The NuTeV Collaboration has observed an excess in their dimuon channel, possibly corresponding to a long-lived neutral particle with only weak interactions and which decays to muon pairs. We show that this cannot be explained by pair production of neutralinos in the target followed by their decay far downstream in the detector via a $\mathrm{LLE}$ R-parity violating operator, as suggested in the literature. In the parameter region allowed by the CERN $e^{+}{e}^{-}$ collider LEP the event rate is far too small. We propose instead a new neutralino production method via B mesons, which can fully explain the observation. This is analogous to neutrino production via $\pi$ mesons. This model can be completely tested and thus also possibly excluded with NOMAD data. If it is excluded, the NuTeV observation is most likely not due to physics beyond the standard model. Our model can also be tested at the current and future B factories. This opens up a new way of testing for a long-lived neutralino lightest supersymmetric particle at fixed-target experiments and thus the possibility of closing the gap between collider and cosmological tests of R-parity violation. We also discuss a possible explanation in terms of a neutral heavy lepton mixing with the standard model neutrinos. The flavor structure of the observation can be accounted for but the production rate is far too low.

• Received 22 June 2001

DOI:https://doi.org/10.1103/PhysRevD.65.015001