Hunting Down Massless Dark Photons in Kaon Physics
AbstractIf dark photons are massless, they couple to standard-model particles only via higher dimensional operators, while direct (renormalizable) interactions induced by kinetic mixing, which motivates most of the current experimental searches, are absent. We consider the effect of possible flavor-changing magnetic-dipole couplings of massless dark photons in kaon physics. In particular, we study the branching ratio for the process K+→π+π0γ¯ with a simplified-model approach, assuming the chiral quark model to evaluate the hadronic matrix element. Possible effects in the K0-K¯0 mixing are taken into account. We find that branching ratios up to O(10-7) are allowed—depending on the dark-sector masses and couplings. Such large branching ratios for K+→π+π0γ¯ could be of interest for experiments dedicated to rare K+ decays like NA62 at CERN, where γ¯ can be detected as a massless invisible system.