Abstract
Measurements of the W boson mass are planned by the ATLAS and CMS experiments, but for the time being, these may be unable to compete with the current world average precision of 15 MeV, due to uncertainties in the PDFs. We discuss the potential of a measurement by the LHCb experiment based on the charged lepton transverse momentum p_T^{ell } spectrum in W rightarrow mu nu decays. The unique forward acceptance of LHCb means that the PDF uncertainties would be anti-correlated with those of p_T^{ell } based measurements by ATLAS and CMS. We compute an average of ATLAS, CMS and LHCb measurements of m_W from the p_T^{ell } distribution. Considering PDF uncertainties, this average is a factor of 1.3 more precise than an average of ATLAS and CMS alone. Despite the relatively low rate of W production in LHCb, we estimate that with the Run-II dataset, a measurement could be performed with sufficient experimental precision to exploit this anti-correlation in PDF uncertainties. The modelling of the lepton-pair transverse momentum distribution in the neutral current Drell–Yan process could be a limiting factor of this measurement and will deserve further studies.
Highlights
The transverse mass, m W T =2 pTE/T (1 − cos φ), where pT is the charged lepton transverse momentum,E/T is the missing transverse energy measured by the calorimeter, which estimates the neutrino transverse momentum; and φ is the azimuthal opening angle between the neutrino and charged lepton.2
Measurements of the W boson mass are planned by the ATLAS and CMS experiments, but for the time being, these may be unable to compete with the current world average precision of 15 MeV, due to uncertainties in the parton distribution functions (PDFs)
Improving the precision on mW remains a priority in particle physics
Summary
2 pTE/T (1 − cos φ), where pT is the charged lepton transverse momentum,E/T is the missing transverse energy measured by the calorimeter, which estimates the neutrino transverse momentum; and φ is the azimuthal opening angle between the neutrino and charged lepton. The studies reported in this paper assume that ATLAS and CMS will make this requirement in their measurements. Proposed that even within the limited acceptance of the ATLAS and CMS detectors, an exploitation of the correlations between different rapidity regions and with the two W charges could reduce the uncertainty by around 60 %. The unique angular acceptance of LHCb turns out to be a complement to the ATLAS and CMS measurements when we consider the PDF uncertainties.
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