D.H. Perkins

Tri-bimaximal mixing and the neutrino oscillation data

Abstract Following recent results from the SNO solar neutrino experiment and the K2K long-baseline neutrino experiment, the combined existing data on neutrino oscillations now point strongly to a specific form for the lepton mixing matrix, with effective bimaximal mixing of ν μ and ν τ at the atmospheric scale and effective trimaximal mixing for ν e with ν μ and ν τ at the solar scale (hence ‘tri-bimaximal’ mixing). We give simple mass-matrices leading to tri-bimaximal mixing, and discuss its relation to the Fritzsch–Xing democratic ansatz.

Measurement of the atmospheric neutrino flavour composition in Soudan 2

Abstract The atmospheric neutrino flavour ratio measured using a 1.52 kton-year exposure of Soudan 2 is found to be 0.72 ± 0.19−0.07+0.05 relative to the expected value from a Monte Carlo calculation. The possible background of interactions of neutrons and photons produced in muon interactions in the rock surrounding the detector has been investigated and is shown not to produce low values of the ratio.

A redetermination of the neutrino mass-squared difference in tri-maximal mixing with terrestrial matter effects

Abstract We re-fit for the neutrino mass-squared difference Δm2 in the threefold maximal (i.e. tri-maximal) mixing scenario using recent CHOOZ and SUPER-K data, taking account of matter effects in the Earth. While matter effects have little influence on reactor experiments and proposed long-baseline accelerator experiments with L ≲ 1000 km, they are highly significant for atmospheric experiments, suppressing naturally νe mixing and enhancing νμ−ντ mixing, so as to effectively remove the experimental distinction between threefold maximal and twofold maximal νμ−ντ mixing. Threefold maximal mixing is fully consistent with the CHOOZ and SUPER-K data and the best-fit value for the neutrino mass-squared difference is Δm2≃(0.98±0.300.23)×10−3 eV2.

Threefold maximal lepton mixing and the solar and atmospheric neutrino deficits

Threefold maximal mixing would imply a cyclic permutation symmetry among the generations. The data from solar and atmospheric neutrino experiments are consistent with such mixing, and require a hierarchical spectrum of mass-squared differences for the neutrinos. A fit for the two independent mass-squared differences (excluding only the HOMESTAKE solar neutrino result) yields: Δm2 = (0.72±0.18) × 10−2 eV2 and Δm′2 < 0.9 × 10−11 eV2 at 90% confidence. In the case that the neutrino mass spectrum is qualitatively similar to that of the charged leptons and quarks, these results can be re-expressed in terms of the neutrino masses as follows: m3 ⋍ 85 ± 10 meV, and m1,m2 < 3 μeV at 90% confidence. Implications for future experiments are discussed.

Multiplicity distributions in neutrino-hydrogen interactions

Abstract Multiplicity distributions of charged hadrons produced in νp interactions are studied using a sample of 7850 charged current interactions in BEBC. Multiplicity moments are studied as functions of the invariant mass of the hadronic system, W , and a comparison is made with other lepton- and hadron-induced reactions. The mean charged multiplicity 〈 n ch 〉 is found to increase linearly with ln W 2 . The other multiplicity moments indicate a close similarity between the neutrino scattering and the class of annihilation processes. A study of the multiplicity distributions in the forward and backward directions in the hadronic c.m.s. gives results in qualitative agreement with the quark parton model.

Further observations on scaling in neutrino interactions

Abstract Analysis of bubble chamber neutrino events indicates that the Bjorken scaling formula applies in the low energy region if the cross-sections are expressed in terms of the Bloom-Gilman parameter x′ = q2/(2Mv + M2). The value of ∫F2dx′ averaged over neutrons and protons, is compatible with the electron data, CVC and pure V, A coupling for the nucleon constituents, provided isoscalar contributions are small. Limits are placed on the relative magnitudes of F1, F2 and F3.

High-energy Electronic Neutrino (

Abstract The total cross-sections for v e ( v e ) -nucleon scattering have been measured. A test has been made of the muon number conservation law. A limit of 2.4 GeV is found the mass of the “Georgi-Glashow type” heavy lepton

\nu_e

Abstract Exposures of the Ne/H 2 filled Big European Bubble Chamber (BEBC) to a dichromatic neutrino (antineutrino) beam produced by 400 GeV protons of the CERN SPS yielded ∼ 3100 events with a negative, and ∼ 1100 with a positive, muon. The neutrino flux is determined from the muon flux in the shielding. Assuming a linear energy dependence of the cross section, the values σ E between 20 and 200 GeV are found to be 0.657 ± 0.012 (stat.) ± 0.027 (syst.) and 0.309 ± 0.009 (stat.) ± 0.013 (syst.) cm 2 (GeV nucleon) −1 , for neutrinos and antineutrinos, respectively. The scaling variable q 2 E decreases significantly with increasing energy both for neutrinos and antineutrinos.

) and Anti-neutrino (

Abstract The phenomenological case for threefold maximal lepton mixing is strengthened by more detailed comparison with existing data. The atmospheric neutrino data are self-consistent and in good agreement with the threefold maximal mixing prediction R = 2 3 ( χ 2 DOF = 4.3 5 , CL = 51%). Including partially-contained event data, the zenith angle dependence also points to threefold maximal mixing, ruling out a range of mixing schemes, including that of Fritzsch and Xing. Accounting for de facto uncertainties in solar neutrino fluxes, the solar neutrino data (including HOMESTAKE) are shown to be consistent with threefold maximal mixing ( χ 2 DOF = 5.1 3 , CL = 16%), as is the upper limit from the LSND appearance experiment. Detailed predictions for forthcoming long-base-line reactor and accelerator experiments are presented.

\bar{\nu}_e

SOUDAN 2 is a 960-ton tracking calorimeter which has been constructed to search for nucleon decay and other phenomena. The full detector consists of 224 calorimeter modules each weighing 4.3 tons. The design and construction of the modules are described. The modules consist of finely segmented iron instrumented with 1 m long drift tubes of 15 mm internal diameter. The tubes enable three spatial coordinates and dE/dx to be recorded for charged particles traversing the tubes.