Direct search for the neutrino mass in the beta decay of tritium: Status of the “Troitsk ν-mass” experiment

The results of the “Troitsk ν-mass” experiment on the search for the neutrino rest mass in tritium beta decay are presented. The investigation of the time dependence of the anomalous, bumplike structure at the end of the beta spectrum, reported earlier, gives an indication of the periodic shift of its position with respect to the endpoint with a period of 0.5 yr. An upper limit on the electron-antineutrino rest mass (m _ν<2.5eV/c ²) is derived after taking the bump into account.     

Bound-state beta-decay and kinematic search for neutrino mass

A new method involving Doppler spectroscopy with laser techniques is proposed to observe bound-state β-decay of tritium. This process, although theoretically expected to occur, has not yet been observed. The proposed method is, in principle, capable of exposing a finite mass of the neutrino. The low source temperatures and laser spectroscopic resolution necessary for a neutrino mass measurement, although extremely difficult to achieve, appear accessible with conceivable advances of these techniques. The underlying discussions and the writing of a first draft of this paper took place in 1982 during an exciting two-week stay of Solly Cohen at AT&T Bell Laboratories. His enthusiasm for fundamental physics and innovative experimentation encouraged discussions on many interesting problems, of which the present subject and paper are representative. This is the last physics paper bearing Solly's name. It is perhaps fitting that, in this work, Solly returned to the subject of bound-state β-decay on which he wrote one of his first papers, thirty years earlier in 1951. We miss Solly as a wise colleague, teacher and friend. Deceased.     

Experiment for search for sterile neutrino at SM-3 reactor

In connection with the question of possible existence of sterile neutrino the laboratory on the basis of SM-3 reactor was created to search for oscillations of reactor antineutrino. A prototype of a neutrino detector with scintillator volume of 400 l can be moved at the distance of 6–11 m from the reactor core. The measurements of background conditions have been made. It is shown that the main experimental problem is associated with cosmic radiation background. Test measurements of dependence of a reactor antineutrino flux on the distance from a reactor core have been made. The prospects of search for oscillations of reactor antineutrino at short distances are discussed.     

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 _νh${\nu }_h$ produced in _νμ${\nu }_{\mu }$ neutral-current-like neutrino interactions. If the _νh${\nu }_h$ exist, it would be also produced by the _νμ${\nu }_{\mu }$ beam from the CERN SPS in the neutrino beam line shielding. The _νh${\nu }_h$?s would penetrate the shielding and be observed through the _νh→γν${\nu }_h\to \gamma \nu$ decay followed by the photon conversion into e⁺e⁻$e^{+}{e}^{-}$ pair in the active target of the NOMAD detector. The _νh${\nu }_h$?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 _νh${\nu }_h$?s we set new constraints on _νh${\nu }_h$ properties and exclude part of the LSND/MiniBooNE _νh${\nu }_h$ 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 _νh${\nu }_h$ in future neutrino experiments.     

Precision measurements and tau neutrino physics in a future accelerator neutrino experiment

We investigate prospects of building a future accelerator-based neutrino oscillation experiment in China, including site selection, beam optimization and tau neutrino physics aspects. CP violation, non-unitary mixing and non-standard neutrino interactions are discussed. We simulate neutrino beam setups based on muon and beta decay techniques and compare Chinese laboratory sites by their expected sensitivities. A case study on the Super Proton–Proton Collider and the China JinPing Laboratory is also presented. It is shown that the muon-decay-based beam setup can measure the Dirac CP phase by about 14.2° precision at 1σ CL, whereas non-unitarity can be probed down to ∣α_ij∣ ≲ 0.37 (i ≠ j = 1, 2, 3) and non-standard interactions to $| {epsilon }_{{ell }{ell }^{prime} }^{m}| lesssim $ 0.11 (${ell }ne {ell }^{prime} =e$, μ, τ) at 90% CL, respectively.     

