New limits on radiative sterile neutrino decays from a search for single photons in neutrino interactions

It has been recently shown that excess events observed by the LSND and MiniBooNE neutrino experiments could be interpreted as a signal from the radiative decay of a heavy sterile neutrino \nu_h produced in \nu_\mu neutral current-like interactions. If the \nu_h exist, it would be also produced by the \nu_\mu beam from the CERN SPS in the neutrino beam line shielding. The \nu_h's would penetrate the shielding and be observed through the decay \nu_h -> \nu \gamma, followed by the photon conversion into e+e- pair in the active target of the NOMAD detector. The \nu_h's could be also produced in the iron of the magnetic spectrometer of the CHORUS detector, located just in front of NOMAD. Considering these two sources of \nu_h's we set new constraints on \nu_h properties and exclude part of the LSND/MiniBooNE \nu_h parameter space using bounds on single photons production in neutrino reactions recently reported by the NOMAD collaboration. We find that broad bands in the parameter space are still open for more sensitive searches for the \nu_h in future neutrino experiments.Comment: 10 pages, 5 figures. Revised version to appear in PLB. Discussion of dominant NC-like production of \nu_h's adde

Limits on νμ(νe)→ντ\nu_{\mu}(\nu_{e}) \to \nu_{\tau} oscillations and tau neutrino magnetic moment from neutrino-electron scattering

The combined effect of neutrino flavor oscillations and neutrino magnetic moment on neutrino-electron scattering is discussed. It is shown, that if the tau neutrino has a (large) magnetic moment and can oscillate into a neutrino of another flavor it can be used for a sensitive search for $\nu_{\mu}(\nu_{e}) \to \nu_{\tau}$ neutrino oscillations and the tau neutrino magnetic moment in neutrino -electron scattering experiments. The combined limits on the mixing angles and the tau neutrino magnetic moment $sin^{2}2\theta_{\mu\tau}\times \mu_{\nu_{\tau}}^{2} < 1.1 \times 10^{-18}\mu_{B}^{2}$ and $sin^{2}2\theta_{e\tau}\times \mu_{\nu_{\tau}}^{2} < 2.3 \times 10^{-18}\mu_{B}^{2}$ for $\Delta m^{2} > 10~ eV^{2}$ are presented based on results of a study of the neutrino-electron elastic scattering at LAMPF. For $\nu_{\mu}\to \nu_{\tau}$ oscillations, this would results in sensitive limit of $sin^{2}2\theta_{\mu\tau} < 4 \times 10^{-6}$, assuming the tau neutrino magnetic moment being equal to the present experimental limit of $5.4 \times 10^{-7} \mu_{B}$. The tau neutrino magnetic moment would be constrained to $\mu_{\nu_{\tau}} < 1.0 \times 10^{-8} \mu_{B}$, assuming the existence of $\nu_{\mu}\to \nu_{\tau}$ oscillations with the mixing angle $sin^{2}2\theta_{\mu\tau}$ equal to the present experimental limit of 0.01 for $\Delta m^{2} > 10~ eV^{2}$.\ Under similar assumptions the corresponding limits for $\nu_{e}\to \nu_{\tau}$ oscillations could be set to $sin^{2}2\theta_{e\tau} < 8 \times 10^{-6}$ and $\mu_{\nu_{\tau}} < 3.9 \times 10^{-9}\mu_{B}$.Comment: 6 pages, 2 figures, Latex. The paper is extended to the analysis of combined effects of tau neutino magnetic moment and $\nu_{e}\to \nu_{\tau}$ oscillations from the LAMPF neutrino-electron scattering experimen

Constraints on sub-GeV hidden sector gauge bosons from a search for heavy neutrino decays

