Muon-Decay Parameters from COHERENT

We demonstrate that measurements of Coherent Elastic Neutrino-Nucleus Scattering (CE$\nu$NS) at spallation sources are valuable probes of muon-decay physics. Using COHERENT data we derive the first direct constraint on the Michel parameters governing the ${\bar{\nu }}_{\mu }$ energy distribution. We also discuss future sensitivities, the implications for the Lorentz structure of the interactions mediating muon decay and the application to other neutrino-production mechanisms like pion decay.