We determine the neutrino parameters for MSW and vacuum oscillations (active and sterile neutrinos) that are allowed by the separate, and collective, imposition of the constraints from total event rates in the chlorine, GALLEX, SAGE, and SuperKamiokande experiments (504 days), the SuperKamiokande electron energy spectrum, and the SuperKamiokande zenith-angle dependence. The small mixing angle MSW solution is acceptable at the 7% C.L. (8% for sterile nu's) and the vacuum solution is acceptable at the 6% C.L. . The best-fit global MSW solution for active neutrinos is: Delta m^2 = 5 x 10^-6 eV^2, sin^2 (2 theta) = 5.5 x 10^{-3} (and for sterile neutrinos: Delta m^2 = 4 x 10^-6 eV^2, sin^2 (2 theta) = 7 x 10^-3). For vacuum oscillations, the best-fit solution is: Delta m^2 = 6.5 x 10^-11 eV^2, sin^2 (2 theta) = 0.75 . An arbitrary combination of undistorted (no oscillations) pp, 7Be, 8B, and CNO neutrino fluxes is inconsistent with the combined data sets at the 3.5 sigma C.L., independent of astrophysical considerations. We use improved calculations of solar model fluxes, neutrino absorption cross sections and energy spectra, and a detailed evaluation of regeneration effects.Comment: LaTeX file. Added Figure comparing with SuperK spectrum. Predictions for LENS experiment. Viewgraphs and related information at http://www.sns.ias.edu/~jn

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Spectroscopic studies of two beta rays from 100Mo are shown to be of potential interest for investigating both the Majorana nu mass by neutrinoless double beta decay (0nubetabeta) and low energy solar nu's by inverse beta decay. With a multiton 100Mo detector, coincidence studies of correlated betabeta from 0nubetabeta, together with the large Q value ( Q(betabeta)), permit identification of the nu-mass term with a sensitivity of approximately 0.03 eV. Correlation studies of the inverse beta decay and the successive beta decay of 100Tc, together with the large capture rates for low energy solar nu's, make it possible to detect, in real time, individual low energy solar nu in the same detector.

Neutrino oscillation scenarios predict correlations, and zones of avoidance, among measurable quantities such as spectral energy distortions, total fluxes, time dependences, and flavor content. The comparison of observed and predicted correlations will enhance the diagnostic power of solar neutrino experiments. A general test of all presently-allowed (2ν) oscillation solutions is that future measurements must yield values outside the predicted zones of avoidance. To illustrate the discriminatory power of the simultaneous analysis of multiple observables, we map currently allowed regions of ∆m 2 − sin 2 2θ onto planes of quantities measurable with the Sudbury Neutrino Observatory (SNO). We calculate the correlations that are predicted by vacuum and MSW (active and sterile) neutrino oscillation solutions that are globally consistent with all available neutrino data. We derive approximate analytic expressions for the dependence of individual observables and specific correlations upon neutrino oscillations parameters. We also discuss the prospects for identifying the correct oscillation solution using multiple SNO observables.

We calculate accurately the number of solar neutrino events expected as a function of solar zenith angle, with and without neutrino oscillations, for detectors at the locations of Super-Kamiokande, SNO, and the Gran Sasso National Laboratory. Using different earth models to estimate geophysical uncertainties, and different solar models to estimate solar uncertainties, we evaluate distortions predicted by the MSW effect in the zenith angle distributions of solar neutrino events. The distortions are caused by oscillations and by ν − e interactions in the earth that regenerate ν e from ν µ or ν τ . We show that the first two moments of the zenith-angle distribution are more sensitive to the small mixing angle MSW solution than the conventionally studied daynight asymmetry. We present iso-sigma contours that illustrate the potential of Super-Kamiokande, SNO, BOREXINO, ICARUS and HERON/HELLAZ for detecting the earth regeneration effect at their actual locations (and at the equator). MSW solutions favored by the four pioneering solar neutrino experiments predict characteristic distortions for Super-Kamiokande, SNO, BOREXINO, and ICARUS that range from being unmeasurably small to > 5σ (stat) after only a few years of observations. 0

