Measurement of the W boson mass with the CMS experiment

• Marco Cipriani (CERN)

Room: Aula Conversi The W boson mass (mW) is one of the fundamental parameters of the standard model (SM) of particle physics, and is closely related to several other parameters of the theory. A global fit to SM parameters predicts mW = 80353 ± 6 MeV, corresponding to a precision better than 10-4. Achieving a similar precision in a direct measurement of mW is crucial to test the internal consistency of the theory, because any observed deviation from the prediction would provide an indirect evidence of new physics beyond the SM. The current experimental average, which combines different measurements from multiple experiments at the LEP, Tevatron, and also LHC, gives mW= 80369.2 ± 13.3 MeV, in good agreement with the SM.
 However, in recent years the CDF Collaboration has reported a new measurement with an uncertainty of 9.4 MeV, currently the most precise from a single experiment but also in strong tension with the SM prediction, hinting to possible effects from new physics.
 New determinations of mW targeting the same precision as the SM prediction are thus mandatory to confirm the CDF result. This talk presents the first measurement of mW carried out by the CMS Collaboration at the LHC, using data collected at 13 TeV. Innovative experimental techniques and a novel approach to deal with theoretical uncertainties have been adopted, resulting in the most precise determination of mW at the LHC, with a precision comparable to the one of the CDF result.

The W boson mass determination: theory perspective

• Emanuele Angelo Bagnaschi (INFN LNF)

Room: Aula Conversi The determination of the W mass from the charged current Drell-Yan process is one of the cornerstones of the EW precision physics program at the LHC, due to the important function of MW in testing the consistency of the SM, and in probing BSM physics effects. In order to fulfill effectively this role, a very precise measurement is required. In that respect, the extraction of MW at a hadron collider relies heavily on theory and modelling inputs that need to be properly understood and implemented, in order to have control over theoretical and modelling uncertainties. In this talk I will review the theoretical elements that enter the W mass determination at the LHC, and I will also try to present the current understanding of the theory community in respect to theory and modelling uncertainties. Ultimately, I will also briefly show the impact of the most recent MW determinations on the BSM physics landscape.