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Free keywords:
High Energy Physics - Experiment, hep-ex
MPINP:
LHCb - Abteilung Hofmann
Abstract:
A measurement of the cross-section for $W \to e\nu$ production in $pp$
collisions is presented using data corresponding to an integrated luminosity of
$2\,$fb$^{-1}$ collected by the LHCb experiment at a centre-of-mass energy of
$\sqrt{s}=8\,$TeV. The electrons are required to have more than $20\,$GeV of
transverse momentum and to lie between 2.00 and 4.25 in pseudorapidity. The
inclusive $W$ production cross-sections, where the $W$ decays to $e\nu$, are
measured to be \begin{equation*} \sigma_{W^{+} \to e^{+}\nu_{e}}=1124.4\pm
2.1\pm 21.5\pm 11.2\pm 13.0\,\mathrm{pb}, \end{equation*} \begin{equation*}
\sigma_{W^{-} \to e^{-}\bar{\nu}_{e}}=\,\,\,809.0\pm 1.9\pm 18.1\pm\,\,\,7.0\pm
\phantom{0}9.4\,\mathrm{pb}, \end{equation*} where the first uncertainties are
statistical, the second are systematic, the third are due to the knowledge of
the LHC beam energy and the fourth are due to the luminosity determination.
Differential cross-sections as a function of the electron pseudorapidity are
measured. The $W^{+}/W^{-}$ cross-section ratio and production charge asymmetry
are also reported. Results are compared with theoretical predictions at
next-to-next-to-leading order in perturbative quantum chromodynamics. Finally,
in a precise test of lepton universality, the ratio of $W$ boson branching
fractions is determined to be \begin{equation*} \mathcal{B}(W \to
e\nu)/\mathcal{B}(W \to \mu\nu)=1.020\pm 0.002\pm 0.019, \end{equation*} where
the first uncertainty is statistical and the second is systematic.
