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

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

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

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

Invisible decay of muonium: Tests of the standard model and searches for new physics

In the Standard Model there are several canonical examples of pure leptonic processes involving the muon, the electron and the corresponding neutrinos which are connected by the crossing symmetry: i) the decay of muon, ii) the inverse muon decay, and iii) the annihilation of a muon and an electron into two neutrinos. Although the first two reactions have been observed and measured since long ago, the third process, resulting in the invisible final state, has never been experimentally tested. It may go either directly, or, at low energies, via the annihilation of a muon and an electron from an atomic bound state, called muonium (M=\mu^+e^-). The M\to \nu_\mu \nu_e decay is expected to be a very rare process, with the branching fraction predicted to be Br(M\to \nu_\mu\nu_e) = 6.6 10^{-12} with respect to the ordinary muon decay rate. Using the reported experimental results on precision measurements of the positive muon lifetime by the MuLan Collaboration, we set the first limit Br(M \to invisible) < 5.7 10^{-6}, while still leaving a big gap of about six orders of magnitude between this bound and the predictions. To improve substantially the limit, we proposed to perform an experiment dedicated to the sensitive search for the M\to invisible decay. A feasibility study of the experimental setup shows that the sensitivity of the search for this decay mode in branching fraction Br(M\to invisible) at the level of 10^{-12} could be achieved. If the proposed search results in a substantially higher branching fraction than predicted, say Br(M \to invisible) < 10^{-10}, this would unambiguously indicate the presence of new physics. We point out that such a possibility may occur due the muonium-mirror muonium conversion in the mirror matter model. A result in agreement with the Standard Model prediction would be a clean check of the pure leptonic bound state annihilation.Comment: Published version, but with more detailed description of the experimental setup and modified Fig.2. Refs. adde