CMS-PAS-SMP-23-002

CMS-PAS-SMP-23-002
Measurement of the W boson mass in proton-proton collisions at $ \sqrt{s} = $ 13 TeV
CMS Collaboration
17 September 2024

Abstract: In the standard model of particle physics, the masses of the carriers of the weak interaction, the W and Z bosons, are uniquely related. Physics beyond the standard model can change this relationship through the effects of virtual particle quantum loops, thus making it of paramount importance to measure these masses with the highest possible precision. While the mass of the Z boson is known to the remarkable precision of nearly 20 parts per million (2 MeV), thanks to the CERN LEP experimental program, the W boson mass is known much less precisely. The current precision of a global fit to electroweak data, used to predict the W boson mass in the standard model, yields an uncertainty of 6 MeV, so that reaching a comparable experimental precision would be a sensitive and fundamental test of the standard model. We report the first W boson mass measurement by the CMS Collaboration at the CERN LHC, based on a data sample collected in 2016 at the proton-proton collision energy of 13 TeV. The W boson mass is measured using a sample of $ \mathrm{W}\to\mu\nu $ events via a highly granular maximum likelihood fit to the kinematical distributions of the daughter muons, separated by electric charge. The significant in-situ constraints of theoretical inputs and their corresponding uncertainties provided by this novel approach, together with an accurate determination of the experimental effects, lead to a very precise W boson mass measurement, 80 360.2 $ \pm $ 9.9 MeV, in agreement with the standard model prediction.
Links: CDS record (PDF) ; CADI line (restricted) ; These preliminary results are superseded in this paper, Submitted to Nature. The superseded preliminary plots can be found here.

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