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v3.3.3
Speaker: Lorenzo Bianchini
Abstract: The Standard Model (SM) of particle physics can predict the mass of the W boson, the mediator of the charged-weak interaction, with a relative precision of about 80 ppm. The existence of new particles and forces exchanged in quantum loops could however shift the W boson mass value with respect to its SM prediction. Thus, a direct measurement of the W mass can be seen as both a test of self-consistency of the SM as well as an opportunity to unveil new physics. In this respect, great interest was raised by the measurement delivered by the CDF Collaboration in 2022, which disagrees with the SM and is also barely consistent with previous measurements. Up until recently, the Compact Muon Solenoid (CMS) experiment at the LHC was the last missing contributor to the W boson mass effort. The new result by CMS, which I will present in this seminar, is based on a partial sample of LHC proton-proton collision data collected in 2016, providing the largest sample size for a W mass measurement. The W boson mass is extracted using single-muon events via a highly granular maximum likelihood fit of the muon kinematics split by charge and by relying on state-of-the-art tools for the modeling of W boson production and decay. This novel approach enables significant in-situ constraints of experimental and theoretical uncertainties. The CMS result has an uncertainty comparable to the CDF measurement and agrees with the SM. It represents a crucial step in solving the W boson mass puzzle.