A new purpose for the W-boson mass measurement: Searching for New Physics in lepton+MET

We show that the mW measurement is a direct probe of New Physics (NP) contributing to ℓ+MET, independently from indirect tests via the electroweak fit. Such NP modifies the kinematic distributions used to extract mW, necessitating a simultaneous fit to mW and NP. This effect can in principle bias the mW measurement, but only to a limited extent for our considered models. Given that, we demonstrate that the agreement at high-precision with SM-predicted shapes results in bounds competitive to, if not exceeding, existing ones for two examples: anomalous W decay involving a Lμ−Lτ gauge boson and ν˜ll˜ production in the MSSM.