追寻惰性中微子

冰立方(IceCube) 探测器没有发现惰性中微子存在的证据,严格限制了新一类中微子可能的质量范围。
中微子只通过轻微的弱力和引力跟物质作用,但它们却在不同尺度上起关键作用。它们影响早期宇宙的形成,涉及大爆炸后不久重子的起源,也跟恒星内部的核合成有关,包括恒星死亡时的超新星爆发。其实中微子无处不在：因钾同位素(40K)衰变,一根香蕉每天就释放上百万个中微子。     

Constraining neutrino superluminality from searches for sterile neutrino decays

Superluminal neutrinos are expected to lose energy due to bremsstrahlung. It is dominated by e⁺e⁻$e^{+}{e}^{-}$-pair production if kinematically allowed. The same signature was used in searches for 3-body decays of hypothetical heavy sterile neutrinos. From the published analyses of these searches performed by CERN PS191 and CHARM experiments we set upper limits on the neutrino velocity in the energy range from 0.2 GeV to 280 GeV. Our limits are well below the neutrino velocity favored by the recent OPERA results. For energy-independent neutrino velocity the limits obtained in this Letter are stronger than those coming from ICARUS experiment and observations of Supernova SN1987a.     

Gemma experiment: Three years of the search for the neutrino magnetic moment

The result of the 3-year neutrino magnetic moment measurement at the Kalinin Nuclear Power Plant (KNPP) with the GEMMA spectrometer is presented. Antineutrino-electron scattering is investigated. A high-purity germanium detector of 1.5 kg placed at a distance of 13.9 m from the 3 GW_th reactor core is exposed to the antineutrino flux of 2.7 × 10¹³ cm⁻² s⁻¹. The scattered electron spectra taken in (5184 + 6798) and (1853 + 1021) h for the reactor ON and OFF periods are compared. The upper limit for the neutrino magnetic moment μ_v < 3.2 × 10⁻¹¹μ _B at 90% CL is derived from the data processing.     

Strange particle production and charmed particle search in the gargamelle neutrino experiment

Data is given for single and multiple strange particle production in neutrino reactions in both charged and neutral current channels. A total of 15000 neutrino and antineutrino events has been examined for possible evidence of semi-leptonic decay of a charmed particle. One candidate has been observed. Upper limits on charmed particle production cross-sections are given as a function of the neutrino energy and the invariant mass of the final state hadrons.     

Investigation of space-charge effects in gaseous tritium as a source of distortions of the beta spectrum observed in the Troitsk neutrino-mass experiment

Results of searches for effects of space-charge accumulation in the gaseous tritium source in the Troitsk neutrino-mass experiment are presented. The broadening and the shift of the L3 line of conversion electrons in a ^83m Kr gaseous source circulating together with tritium was investigated. The attained limit on the magnitude of fluctuations of the space-charge potential makes it possible to set a limit on the negative neutrino mass squared in the Troitsk neutrino-mass experiment (?0.8 < Δ m _ν ² ≤ 0 eV²), a spurious effect associated with this potential. A statistically reliable shift of the position of the L3 line is discovered. This indicates that processes of of space-charge accumulation do indeed proceed in the source at a level that is significant for the future experiment Katrin.     

First result for the neutrino magnetic moment from measurements with the GEMMA spectrometer

