Precise measurement of the W boson mass with the CMS experiment
The W boson mass (mW) is a fundamental parameter of the standard model (SM) of particle physics. The SM predicts mW as a function of other precisely measured parameters of the theory, and a global fit to these parameters yields mW = 80353 ± 6 MeV, which corresponds to a precision better than 10-4.
Observing a deviation from this prediction would be a striking indirect evidence of new physics beyond the SM. Therefore, achieving a similar uncertainty in a direct measurement of mW is crucial to test the internal consistency of the theory.
The current experimental average, which combines different measurements from multiple experiments at the LEP, Tevatron, and LHC colliders, gives mW = 80369.2 ± 13.3 MeV, in fair agreement with the SM. However, few years ago the CDF Collaboration reported a new measurement with an uncertainty of 9.4 MeV, which is 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 solve this puzzle. 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 an uncertainty close to the one of the CDF result.
Prof. Umberto D'Alesio - umberto.dalesio@ca.infn.it
Dr. Nanako Kato - nanako.kato@dsf.unica.it