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

Limits on ν µ → ν τ oscillations and tau neutrino magnetic moment from 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 neutrino-electron scattering in beam dump experiments. Using the present experimental limits on the magnetic moments of tau and muon neutrinos, limit on the probability of ν µ − ν τ neutrino oscillations P (ν µ → ν τ) < 2. × 10 −6 is set at 90% C.L.. This results in limit sin 2 2θ < 4. × 10 −6 for large ∆m 2. The present experimental limit on the ν µ − ν τ oscillations constrains the magnetic moment of tau neutrino to µ ντ < 1.7 × 10 −8 µ B at 90% C.L.. 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]. The massive neutrino could manifest themselves through neutrino oscillations, while electromagnetic properties of the neutrino may be observed through its electromagnetic interactions [1]. At present the ν µ → ν τ neutrino oscillation is a subject of intensive search at the CERN SPS wide-band neutrino beam in CHORUS and NOMAD experiments [2, 3]. These searches are based on appearance of tau neutrinos in the beam of muon neutrinos, where its fraction is expected to be at the level of ∼ 10 −6 , and requires detection of the ν τ charged current interaction ν τ N → τ − X (1)