The first result obtained in the measurements of the neutrino magnetic moment at the Kalinin nuclear power plant with the GEMMA spectrometer is presented. A high-purity germanium detector of mass 1.5 kg placed at a distance of 13.9 m from the reactor core is used in the spectrometer. The antineutrino flux at the detector position is 2.73 × 10¹³ $ \bar \nu The first result obtained in the measurements of the neutrino magnetic moment at the Kalinin nuclear power plant with the GEMMA spectrometer is presented. A high-purity germanium detector of mass 1.5 kg placed at a distance of 13.9 m from the reactor core is used in the spectrometer. The antineutrino flux at the detector position is 2.73 × 10¹³ /(cm² s). The differential method is used to select events of electromagnetic antineutrino-electron scattering. The spectra taken in the reactor-on and reactor-off modes over 6200 and 2064 h, respectively, are compared. On the basis of a data analysis, an upper limit of 5.8 × 10⁻¹¹ μB was set on the neutrino magnetic moment μ _ν at a 90% C.L. Original Russian Text ? A.G. Beda, V.B. Brudanin, E.V. Demidova, C.Vylov, M.G. Gavrilov, V.G. Egorov, A.S. Starostin, M.V. Shirchenko, 2007, published in Yadernaya Fizika, 2007, Vol. 70, No. 11, pp. 1925–1935.     

Segmented HPGe detectors for the search of neutrinoless double beta-decay

Neutrinoless double beta-decay (0vbb-decay) is the most promising approach to distinguish between the possibilities of a Dirac or a Majorana nature of neutrinos. Additionally, a measurement of the half-life of 0vbb-decay can give information on the absolute mass scale of neutrinos. At the moment HPGe detectors yield the most sensitive limits on this Lepton-number violating process. The segmentation of HPGe detectors increases the experimental sensitivity by allowing the reconstruction of event topologies. The successful operation of prototype detectors submerged in cryoliquid demonstrates the viability of this experimental approach.     

Experimental determination of the difference of the beta-decay constants for atomic and molecular tritium

The results of an experiment measuring the difference Δλ=λ_a−λ _m of the beta-decay constants of atomic and molecular tritium are reported. The difference Δλ is determined by comparing the rates of growth of the relative content of radiogenic helium-3 in samples containing atomic and molecular tritium. The result Δλ=(4.6±0.8)×10⁻¹²s⁻¹ corresponds to a relative change of the decay constant by ∼0.26%. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 3, 167–170 (10 August 1998)     

A search for heavy neutrino decays in a neutrino beam

A search has been made for the decays of heavy (≈200–500 MeV/c²) neutrinos, ν_H→νμe, in a 23 m long detector, in the wide-band neutrino beam at the Brookhaven AGS. No significant excess of such events was found and limits are set on the neutrino mixing matrix elements, |U_eH|² and |U_μH|². Results of a more general search for anomalous μe events are also reported.     

A search for neutrino oscillations

We present here the final results of experiments searching for neutrino oscillations, carried out by the CHARM Collaboration. The data — taking took place in 1983. The first experiment was performed by exposing two detectors simultaneously to the CERN PS low energyv _µ beam. In the second experiment the full CHARM detector was exposed to the wide-band horn-focusedv _µ beam of the CERN SPS. Complete details of the experiments and data reduction are presented. No statistically significant signals for neutrino oscillations were observed. Our 90% CL limits in the appearance experiment (v _µ→v _e ) exclude Δm ²≧0.19 eV² for complete mixing (sin²2θ=1), and sin²2θ≧0.008 for the region Δm ²≧30 eV². These results, and the limits observed for (v _µ→v _x ) (disappearance of (v _µ), are in agreement with those of most other experiments but exclude part of the region previously reported as a possible indication ofv _µ→v _e oscillations.     

On the implications of a 17 keV neutrino

We discuss the implications of the recent measurement of a 17 keV mass component in the electron neutrino sector. Such a heavy state must decay in order to be compatible with cosmology; this requires states additional to those of the standard model. The most likely candidates are either majorons, allowing the decay into massless weakly interacting scalars, or single neutrinos, allowing the decay via the Z into light neutrinos. We show that in the latter case there is a lower bound on the lifetime in conflict with the cosmological constraints on this decay channel and on the photon plus neutrino decay channel which is also present. The extensions of the standard model needed to reduce the lifetime are considered. We analyze the mass matrix, playing particular regard to the singlet neutrino case, and discuss how it might be extended to explain the solar neutrino deficit.