Novel W-boson mass measurement provides a precise test of the Standard Model
In the Standard Model of particle physics, the masses of the Z and Wbosons (MZ, MW) are related to another parameter of the theory, namely the electroweak mixing angle θW. The parameter sin2(θW) defines the relative strengths of the weak interaction (which causes radioactive decay) and the electromagnetic interaction. Since the Zboson decays into an electron and a positron, both of which can be tracked in the detector, the Z boson's mass is precisely determined. A precise measurement of the mass of the Wboson is harder because the W boson decays into an electron and a neutrino, which does not leave a trace in the detector and therefore goes undetected. Nonetheless, Rochester researchers have carried out precise measurements of the mass of the W boson at the Tevatron. In this experiment, a team led by Prof. Arie Bodek used Tevatron-CDF data to measure the mass of the W boson indirectly by measuring sin2(θW) and by using the Standard Model relation sin2(θW) = 1 - MW2/MZ2. A comparison of the indirect and direct measurements of the mass of the W boson provides a stringent test of the Standard Model.
These CDF physicists contributed to this data analysis. From left: Arie Bodek, Jiyeon Han and Willis Sakumoto, all from the University of Rochester.