Measurement of atmospheric neutrino flux consistent with tau neutrino appearance

A search for the appearance of tau neutrinos from nu(mu) <--> nu(tau) oscillations in the atmospheric neutrinos has been performed using 1489.2 days of atmospheric neutrino data from the Super-Kamiokande-I experiment. A best fit tau neutrino appearance signal of 138+/-48(stat)-32(+15)(syst) events is obtained with an expectation of 78+/-26(syst). The hypothesis of no tau neutrino appearance is disfavored by 2.4 sigma.     

Observation of trimuon events produced in neutrino and antineutrino interactions

We report two trimuon events producedin v interactions. Of these, one is of the charge type ?++, not previously reported. In an antineutrino exposure, one candidate of the charge type +?? has been observed. This type of event has also not been reported previously. The combined π → μ and K → μ background for the three events are calculated to be ～ 0.7 events. The rate relative to charged current events corresponding to these three events is of the order of 4 × 10^?5.     

Observation of muon pairs in neutrino interactions at Serpukhov 70 GeV accelarator

A search for dimuons produced in a spark chamber experiment in neutrino and antineutrino beams of the Serpukhov accelerator is reported. The clear dimuon signal has been observed in vN interactions. R_v = N(2ω)/N(1ω)? (6.2 ± 1.7) × 10^?3 in the energy interval 7.5 ÷ 30 GeV. From antineutrino data we conclude that in the same energy range $\text{R}{}_{\mathrm{<mtext>v</mtext>}}\text{? 1.1. × 10}{}^{\mathrm{?2}}\text{(90\% C.L.)}$.     

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.     

An upper limit on the tau neutrino mass from leptonic tau decays

The partial width of the τ → e ^- v _e v _τ can be calculated from the tau mass, lifetime and branching ratio. The increasing precision on these measurements is making the partial width sensitive to the mass of the tau neutrino. We present the tau neutrino mass dependence on the partial width and show that this leads to a limit of m _r < 71 MeV at the 95% confidence level. We show that the limit is determined by the uncertainty in the tau lifetime and τ → e?v _e v _τ branching ratio. Additional measurements of these values are expected in the next few years and we show that the limit could become competitive with the direct measurements.     

Observation of neutrino-like interactions without muon or electron in the gargamelle neutrino experiment

Events induced by neutral particles and producing hadrons, but no muon or electron, have been observed in the CERN neutrino experiment. These events behave as expected if they arise from neutral current induced processes. The rates relative to the corresponding charged current processes are evaluated.     

Improved limits on the mass of the tau neutrino

Several methods to determine (or set an upper bound on) the mass of the tau neutrino are described. The decay spectrum of \(\tau \to e\bar \nu _e \nu _\tau \) near the high center-of-mass electron-energy end is particularly sensitive to the tau-neutrino mass. It is shown that an upper bound of 20 MeV or lower may be feasible. In addition, improved limits on the mass and mixing angle of a heavy component of the tau-neutrino may be readily obtained. We also discuss the purely leptonic decays of theD andF mesons, and show how measurements of the ratiosB(D→τν_τ/B(D→μν_μ,B(F→τν_τ/B(D→μν_μ can be sensitive to tau-neutrino masses of 30 MeV or greater.     

Mass of tau neutrino in SO(10) GUTs

We investigate the allowed ranges of masses for an unstable tau neutrino in the context of SO(10) GUTs. In light of the new nucleosynthesis results we obtain that there is a narrow window for m_ντ where the LEP, neutrino oscillation and nucleosynthesis data are compatible. This window, which depends on the effective number of neutrinos contributing to nucleosynthesis, has important cosmological consequences and will be tested by ongoing neutrino oscillation and LEP II experiments.     

Study of tau decays to six pions and a neutrino

The tau decays to six-pion final states have been studied with the CLEO detector at the Cornell Electron Storage Ring. The measured branching fractions are B(tau(-)-->2pi(-)pi(+)3pi(0)nu(tau)) = (2.2+/-0.3+/-0.4)x10(-4) and B(tau(-)-->3pi(-)2pi(+)pi(0)nu(tau)) = (1.7+/-0.2+/-0.2)x10(-4). A search for substructure in these decays shows that they are saturated by intermediate states with eta or omega mesons. We present the first observation of the decay tau(-)-->2pi(-)pi(+)omega(nu)tau and the branching fraction is measured to be (1.2+/-0.2+/-0.1)x10(-4). The measured branching fractions are in good agreement with the isospin expectations but somewhat below the conserved-vector-current predictions.     

Simulation of tau neutrino interaction in an emulsion track detector

Simulation of the interactions between tau neutrinos ν_τ and the material of the emulsion track detector using Geant4 software is described. The purpose of the work is to generate artificial events and to estimate, on their basis, the reconstruction accuracy for the geometric parameters (vertex coordinates, impact parameters, and track kink angles) and distributions of these parameters used in the selection criteria of the OPERA experiment.     

An upper limit on the \tau neutrino mass from three- and five-prong tau decays

A bound on the tau neutrino mass is established using the data collected from 1991 to 1995 at with the ALEPH detector. Two separate limits are derived by fitting the distribution of visible energy vs invariant mass in and decays. The two results are combined to obtain a 95% confidence level upper limit of 18.2 MeV/c on the mass of the tau neutrino. Received: 30 October 1997 / Published online: 10 March 1998     

Astrophysical tau neutrinos and their detection by large neutrino telescopes

We present results of the detailed Monte Carlo calculation of the rates of double-bang events in a 1-km³ underwater neutrino telescope taking into account the effects of τ-neutrino propagation through the Earth. As an input, the moderately optimistic theoretical predictions for diffuse neutrino spectra of AGN jets are used.