New physics in solar neutrino experiments?

Solar Neutrinos Before and After Neutrino2004
Author(s): John N. Bahcall, M. C. Gonzalez-Garcia, and Carlos Peña-Garay
Journal: JHEP, 08(2004)016, hep-ph/0406294.

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Abstract: We compare, using a three neutrino analysis, the allowed neutrino oscillation parameters and solar neutrino fluxes determined by the experimental data available Before and After Neutrino 2004. New data available after Neutrino 2004 include refined KamLAND and gallium measurements. We use six different approaches to analyzing the KamLAND data. We present detailed results using all the available neutrino and anti-neutrino data for Delta m^2_{12}, tan^2 theta_{12}, sin^2 theta_{13}, and sin^2 eta (sterile fraction). Using the same complete data sets, we also present Before and After determinations of all the solar neutrino fluxes, which are treated as free parameters, an upper limit to the luminosity fraction associated with CNO neutrinos, and the predicted rate for a 7Be solar neutrino experiment. The 1 sigma (3 sigma) allowed range of Delta m^2_{21} = 8.2^{+0.3}_{-0.3}(^{+{1.0}}_{{-0.8}}) times 10^{-5}, eV2 is decreased by a factor of 1.7 (5), but the allowed ranges of all other neutrino oscillation parameters and neutrino fluxes are not significantly changed. Maximal mixing is disfavored at 5.8 sigma for solar neutrinos. The predicted rate in a 7Be neutrino-electron scattering experiment is 0.665 plus/minus 0.015\, (^{+0.045}_{-0.040}) of the rate implied by the BP04 solar model in the absence of neutrino oscillations. In order to clarify what measurements constrain which parameters best, we also analyze the solar neutrino data separately and the reactor anti-neutrino data separately, both Before and After Neutrino 2004. We derive upper limits to CPT violation in the weak sector by comparing reactor anti-neutrino oscillation parameters with neutrino oscillation parameters. We also show that the recent data disfavor at 91% CL a proposed non-standard interaction description of solar neutrino oscillations.

A Road Map to Solar Neutrino Fluxes, Neutrino Oscillation Parameters, and Tests for New Physics
Author(s): John N. Bahcall and Carlos Peña-Garay
Journal: JHEP 11(2003)004, hep-ph/0305159

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Abstract: We analyze all available solar and related reactor neutrino experiments, as well as simulated future 7Be, p-p, pep, and 8B solar neutrino experiments. We treat all solar neutrino fluxes as free parameters subject to the condition that the total luminosity represented by the neutrinos equals the observed solar luminosity (the `luminosity constraint'). Existing experiments show that the p-p solar neutrino flux is 1.01 ± 0.02 (1 sigma) times the flux predicted by the BP00 standard solar model; the 7Be neutrino flux is 0.97^{+0.28}_{-0.54} the predicted flux; and the 8B flux is 1.01 ± 0.06 the predicted flux. The oscillation parameters are: Delta m2 = 7.3^{+0.4}_{-0.6} × 10-5 eV2 and tan2 theta12 = 0.42^{+0.08}_{-0.06}. We evaluate how accurate future experiments must be to determine more precisely neutrino oscillation parameters and solar neutrino fluxes, and to elucidate the transition from vacuum-dominated to matter-dominated oscillations at low energies. A future 7Be nu-e scattering experiment accurate to ± 10 % can reduce the uncertainty in the experimentally determined 7Be neutrino flux by a factor of four and the uncertainty in the p-p neutrino flux by a factor of 2.5 (to ± 0.8%). A future p-p experiment must be accurate to better than ± 3% to shrink the uncertainty in tan2 theta12 by more than 15%. The idea that the Sun shines because of nuclear fusion reactions can be tested accurately by comparing the observed photon luminosity of the Sun with the luminosity inferred from measurements of solar neutrino fluxes. Based upon quantitative analyses of present and simulated future experiments, we answer the question: Why perform low-energy solar neutrino experiments?

Solar Models and Solar Neutrino Oscillations
Author(s):John N. Bahcall and and Carlos Peña-Garay
Journal: New Journal of Physics 6 (2004) 63, hep-ph/0404061.

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Abstract: We provide a summary of the current knowledge, theoretical and experimental, of solar neutrino fluxes and of the masses and mixing angles that characterize solar neutrino oscillations. We also summarize the principal reasons for doing new solar neutrino experiments and what we think may be learned from the future measurements.

What Can We Learn from Neutrinoless Double Beta Decay Experiments?
Author(s):John N. Bahcall, Hitoshi Murayama, and and C. Peña-Garay
Journal: Phys. Rev. D, 70, 033012 (2004), hep-ph/0403167.

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Abstract: We assess how well next generation neutrinoless double beta decay and normal neutrino beta decay experiments can answer four fundamental questions. 1) If neutrinoless double beta decay searches do not detect a signal, and if the spectrum is known to be inverted hierarchy, can we conclude that neutrinos are Dirac particles? 2) If neutrinoless double beta decay searches are negative and a next generation ordinary beta decay experiment detects the neutrino mass scale, can we conclude that neutrinos are Dirac particles? 3) If neutrinoless double beta decay is observed with a large neutrino mass element, what is the total mass in neutrinos? 4) If neutrinoless double beta decay is observed but next generation beta decay searches for a neutrino mass only set a mass upper limit, can we establish whether the mass hierarchy is normal or inverted? We base our answers on the expected performance of next generation neutrinoless double beta decay experiments and on simulations of the accuracy of calculations of nuclear matrix elements.

