TeV with a correlation of 0.41, using a reference top-quark mass value of 172.5 GeV. The ratio of the combined cross-sections is determined to be R8/7 = 1.363 ± 0.032. The combined measured cross-sections and their ratio agree well with theory calculations using several parton distribution function (PDF) sets. The values of the top-quark pole mass (with the strong coupling fixed at 0.118) and the strong coupling (with the top-quark pole mass fixed at 172.5 GeV) are extracted from the combined results by fitting a next-to-next-to-leading-order plus next-to-next-to-leading-log QCD prediction to the measurements. Using a version of the NNPDF3.1 PDF set containing no top-quark measurements, the results obtained are

m t pole

=

173.4

− 2.0

+ 1.8

$$ {m}_t^{\textrm{pole}}={173.4}_{-2.0}^{+1.8} $$ GeV and

α s

m Z

=

0.1170

− 0.0018

+ 0.0021

$$ {\alpha}_{\textrm{s}}\left({m}_Z\right)={0.1170}_{-0.0018}^{+0.0021} $$ .