Probing Muonphilic Force Carriers and Dark Matter at Kaon Factories
Gordan Krnjaic, Gustavo Marques-Tavares, Diego Redigolo, Kohsaku Tobioka
Abstract
Rare kaon decays are excellent probes of light, new weakly coupled particles. If such particles $X$ couple preferentially to muons, they can be produced in $K\ensuremath{\rightarrow}\ensuremath{\mu}\ensuremath{\nu}X$ decays. We evaluate the future sensitivity for this process at NA62 assuming $X$ decays either invisibly or to dimuons. Our main physics target is the parameter space that resolves the $(g\ensuremath{-}2{)}_{\ensuremath{\mu}}$ anomaly, where $X$ is a gauged ${L}_{\ensuremath{\mu}}\ensuremath{-}{L}_{\ensuremath{\tau}}$ vector or a muonphilic scalar. The same parameter space can also accommodate dark matter freeze-out or reduce the tension between cosmological and local measurements of ${H}_{0}$ if the new force decays to dark matter or neutrinos, respectively. We show that for invisible $X$ decays, a dedicated single muon trigger analysis at NA62 could probe much of the remaining $(g\ensuremath{-}2{)}_{\ensuremath{\mu}}$ favored parameter space. Alternatively, if $X$ decays to muons, NA62 can perform a dimuon resonance search in $K\ensuremath{\rightarrow}3\ensuremath{\mu}\ensuremath{\nu}$ events and greatly improve existing coverage for this process. Independently of its sensitivity to new particles, we find that NA62 is also sensitive to the standard model predicted rate for $K\ensuremath{\rightarrow}3\ensuremath{\mu}\ensuremath{\nu}$, which has never been measured.