Neutrino Trident Production: A Powerful Probe of New Physics with Neutrino Beams

The production of a ${ensuremath{mu}}^{+}{ensuremath{mu}}^{ensuremath{-}}$ pair from the scattering of a muon neutrino off the Coulomb field of a nucleus, known as neutrino trident production, is a subweak process that has been observed in only a couple of experiments. As such, we show that it constitutes an exquisitely sensitive probe in the search for new neutral currents among leptons, putting the strongest constraints on well-motivated and well-hidden extensions of the standard model gauge group, including the one coupled to the difference of the lepton number between the muon and tau flavor, ${L}_{ensuremath{mu}}ensuremath{-}{L}_{ensuremath{tau}}$. The new gauge boson ${Z}^{ensuremath{‘}}$, increases the rate of neutrino trident production by inducing additional $(overline{ensuremath{mu}}{ensuremath{gamma}}_{ensuremath{alpha}}ensuremath{mu})(overline{ensuremath{nu}}{ensuremath{gamma}}^{ensuremath{alpha}}ensuremath{nu})$ interactions, which interfere constructively with the standard model contribution. Existing experimental results put significant restrictions on the parameter space of any model coupled to muon number ${L}_{ensuremath{mu}}$, and disfavor a putative resolution to the muon $gensuremath{-}2$ discrepancy via the loop of ${Z}^{ensuremath{‘}}$ for any mass ${m}_{{Z}^{ensuremath{‘}}}ensuremath{gtrsim}400text{ }text{ }mathrm{MeV}$. The reach to the models’ parameter space can be widened with future searches of the trident production at high-intensity neutrino facilities such as the LBNE.