Flavor changing (FC) neutrino-matter interactions can account for the zenith-angle-dependent deficit of atmospheric neutrinos observed in the SuperKamiokande experiment, without directly invoking either neutrino mass or mixing. We find that FC n m -matter interactions provide a good fit to the observed zenith angle distributions, comparable in quality to the neutrino oscillation hypothesis. The required FC interactions arise naturally in many attractive extensions of the standard model. [S0031-9007(99) PACS numbers: 14.60. Pq, 14.60.St, 25.30.Pt, 96.40.Tv Neutrinos produced as decay products in hadronic showers from cosmic ray collisions with nuclei in the upper atmosphere [1] have been observed by several detectors [2][3][4][5][6][7]. Although the absolute fluxes of atmospheric neutrinos are largely uncertain, the expected ratio ͑m͞e͒ of the muon neutrino flux ͑n m 1n m ͒ over the electron neutrino flux ͑n e 1n e ͒ is robust, since it largely cancels out the uncertainties associated with the absolute flux. In fact, this ratio has been calculated [1] with an uncertainty of less than 5% over energies varying from 0.1 to 100 GeV. In this resides our confidence in the longstanding atmospheric neutrino anomaly.Although the first iron-calorimeter detectors in Fréjus [2] and NUSEX [3] reported a value of the double ratio, R͑m͞e͒ ͑m͞e͒ data ͑͞m͞e͒ MC , consistent with one, all of the water Cherenkov detectors, Kamiokande [4], IMB [5], and SuperKamiokande [6], have measured R͑m͞e͒ significantly smaller than one. Moreover, not long ago, the Soudan-2 Collaboration, also using an iron calorimeter, reported a small value of R͑m͞e͒ [7], showing that the so-called atmospheric neutrino anomaly was not a feature of water Cherenkov detectors.Recent SuperKamiokande high statistics observations [6] indicate that the deficit in the total ratio R͑m͞e͒ is due to the number of neutrinos arriving in the detector at large zenith angles. Although e-like events do not present any compelling evidence of a zenith angle dependence, the m-like event rates are substantially suppressed at large zenith angles.The n m ! n t [6,8], as well as the n m ! n s [8,9], oscillation hypothesis provides an appealing explanation for this smaller-than-expected ratio, as they are simple and well motivated theoretically. This led the SuperKamiokande Collaboration to conclude that their data provide good evidence for neutrino oscillations and neutrino masses.In this Letter we give an alternative explanation of the atmospheric neutrino data in terms of flavor changing (FC) neutrino-matter interactions [10][11][12][13][14]. We show that, even if neutrinos have vanishing masses and/or the vacuum mixing angle is negligible, FC neutrino-matter interactions can still explain the SuperKamiokande data.There are attractive theories beyond the standard model (SM), where neutrinos are naturally massless [15] as a result of a protecting symmetry, such as B-L in the case of supersymmetric SU͑5͒ models [16] and the model proposed in [17], or chiral symmetry in theories w...

Individual neutrino fluxes are not well determined by the four operating solar neutrino experiments. Assuming neutrino oscillations occur, the pp electron neutrino flux is uncertain by a factor of 2, the 8 B flux by a factor of 5, and the 7 Be flux by a factor of 45. For matter-enhanced oscillation ͑MSW͒ solutions, the range of allowed differences of squared neutrino masses, ⌬m 2 , varies between 4ϫ10 Ϫ6 eV 2 and 1ϫ10 Ϫ4 eV 2 , while 4ϫ10 Ϫ3 рsin 2 2р1.5ϫ10 Ϫ2 or 0.5рsin 2 2р0.9. For vacuum oscillations, ⌬m 2 varies between 5ϫ10 Ϫ11 eV 2 and 1ϫ10 Ϫ10 eV 2 , while 0.7рsin 2 2р1.0. The inferred ranges of neutrino parameters depend only weakly on which standard solar model is used. Calculations of the expected results of future solar neutrino experiments ͑SuperKamiokande, SNO, BOREXINO, ICARUS, HELLAZ, and HERON͒ are used to illustrate the extent to which these experiments will restrict the range of the allowed neutrino mixing parameters. For example, the double ratio ͑observed ratio divided by standard model ratio͒ of neutral current to charged current event rates to be measured in the SNO experiment varies, at 95% confidence limit, over the range 1.0 ͑no oscillations into active neutrinos͒, 3.1 Ϫ1.3 ϩ1.8 ͑small mixing angle MSW͒, 4.4 Ϫ1.4 ϩ2.0 ͑large mixing angle MSW͒, and 5.2 Ϫ2.9 ϩ5.6 ͑vacuum oscillations͒. We present an improved formulation of the ''luminosity constraint'' and show that at 95% confidence limit, this constraint establishes the best available limits on the rate of creation of pp neutrinos in the solar interior and provides the best upper limit to the 7 Be neutrino flux. The actual rate of creation of solar neutrinos in the solar interior to the rate predicted by the standard solar model can vary ͑while holding the CNO neutrino flux constant͒ between 0.55 and 1.08 for pp neutrinos and between 0.0 and 6.35 for 7 Be neutrinos.

We study the stability of the two-neutrino vacuum oscillation solution of the solar neutrino problem with respect to changes of the total fluxes of 8 B and 7 Be neutrinos, Φ B and Φ Be . For any value of Φ Be from the interval 0.7Φ BP Be ≤ Φ Be ≤ 1.3Φ BP Be the solar ν e oscillations into an active neutrino, ν e ↔ ν µ(τ ) , provide at 95% C.L. a description of the existing solar neutrino data forBe being the fluxes in the solar model of Bahcall-Pinsonneault from 1992. For Φ Be ∼ = (0.7 − 1.3)Φ BP Be we find also at 95% C.L. two new (one new) ν e ↔ ν µ(τ ) (ν e ↔ ν s ) oscillation solutions: i) for Φ B ∼ = (0.35 − 0.43)Φ BP B at ∆m 2 ∼ = (4.7 − 6.5) × 10 −12 eV 2 ((4.8 − 6.4) × 10 −12 eV 2 ) and sin 2 2θ ∼ > 0.71 (0.74), and ii) for Φ B ∼ = (0.45 − 0.65)Φ BP B at ∆m 2 ∼ = (3.2 − 4.0) × 10 −11 eV 2 and sin 2 2θ ∼ > 0.59. The physical implications of the new solutions for the future solar neutrino experiments are discussed. The data rule out at 97% -98% (99 %) C.L. the possibility of a universal (neutrino energy independent) suppression of the different components of the solar neutrino flux, resulting from solar ν e oscillations or transitions into active (sterile) neutrino.