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Search Results: 1 - 10 of 471559 matches for " S. N. Gninenko "
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Limit on the electric charge-nonconserving $\mu^+ \to invisible$ decay
Gninenko, S. N.
High Energy Physics - Phenomenology , 2007, DOI: 10.1103/PhysRevD.76.055004
Abstract: The first limit on the branching ratio of the electric charge-nonconserving invisible muon decay $Br(\mu^+ \to invisible) < 5.2 \times 10^{-3}$ is obtained from the recently reported results on new determination of the Fermi constant from muon decays. The results of a feasibility study of a new proposed experiment for a sensitive search for this decay mode at the level of a few parts in 10^{11} are presented. Constrains on the $\tau \to invisible$ decay rate are discussed. These leptonic charge-nonconserving processes may hold in four-dimensional world in models with infinite extra dimensions, thus making their searches complementary to collider experiments probing new physics.
Constraints on dark photons from $\pi^0$ decays
Gninenko, S. N.
High Energy Physics - Phenomenology , 2013,
Abstract: Several models of dark matter suggest the existence of hidden sectors consisting of SU(3)_C x SU(2)_L x U(1)_Y singlet fields. The interaction between the ordinary and hidden sectors could be transmitted by new Abelian U'(1) gauge bosons A' (dark or hidden photons) mixing with ordinary photons. If such A's have masses below the \pi^0 meson mass, they would be produced through \gamma - A' mixing in the \pi^0 ->2\gamma - decays and be observed via their decays A' -> e+e- in a detector. Using bounds from the SINDRUM experiment at the Paul Scherrer Institute that searched for an excess of e+e- pairs in \pi^- p interactions at rest, the area excluding the \gamma - A' mixing \epsilon > 10^{-3} for the A' mass region 25 < M_{A'} < 120 MeV is derived.
The MiniBooNE anomaly and heavy neutrino decay
S. N. Gninenko
Physics , 2009, DOI: 10.1103/PhysRevLett.103.241802
Abstract: The anomaly in the low energy distribution of quasi-elastic neutrino events reported by the MiniBooNE collaboration is discussed. We show that the observed excess of electron-like events could originate from the production and decay of a heavy neutrino ($\nu_h$) in the MiniBooNE detector. The $\nu_h$ is created by mixing in $\nu_\mu$ neutral-current interactions and decays radiatively into $ \nu \gamma$ due to a transition magnetic moment between the $\nu_h$ and a light neutrino $\nu$. The energy measured in the detector arises from the subsequent conversion of the decay photon into a $\pair$ pair within the detector volume. The analysis of the energy and angular distributions of the excess events suggests that the $\nu_h$ has a mass around 500 MeV and the lifetime $\tau_{\nu_h} \lesssim 10^{-9}$ s. Existing experimental data are found to be consistent with a mixing strength between the $\nu_h$ and the $\nu_\mu$ of $|U_{\mu h}|^2 \simeq (1-4)\times 10^{-3}$ and a $\nu_h$ transition magnetic moment of $ \mu_{tr} \simeq (1- 6)\times 10^{-9} \mu_B$. Finally, we discuss the reason why no significant excess of low energy events has been observed in the recent antineutrino data.
Bound on the tau neutrino magnetic moment from the Super-Kamiokande data
S. N. Gninenko
Physics , 1999, DOI: 10.1016/S0370-2693(99)00296-8
Abstract: It is shown that recent results from the Super-Kamiokande detector constrain the tau neutrino diagonal magnetic moment to $\mu_{\nu_{\tau}} < 1.3\times 10^{-7} \mu_{B}$ for the case of $\nu_{\mu}\to \nu_{\tau}$ interpretation of the atmospheric neutrino anomaly. It is pointed out that the large magnetic moment of the tau neutrino could affect further understanding of the origin of the anomaly.
Limit on the electric charge-nonconserving $μ^+ \to invisible$ decay
S. N. Gninenko
Physics , 2007, DOI: 10.1103/PhysRevD.76.055004
Abstract: The first limit on the branching ratio of the electric charge-nonconserving invisible muon decay $Br(\mu^+ \to invisible) < 5.2 \times 10^{-3}$ is obtained from the recently reported results on new determination of the Fermi constant from muon decays. The results of a feasibility study of a new proposed experiment for a sensitive search for this decay mode at the level of a few parts in 10^{11} are presented. Constrains on the $\tau \to invisible$ decay rate are discussed. These leptonic charge-nonconserving processes may hold in four-dimensional world in models with infinite extra dimensions, thus making their searches complementary to collider experiments probing new physics.
Constraints on sub-GeV hidden sector gauge bosons from a search for heavy neutrino decays
S. N. Gninenko
Physics , 2012, DOI: 10.1016/j.physletb.2012.06.002
Abstract: 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.
On search for hidden sector photons in Super-Kamiokande
S. N. Gninenko
Physics , 2008,
Abstract: If hidden sector photons exist, they could be produced through oscillations of photons emitted by the Sun. We show that a search for these particles could be performed in Super-Kamiokande due to the presence in this detector of a large number of photomultiplier's (PMTs) with a relatively low noise and big size. These particles would penetrate the Earth shielding and would be detected by PMTs through their oscillations into real photons inside the PMTs vacuum volume. This would results in an increase of the PMT counting rate and it daily variations depending on the Earth position with respect to the Sun. The proposed search for this effect is sensitive to the photon-hidden photon mixing strength as small as ~10^{-6} for the hidden photon mass region ~10^{-3} - 10^{-1} eV and, in the case of nonobservation, could improve limits recently obtained from photon regeneration laser experiments for this mass region.
Limits on leptonic photon interactions from SN1987a
S. N. Gninenko
Physics , 1997, DOI: 10.1016/S0370-2693(97)01129-5
Abstract: If massless leptonic photons associated to electron, muon or tau leptonic number exist they would have been emitted from supernova 1987a via the annihilation process $\nu\bar{\nu}\to\gamma_{l}\gamma_{l}$. By requiring that this process does not carry away most of the energy that can be radiated by the supernova we obtain an upper limit on the leptonic photon coupling constants, $\alpha_{l} < 5.4 \times 10^{-11}$. Under certain assumptions about $\gamma_{l}$ - trapping conditions we find that the region of $\alpha_{l} = 10^{-8} - 10^{-7}$ might be of interest for an experimental search for leptonic photons.
Sterile neutrino decay as a common origin for LSND/MiniBooNe and T2K excess events
S. N. Gninenko
Physics , 2011, DOI: 10.1103/PhysRevD.85.051702
Abstract: 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.
Muon capture rates from precision measurements of the muon disappearance
S. N. Gninenko
Physics , 2013,
Abstract: In a typical experiment the nuclear \mu-capture rate is determined from measurements of the time constant of the muon decay exponential in a target. We propose a new approach for the evaluation of the \mu-capture rate, which is based on direct measurements of the \mu^- disappearance rate in the target. Considering, as an example, the reaction of \mu-capture on proton, we demonstrate that measurements of the \mu^- disappearance at different values of the hydrogen gas pressure in the target could be used to avoid a pressure-dependent correction and determine the "vacuum" \mu p -> \nu n reaction rate with accuracy better than 10^{-2} after extrapolation to zero gas density. The proposed method could be used to perform precision measurements of the \mu^- capture rate on different types of nuclei in one experiment.
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