Several models of dark matter motivate the concept of hidden sectors consisting of SU(3)_C x SU(2)_L x U(1)_Y singlet fields. The interaction between our and hidden matter could be transmitted by new abelian U'(1) gauge bosons A' mixing with ordinary photons. If such A's with the mass in the sub-GeV range exist, they would be produced through mixing with photons emitted in two photon decays of \eta,\eta' neutral mesons generated by the high energy proton beam in a neutrino target. The A's would then penetrate the downstream shielding and be observed in a neutrino detector via their A'-> e+e- decays. Using bounds from the CHARM neutrino experiment at CERN that searched for an excess of e+e- pairs from heavy neutrino decays, the area excluding the \gamma - A' mixing range 10^{-7} < \epsilon < 10^{-4} for the A' mass region 1 < M_A' <500 MeV is derived. The obtained results are also used to constrain models, where a new gauge boson X interacts with quarks and leptons. New upper limits on the branching ratio as small as Br(\eta -> \gamma X) < 10^{-14} and Br(\eta' -> \gamma X) < 10^{-12} are obtained, which are several orders of magnitude more restrictive than the previous bounds from the Crystal Barrel experiment.Comment: 6 pages,5 figures. Version to appear in PLB. arXiv admin note: substantial text overlap with arXiv:1112.5438, arXiv:hep-ex/980400

Sterile neutrino decay as a common origin for LSND/MiniBooNe and T2K excess events

We point out that the excess of electron-like neutrino events recently observed by the T2K collaboration may have a common origin with the similar excess events previously reported by the LSND and MiniBooNE experiments and interpreted as a signal from the radiative decays of a sterile neutrino \nu_h with the mass around 50 MeV produced in muon neutrino neutral current (NC) interactions. In this work we assumed that the \nu_h can also be produced in tau neutrino NC reactions.Comment: 5 pages, 5 figures. Revised version accepted by PRD (Rapid Comm.) after referee's suggestions. Fig.1 added for illustratio

Tau neutrino magnetic moments from the Super-Kamiokande and ν\nu e-scattering data

Combined results on $\nu_{\mu}\to \nu_{\tau}$ oscillations and $\nu e$-scattering from the Super-Kamiokande and LAMPF experiments, respectively, limit the Dirac $\nu_{\tau}$ diagonal magnetic moment to $\mu_{\nu_{\tau}} < 1.9\times 10^{-9} \mu_{B}$. For the scheme with 3 Majorana neutrinos the LAMPF results allow the limitation of effective $\nu_{\tau}$ magnetic moment to $\mu_{\nu_{\tau}} < 7.6 \times 10^{-10}\mu_{B}$. The moments in the scheme with additional Majorana light sterile neutrinos as well as experiments on stimulated radiative neutrino conversion are also discussed.Comment: 12 pages, To appear in Phys. Lett.

Search for MeV dark photons in a light-shining-through-walls experiment at CERN

In addition to gravity, there might be another very weak interaction between the ordinary and dark matter transmitted by U'(1) gauge bosons A' (dark photons) mixing with our photons. If such A's exist, they could be searched for in a light-shining-through-a-wall experiment with a high energy electron beam. The electron energy absorption in a calorimeter (CAL1) is accompanied by the emission of bremsstrahlung A's in the reaction eZ -> eZA' of electrons scattering on nuclei due to the \gamma - A' mixing. A part of the primary beam energy is deposited in the CAL1, while the rest of the energy is transmitted by the A' through the "CAL1 wall" and deposited in another downstream calorimeter CAL2 by the e+e- pair from the A'->e+e- decay in flight. Thus, the A's could be observed by looking for an excess of events with the two-shower signature generated by a single high energy electron in the CAL1 and CAL2. A proposal to perform such an experiment to probe the still unexplored area of the mixing strength 10^{-5} < \epsilon < 10^{-3} and masses M_{A'} < 100 MeV by using 10-300 GeV electron beams from the CERN SPS is presented. The experiment can provide complementary coverage of the parameter space, which is intended to be probed by other searches. It has also a capability for a sensitive search for A's decaying invisibly to dark-sector particles, such as dark matter, which could cover a significant part of the still allowed parameter space.Comment: 10 pages, 7 figures. Discussion on a sensitive search for the A'-> invisible decay added. This work is continued in arXiv:1312.3309. To appear in PR