Loophole in K --> pi nu nubar Search and New Weak Leptonic Forces

Abstract

Weakly interacting K --> pi X^0 emission with m_{X^0} \simeq m_{pi^0} is out of sight of the current K^+ --> pi^+ nu nubar study, but it can be sensed by the K_L --> pi^0 nu nubar search. This evades the usual Grossman-Nir bound of B(K_L --> pi^0 nu nubar) < 1.4 x 10^-9, thus the KOTO experiment is already starting to probe New Physics. An intriguing possibility is the Z' gauge boson of a weak leptonic force that couples to L_mu - L_tau (the difference between the muon and tauon numbers), which may explain the long-standing "muon g-2" anomaly, but is constrained by nu_mu N --> nu_mu N mu^+ mu^- scattering to m_{Z'} \lesssim 400 MeV. An explicit model for K --> pi Z' is given, which illustrates the link between rare kaon and B --> K mu^+ mu^-, K^{(*)} nu nubar decays. Complementary to these searches and future lepton experiments, the LHC might discover the scalar boson phi responsible for light m_{Z'} generation via phi --> Z' Z' --> 2(mu^+ mu^-).

5 pages, 3 figures, title changed, version to appear in PRL

References in corpus (4)

• Neutrino Trident Production: A Powerful Probe of New Physics with Neutrino Beams
• Study of the decay K+ => pi+,nu,nubar in the momentum region 140<Ppi<199 MeV/c
• Improved estimates of rare K decay matrix-elements from Kl3 decays
• New measurement of the K+- --> pi+-mu+mu- decay

Cited by in corpus (10)

• Explaining $(g-2{)}_{\mu ,e}$, the KOTO anomaly and the MiniBooNE excess in an extended Higgs model with sterile neutrinos
• Study of the $K_L\to {\pi }^0\nu \overline{\nu }$ Decay at the J-PARC KOTO Experiment
• Dark sector origin of the KOTO and MiniBooNE anomalies
• Implications of $b\to s\mu \mu$ Anomalies for Future Measurements of $B\to K^{(\ast )}\nu \bar{\nu }$ and $K\to \pi \nu \bar{\nu }$
• Flavor Physics and CP Violation
• Pair production of dark particles in meson decays
• Evading the Grossman-Nir bound with $\Delta I=3/2$ new physics
• Three Exceptions to the Grossman-Nir Bound
• Imprint of a new light particle at KOTO?
• Perspectives and Outlook from HEP Window on the Universe