Limits on the magnetic moment of sterile neutrino and two-photon neutrino decay

Abstract

It is shown that the non-zero transition magnetic moment ( μ tran) between the sterile neutrino ( ν s ) and the muon neutrino ( ν μ ) could be effectively searched for via the Primakoff effect, in the process of ν μ Z→ ν s Z conversion in the external Coulomb field of a nucleus Z, with the subsequent ν s → ν μ + γ decay. From the recent results of the NOMAD neutrino detector at CERN a model-independent constraint of μ tran<(10 −6−10 −9) μ B is obtained depending on the value of ν s mass. For the m s ∼ O(1) GeV region these bounds are comparable with the present experimental ones on ν μ and ν e diagonal magnetic moments and are more sensitive than those on ν τ magnetic moment. Further improvement of the bounds might be interesting for understanding of the origin of the KARMEN anomaly. From the same analysis the constraint on ν τ ( ν s )→ ν μ + γ+ γ decay lifetime τ>2×10 13 s/ m ν 7 MeV) is obtained. The limit is valid for neutrino masses up to m ν ∼ O(1) GeV.