Limits on ν μ → ν τ oscillations and tau neutrino magnetic moment from muon neutrino - electron scattering

Limits on ν µ → ν τ oscillations and tau neutrino magnetic moment from muon neutrino-electron scattering Abstract If the tau neutrino has large magnetic moment it might be effectively used to search for ν µ − ν τ neutrino oscillations in muon neutrino-electron scattering in beam dump experiments. Using the present experimental limits on the magnetic moments of tau and muon neutrinos as corresponding values of their magnetic moments, limit on the probability of ν µ − ν τ neutrino oscillations P (ν µ → ν τ) < 2. × 10 −6 resulting in limit sin 2 2θ < 4. × 10 −6 for ∆m 2 > 10eV 2 could be obtained. The present experimental limit on the ν µ − ν τ oscillations would constrain the magnetic moment of tau neutrino to µ ντ < 1.7 × 10 −8 µ B. In the Standard Model(SM) the properties of neutrino are strictly defined: it is massless particle with zero electric charge and magnetic moment. Beyond the SM the nonzero mass of the neutrino is required for the Grand Unified Theories (for review see e.g. [1]). In addition massive tau neutrino are natural candidates for the hot component of the dark matter of the Universe. Nonzero electromagnetic properties of the neutrino are also discussed in many extantions of the SM [1]. In the simplest extension of the SM neutrinos may have masses and acquire a magnetic moment through radiative corrections [2, 3]: µ ll ′ = 3G F em ll ′ 8 √ 2π 2 = 3.2 × 10 −19 m ll ′ (eV) (1) where µ ll ′ (l, l ′ = e, µ, τ) is the neutrino magnetic moment matrix and m ll ′ is the neutrino mass matrix. The massive neutrino could manifest themselves through neutrino oscillations, while electromagnetic properties of the neutrino may be observed through its electromagnetic interactions [1].