We point out kaon decays to multiple charged leptons as a novel probe of light dark particles X. Previously neglected channels, such as K+→π+(XX→2(e+e-)), KL→π0(XX→2(e+e-)), and KS→(XX→2(e+e-)) may have very large rates, exceeding not only the Standard Model expectations but also possible backgrounds, such as Dalitz decays of neutral pions. We apply this idea to dark sector models where the production of dark Higgses or heavy neutral leptons leads to final states with several visible dark photons. We also investigate a recently proposed model of an MeV-scale QCD axion, where the rates for kaon decays to multiple axion states are large due to the nonlinear interactions of the axion with the light mesons. In addition, we point out new probes of this axion in pion decays, such as the single production of a in π+→ν((e+)∗→e+a→e+e+e-), double production in pion capture π-+(p or D)→aa+(n or nn)→2(e+e-)+(n or nn), as well as π0→aaa→3(e+e-). The latter decay is fixed at B(π0→aaa)=1.0×10-3 for a 17 MeV axion.
Bibliographical noteFunding Information:
We would like to thank Dr. Robert Tschirhart for correspondence on the KTEV experiment and Dr. Daniele Alves for discussions about MeV-scale QCD axions. M. P. is supported in part by U.S. Department of Energy (Grant No. desc0011842). This research was supported in part by Perimeter Institute for Theoretical Physics. Research at Perimeter Institute is supported by the Government of Canada through the Department of Innovation, Science and Economic Development and by the Province of Ontario through the Ministry of Research, Innovation and Science.
© 2022 authors. Published by the American Physical Society.