Neutrino magnetic moment signatures in the supernova neutrino signal

It is known that if neutrino is a Dirac fermion with magnetic moment, then νL → νR → νL transition of supernova neutrinos may occur. The first stage of such transition is due to the neutrino spin flip inside the hot dense supernova core, while the second one – due to the neutrino spin precession in the galactic magnetic field on the way from the supernova to terrestrial detectors. This can result in the detection of 60-200 MeV neutrinos simultaneously with the ”normal” supernova neutrino signal, which would be a smoking gun for the Dirac neutrino magnetic moment, μ. We argue that in case of a nearby supernova explosion (∼ 10 kpc away from the Earth) one may observe such high-energy events in Super-Kamiokande if μ & 10μB , and in a Mt-scale detector if μ & 0.5 · 10μB. Such an observation by itself, however, may be not sufficient to determine the value of the magnetic moment, because of the ignorance of the interstellar magnetic field. We point out that if in addition a deficit of the neutronization burst neutrinos is established, it would be possible to extract the value of the magnetic moment from observations. We also briefly discuss a possible Majorana magnetic moment signature due to νe → ν̄μ,τ flip inside the supernova core.