Physics potentials of pp and pep solar neutrino fluxes

Experimental determinations of the pp and pep fluxes have great potentialities. We briefly review the reasons that make such measurements privileged tests of neutrino properties. We discuss the predictions for these fluxes given by four good solutions to the solar neutrino problem: small- and large-angle MSW and Just-So oscillations into active neutrinos, and small-angle MSW oscillations into sterile neutrinos. In addition, we examine the impact of the planned Hellaz detector, which should measure separately the nu_e and nu_mu fluxes in the pp energy window and the signal from the pep neutrinos, for distinguishing among the different solutions and for determining the solar central temperature.Comment: 14 pages, ReVTeX, plus 9 postscript figure

Testing maximal electron and muon neutrino oscillations with sub-GeV SuperKamiokande atmospheric neutrino data

Motivated by the Exact Parity Model and other theories, the hypothesis that each of the known neutrinos oscillates maximally with a sterile partner has been put forward as an explanation of the atmospheric and solar neutrino anomalies. We provide detailed predictions for muon and electron flux ratios induced in the Kamiokande and SuperKamiokande detectors by sub-GeV atmospheric neutrinos. Several different, carefully chosen cuts on momentum and zenith angle are proposed, emphasizing the role of up-down flux asymmetries.Comment: LaTeX, 8 figures, 17 pages, version to appear in Phys. Rev. D Rapid Communication

Just So? Vacuum Oscillations and MSW: An Update

We find that vacuum oscillations (VO), large-mixing-angle and small-mixing-angle MSW solutions to the solar neutrino problem (SNP) give all very good fits to the most recent results. Measurements of the $^7$Be flux can, in some cases, discriminate between different solutions to the SNP; in particular, VO allow $^7$Be fluxes almost as large as the one predicted by the SSM. We find that no evidence for seasonal variations can be extracted from present data, but that the large statistics of SuperKamiokande should make possible to study a significant portion of the presently allowed parameter space by just looking for seasonal variations. We also discuss the Borexino potential for detecting seasonal variations, which looks really impressive.Comment: 21 pages, ReVTeX, 15 figures as uuencoded compressed postscript files. The postscript file with the text and 14 figures (no figure 4) is available at ftp://risc0.ca.infn.it/pub/private/lissia/infncath9512.ps . To appear in Astroparticle Physic

How Well Do We (and Will We) Know Solar Neutrino Fluxes and Oscillation Parameters?

Assuming neutrino oscillations occur, the pp electron neutrino flux is uncertain by at least a factor of two, the ${\rm ^8B}$ flux by a factor of five, and the ${\rm ^7Be}$ flux by a factor of forty-five. Calculations of the expected results of future solar neutrino experiments (SuperKamiokande, SNO, BOREXINO, ICARUS, HELLAZ, and HERON) are used to illustrate the extent to which these experiments will restrict the range of the allowed neutrino mixing parameters. 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 ${\rm ^7Be}$ neutrino flux.Comment: 37 pages, uuencoded Z-compressed postscript file (with figures); Submitted to Physical Review

Testing solar neutrino MSW oscillations at low delta m^2 through time variations of event rates in GNO and BOREXINO

The Mikheyev-Smirnov-Wolfenstein (MSW) explanation of the solar neutrino problem is currently compatible with three distinct regions of the two-neutrino oscillation parameter space (delta m^2,sin^2 2theta). We focus on the region with the lowest value of delta m^2 (~10^{-7} eV^2), which implies significant Earth regeneration effects for low-energy solar neutrinos. We point out that such effects are not only observable as day-night variations of neutrino event rates in the real-time BOREXINO experiment, but also as seasonal variations in the radiochemical Gallium Neutrino Observatory (GNO) at Gran Sasso. We present detailed calculations of the difference between winter and summer rates in GNO (six months averages) in excess of the trivial seasonal variation due to the Earth orbital eccentricity. We show that, within the low-delta m^2 MSW solution, the net winter-summer GNO rate difference amounts to 4-6 SNU, with a dominant contribution from pp neutrinos. We also give analytical expressions for the winter and summer solar exposure functions at the Gran Sasso site.Comment: 12 pages (RevTeX) + 5 figures (PostScript

Accelerator, reactor, solar and atmospheric neutrino oscillation: beyond three generations

We perform a phenomenological analysis of neutrino oscillation in a four generation framework introducing an additional sterile neutrino. In such a scenario, more than one pattern is possible that can accommodate three hieararchically different mass squared differences as required by the present experiments. We considered two different spectrums. Choosing the ${\Delta{m}}^2$s in the ranges suitable for the LSND, atmospheric and solar neutrino oscillation, limits on the mixing angles are derived, consistent with the most restrictive accelerator and reactor data as well as the atmospheric and solar neutrino results. The allowed mixing angles are found to be constrained very severely in both cases. For one mass pattern in the combined allowed zone the atmospheric anomaly can be explained by $\nu_e - \nu_{\mu}$ oscillation whereas for the other the $\nu_{\mu} - \nu_{\tau}$ channel is preferred. The accelerator experiments CHORUS and NOMAD have different sensitivities in these regions and they can distinguish between the two choices.Comment: Latex, 26 pages, 6 figures, 1 included in the Latex File, remaining 5 available on reques

Where do we stand with solar neutrino oscillations?

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

Intermediate Energy Solar Neutrinos

Intermediate Energy Solar Neutrino