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S. N. Gninenko

Publications and source records attributed to S. N. Gninenko.

85 records · Page 5Linked to original sources
arXiv2002

Search for an exotic three-body decay of orthopositronium

We report on a direct search for a three-body decay of the orthopositronium into a photon and two penetrating particles, o-Ps -> gamma + X1 + X2. The existence of this decay could explain the discrepancy between the measured and the predicted values of the orthopositronium decay rate. From the analysis of the collected data a single candidate event is found, consistent with the expected background. This allows to set an upper limit on the branching ratio < 4.4 \times 10^{-5} (at the 90% confidence level), for the photon energy in the range from 40 keV < E_gamma< 400 keV and for mass values in the kinematical range 0 < mX1+mX2 <900 keV. This result unambiguously excludes the o-Ps -> gamma + X1 + X2 decay mode as the origin of the discrepancy.

hep-ex↗
arXiv2002

Invisible decay of orthopositronium vs extra dimensions

In models of Randall-Sundrum type orthopositronium (o-Ps) can disappear due to tunnelling into additional dimension(s). The experimental signature of this effect is the invisible decay of orthopositronium. We point out that this process may occur at a rate within two or three orders of magnitude of the present experimental upper limit. We discuss this in details and stress that the existence of invisible decay of orthopositronium in vacuum could explain the o-Ps decay rate puzzle. Thus, our result enhances the existing motivation and justifies efforts for a more sensitive search for o-Ps->invisible decay in a near future experiment. Possible manifestations of new physics in other rare (exotic) decays of orthopositronium are also discussed.

hep-ph↗
arXiv2001

Probing lepton flavour violation in $ν_μ + N \to τ+ ...$ scattering and $μ\to tau$ conversion on nucleons

We study lepton flavour-violating interactions which could result in the $τ$-lepton production in the $ν_μN$ scattering or in $μ\to τ$ conversion on nucleons at high energies. Phenomenological bounds on the strength of $\barτν_μ\bar{q}q^{'}$ interactions are extracted from the combined result of the NOMAD and CHORUS experiments on searching for $ν_μ - ν_τ$ oscillations. Some of these bounds supersede limits from rare decays. We also propose a ``missing energy'' type experiment searching for $μ- τ$ conversion on nucleons. The experiment can be performed at a present accelerator or at a future neutrino factory.

hep-ph↗
arXiv2001

The muon anomalous magnetic moment and a new light gauge boson

It is shown that the 2.6 $σ$ discrepancy between the predicted and recently measured value of the anomalous magnetic moment of positive muons could be explained by the existence of a new light gauge boson X with a mass $M_X \leq O(5) GeV$. Phenomenological bounds on the X coupling are discussed.

hep-ph↗
arXiv2000

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

Combined results on $ν_μ\to ν_τ$ oscillations and $νe$-scattering from the Super-Kamiokande and LAMPF experiments, respectively, limit the Dirac $ν_τ$ diagonal magnetic moment to $μ_{ν_τ} < 1.9\times 10^{-9} μ_{B}$. For the scheme with 3 Majorana neutrinos the LAMPF results allow the limitation of effective $ν_τ$ magnetic moment to $μ_{ν_τ} < 7.6 \times 10^{-10}μ_{B}$. The moments in the scheme with additional Majorana light sterile neutrinos as well as experiments on stimulated radiative neutrino conversion are also discussed.

hep-ph↗
arXiv1999

Bound on the tau neutrino magnetic moment from the Super-Kamiokande data

It is shown that recent results from the Super-Kamiokande detector constrain the tau neutrino diagonal magnetic moment to $μ_{ν_τ} < 1.3\times 10^{-7} μ_{B}$ for the case of $ν_μ\to ν_τ$ 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.

hep-ph↗
arXiv1999

Limits on the magnetic moment of sterile neutrino and two-photon neutrino decay

It is shown that the non-zero transition magnetic moment ($μ_{tran}$) between the sterile neutrino ($ν_{s}$) and the muon neutrino ($ν_μ$) could be effectively searched for via the Primakoff effect, in the process of $ν_μ Z \to ν_{s}Z$ conversion in the external Coulomb field of a nucleus $Z$, with the subsequent $ν_{s}\to ν_μ + γ$ decay. From the recent results of the NOMAD neutrino detector at CERN a model-independent constraint of $μ_{tran} < (10^{-6} - 10^{-9}) μ_{B}$ is obtained depending on the value of $ν_{s}$ mass. For the $m_{s}\sim O(1) GeV$ region these bounds are comparable with the present experimental ones on $ν_μ$ and $ν_{e}$ diagonal magnetic moments and are more sensitive than those on $ν_τ$ magnetic moment. From the same analysis the constraint on $ν_τ(ν_{s})\to ν_μ +γ+ γ$ decay lifetime $τ> 2\times10^{13} sec/m_ν^{7}(MeV)$ is obtained. The limit is valid for neutrino masses up to $m_ν\sim O(1)GeV$.

