Heavy neutrino decays at MiniBooNE

Abstract

It has been proposed that a sterile neutrino ν h with m h ≈ 50 MeV and a dominant decay mode ν h → νγ may be the origin of the experimental anomaly observed at LSND. We define a particular model that could also explain the MiniBooNE excess consistently with the data at other neutrino experiments (radiative muon capture at TRIUMF, T2K, or single photon at NOMAD). The key ingredients are (i) its long lifetime (τ h ≈ 3−7 × 10 −9 s), which introduces a 1/E dependence with the event energy, and (ii) its Dirac nature, which implies a photon preferably emitted opposite to the beam direction and further reduces the event energy at MiniBooNE. We show that these neutrinos are mostly produced through electromagnetic interactions with nuclei, and that T2K observations force BR(ν h → ν τ γ) ≤ 0.01 ≈ BR(ν h → ν µ γ). The scenario implies then the presence of a second sterile neutrino ν h ′ which is lighter, longer lived and less mixed with the standard flavors than ν h . Since such particle would be copiously produced in air showers through ν h → ν h ′ γ decays, we comment on the possible contamination that its photon-mediated elastic interactions with matter could introduce in dark matter experiments.

Effective Majorana neutrino decay

“…Besides the mentioned detection in colliders by lepton number violation, other kinds of searches exploiting the displaced vertex and delayed photons techniques have been proposed and are taking place at the LHC [45][46][47][48][49][50][51][52]. Also, searches in neutrino telescopes like Ice Cube [53,54] have been proposed, and the new decay modes and their relation with the explanation of several anomalies as the sub-horizontal events detected by SHALON or the anomaly in MiniBoone [55,56] are being investigated [57,58]. In astrophysical envi-ronments, the cosmic and the diffuse supernova neutrino backgrounds can be used to probe possible radiative decays and other decay modes of cosmological interest [59,60].…”

Contamination of dark matter experiments from atmospheric magnetic dipoles

“…In addition, explaining the MiniBooNE anomaly consistently with T2K data [31] requires the neutrino h to decay with 99% branching ratio into another sterile neutrino [29]-namely h 0 -through the process…”

“…Both LSND [19][20][21][22] and MiniBooNE [23][24][25][26] have observed an excess of 3 events with an electron in the final state per each 1000 charged current interactions. These excesses may be explained by the addition of two sterile neutrinos with masses around 1 eV [27] or in the 10s of MeV [28,29]. The model we introduce shall be based upon this latter interpretation, which is also able to interpret the negative result at KARMEN [30].…”

“…To reproduce the scenario discussed in [29], it is necessary that m E ij obey the hierarchy m E hh 0 ( m E h 0 h % 0:5m E hh ( m E h 0 h 0 . For the magnetic dipole moment h 0 of h 0 we obtain h 0 ¼ eg R 4 2 v R r r 4 þ 12r 2 À 13 þ ð6r 4 À 20r 2 Þ log r 2 8ðr 2 À 1Þ 3 ; with r ¼ m E =M R and taking the limit m h 0 ( m E , M R .…”

Explaining the MiniBooNE excess by a decaying sterile neutrino with mass in the 250 MeV range

“…The photon model from ref. [10] is by now excluded by searches for radiative neutrino decays from kaons by the ISTRA+ experiment [13], see also [14,15]. For other decay scenarios and related work see refs.…”