Abstract
We probe the effective field theory extending the Standard Model with a sterile neutrino in B meson decays at B factories and lepton colliders, using angular and polarization observables. We put bounds on different effective operators characterized by their distinct Dirac–Lorentz structure, and probe the N-mediated B decays sensitivity to these interactions. We define a forward–backward asymmetry A_mathrm{FB}^{ell gamma } between the muon and photon directions for the B rightarrow mu nu gamma decay, which allows us to separate the SM contribution from the effective lepton number conserving and violating processes, mediated by a near on-shell N. Using the most stringent constraints on the effective parameter space from Belle and BaBar we find that a measurement of the final polarization P_{tau } in the rare B^-rightarrow ell ^-_{1}ell ^-_{2} pi ^+ decays can help us infer the scalar or vector interaction content in the N production or decay vertices. We find that the B meson decays are more sensitive to scalar operators.
Highlights
Besides the remarkable performance of the standard model (SM) of particle physics in describing nature, neutrino oscillations are currently the most compelling experimental evidence of the need to extend the SM in order to include mechanisms for neutrino mass generation
We find that the B meson decays are more sensitive to scalar operators
These possibly not-that-heavy degrees of freedom can be described by an EFT including them: standard model effective field theory framework extended with right-handed neutrinos (SMNEFT) [8,9,10,11], and here we concentrate on a simplified scenario with only one right-handed neutrino added [8]
Summary
Besides the remarkable performance of the standard model (SM) of particle physics in describing nature, neutrino oscillations are currently the most compelling experimental evidence of the need to extend the SM in order to include mechanisms for neutrino mass generation. In this article we focus on the simplified scenario with only one heavy Majorana neutrino N , and we neglect the effect of the renormalizable Yukawa term N Lφ giving the heavy–active neutrino mixings Ul N , given that it is strongly constrained by the naive seesaw relation Ul2N ∼ mν/MN ∼ 10−14–10−10 required to account for the light ν masses [25,26], and by the experimental constraints on a toy-like model in which the SM is extended with a massive Majorana neutral fermion, assumed to have nonnegligible mixings with the active states, without making any hypothesis on the neutrino mass generation mechanism [27, 28] Such a minimal SM extension leads to contributions to LNV observables which are already close, or even in conflict, with current data from meson and tau decays, for masses MN below 10 GeV (see [27,29] and the references therein).
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