hep-ph↗
arXiv1998

Exotic muon decays and the KARMEN anomaly

An anomaly in time distribution of neutrinos from the ISIS pulsed beam stop source observed by the KARMEN collaboration is discussed. We show that the anomaly can be interpreted as a superposition of two exponentials, both having time constants consistent with the $μ^{+}$ lifetime of 2.2 $μs$. % and, therefore, It is assumed that they both originate from muon decays at rest. One of them describes the time distribution of the prompt neutrino events, while the other describes the time distribution of events from delayed decays of slowly moving ($β\simeq 0.02$) particles in the KARMEN calorimeter. We propose here that these particles are produced in exotic decays of positive muons $μ^{+}\to e^{+} + X$, resulting in the second exponential time distribution shifted by the time of flight with respect to the time distribution of neutrino events. This model gives an aceptable fit to the KARMEN data if $X$ has a mass of 103.9 MeV. The possible decay modes of this new massive neutral particle are discussed. This hypothesis can be experimentally tested in the near future by studying the low energy part of the $e^{+}$ spectrum in the $μ^{+}$ decays.

hep-ph↗
arXiv1998

On mixing angles and magnetic moment of heavy tau neutrino

If the magnetic moment of unstable tau neutrinos with the mass of $O$(MeV) is in the region of $10^{-8}μ_{B} \lesssim μ_{ν_τ} \lesssim 10^{-6}μ_{B}$, it is compatible with the present experimental and cosmological bounds. It is pointed out here, that if the tau neutrino has such a large magnetic moment and can oscillate into a neutrino of another flavour the results from $νe$ scattering experiment at LAMPF constrain the tau neutrino mixing angles to $sin^{2}2θ_{e τ} \lesssim 2\times 10^{-6} - 2\times 10^{-2}$ and $sin^{2}2θ_{μτ} \lesssim 10^{-6} - 10^{-2}$ depending on the magnetic moment value in the allowed region.

hep-ph↗
arXiv1998

Limits on $ν_μ(ν_{e}) \to ν_τ$ 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 $ν_μ(ν_{e}) \to ν_τ$ 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 $sin^{2}2θ_{μτ}\times μ_{ν_τ}^{2} < 1.1 \times 10^{-18}μ_{B}^{2}$ and $sin^{2}2θ_{eτ}\times μ_{ν_τ}^{2} < 2.3 \times 10^{-18}μ_{B}^{2}$ for $Δm^{2} > 10~ eV^{2}$ are presented based on results of a study of the neutrino-electron elastic scattering at LAMPF. For $ν_μ\to ν_τ$ oscillations, this would results in sensitive limit of $sin^{2}2θ_{μτ} < 4 \times 10^{-6}$, assuming the tau neutrino magnetic moment being equal to the present experimental limit of $5.4 \times 10^{-7} μ_{B}$. The tau neutrino magnetic moment would be constrained to $μ_{ν_τ} < 1.0 \times 10^{-8} μ_{B}$, assuming the existence of $ν_μ\to ν_τ$ oscillations with the mixing angle $sin^{2}2θ_{μτ}$ equal to the present experimental limit of 0.01 for $Δm^{2} > 10~ eV^{2}$.\ Under similar assumptions the corresponding limits for $ν_{e}\to ν_τ$ oscillations could be set to $sin^{2}2θ_{eτ} < 8 \times 10^{-6}$ and $μ_{ν_τ} < 3.9 \times 10^{-9}μ_{B}$.

hep-ph↗
arXiv1998

On search for a new light gauge boson from $π^{0}(η)\toγ+ X$ decays in neutrino experiments

It is shown that a new light gauge boson $X$ which might be produced in the decays of pseudoscalar mesons $π^{0}(η)\toγ+ X$ could be effectively searched for in neutrino experiments via the Primakoff effect, in the process of $X + Z\to π^{0}(η) + Z$ conversion in the external Coulomb field of a nucleus. An estimate of the $X\to π^{0}$ conversion rate for the NOMAD neutrino detector at CERN is given.

hep-ph↗
arXiv1997

Limits on leptonic photon interactions from SN1987a

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 $ν\barν\toγ_{l}γ_{l}$. 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, $α_{l} < 5.4 \times 10^{-11}$. Under certain assumptions about $γ_{l}$ - trapping conditions we find that the region of $α_{l} = 10^{-8} - 10^{-7}$ might be of interest for an experimental search for leptonic photons.

hep-ph↗