Solar Neutrinos Before and After KamLAND
Author(s): John N. Bahcall, M. C. Gonzalez-Garcia, and C. Peña-Garay
Journal: JHEP 02(2003)009, hep-ph/0212147

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Abstract: We use the recently reported KamLAND measurements on oscillations of reactor anti-neutrinos, together with the data of previously reported solar neutrino experiments, to show that: (1) the total 8B neutrino flux emitted by the Sun is 1.00(1.0 \pm 0.06) of the standard solar model (BP00) predicted flux, (2) the KamLAND measurements reduce the area of the globally allowed oscillation regions that must be explored in model fitting by six orders of magnitude in the Delta m^2-tan^2 theta plane, (3) LMA is now the unique oscillation solution to a CL of 4.7sigma, (4) maximal mixing is disfavored at 3.1 sigma, (5) active-sterile admixtures are constrained to sin^2 eta<0.13 at 1 sigma, (6) the observed ^8B flux that is in the form of sterile neutrinos is 0.00^{+0.09}_{-0.00} (1 sigma), of the standard solar model (BP00) predicted flux, and (7) non-standard solar models that were invented to completely avoid solar neutrino oscillations are excluded by KamLAND plus solar at 7.9 sigma . We also refine quantitative predictions for future 7Be and p-p solar neutrino experiments.

Anti-neutrino oscillation parameters regions allowed by KamLAND.

Matter effects in the KamLAND reactor experiment.

After: Solar neutrino oscillations after KamLAND.

    The Sterile-Total flux correlation.

Does the Sun Shine by pp or CNO Fusion Reactions?
Author(s):John N. Bahcall, M. C. gonzalez-Garcia, and Carlos Peña-Garay
Journal: Phys. Rev. Lett., 90, 131301 (2003), astro-ph/0212331

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Abstract: We show that solar neutrino experiments set an upper limit of 7.8% (7.3% including the recent KamLAND measurements) to the amount of energy that the Sun produces via the CNO fusion cycle, which is an order of magnitude improvement upon the previous limit. New experiments are required to detect CNO neutrinos corresponding to the 1.5% of the solar luminosity that the standard solar model predicts is generated by the CNO cycle.

A Solution of the Solar-Neutrino Problem
Author(s):John N. Bahcall and H. A. Bethe
Journal: Phys. Rev. Lett., 65, 2233 (1990)

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Abstract:Comparison of the results from the Kamiokande neutrino-electron scattering experiment with those from the chlorine experiment and with solar models shows that the explanation of the solar-neutrino problem probably requires physics beyond the standard electroweak model with zero neutrino masses. The experimental results, including the shape of the electron-recoil energy spectrum measured by Kamiokande, are in excellent agreement with a nonadiabatic solution of the Mikheyev-Smirnov -Wolfenstein effect, yielding a neutrino mass difference of Δm2 = 1 x 10-8sinΘν eV2.

Before and After: How has the SNO NC measurement changed things?

Author(s): John N. Bahcall, M. C. Gonzalez-Garcia, and C. Peña-Garay
Journal: JHEP, 07(2002)054 (August 6, 2002), hep-ph/0204314

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Abstract: We present "Before and After" global oscillation solutions, as well as predicted "Before and After" values and ranges for ten future solar neutrino observables (for BOREXINO, KamLAND, SNO, and a generic p-p detector). The "Before" case includes all solar neutrino data (and some theoretical improvements) available prior to April 20, 2002 and the "After" case includes, in addition, the new SNO data on the CC, NC, and day-night asymmetry. We have performed global analyses using the full SNO day-night energy spectrum and, alternatively, just the SNO CC and NC rates and the day-night effect. The LMA solution is the only currently allowed MSW oscillation solution at ~ 99% CL. The LOW solution is allowed only at more than 2.5 sigma, SMA is now excluded at 3.7 sigma or 4.7 sigma, depending upon analysis strategy, and pure sterile oscillations at more than 4.7 sigma. Small mixing angles are "out" (pure sterile is "way out"); MSW with large mixing angles is definitely "in." Vacuum oscillations are allowed at 3 sigma, but not at 2 sigma. Precise maximal mixing is excluded at 3.2 sigma for MSW solutions and at more than 2.8 sigma for vacuum solutions. Most of the predicted values for future observables for the BOREXINO, KamLAND, SNO, and p-p future measurements are changed only by minor amounts by the inclusion of the recent SNO data. In order to test the robustness of the allowed oscillation regions that are inferred from the measurements and the predicted values of future solar neutrino obervables, we have used a variety of strategies for analyzing the SNO and other experimental data.

If sterile neutrinos exist, how can one determine the total solar neutrino fluxes?
Author(s): John N. Bahcall, M. C. Gonzalez-Garcia, and C. Peña-Garay
Journal: Phys. Rev. C., 66, 035802 (2002), hep-ph/0204194.

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Abstract: The 8B solar neutrino flux inferred from solar neutrino experiments is within 11% (1 sigma) of the predicted standard solar model value if only active neutrinos exist, but could be as large as 1.7 times the standard prediction if sterile neutrinos exist. We show that the total 8B neutrino flux (active plus sterile neutrinos) can be determined experimentally to about 10% (1 sigma) by combining charged current measurements made with the KamLAND reactor experiment and with the SNO solar neutrino experiment, provided the LMA neutrino oscillation solution is correct and the simulated performance of KamLAND is valid. Including also SNO NC data, the sterile component of the 8B neutrino flux can be measured by this method to an accuracy of about 12% (1 sigma) of the standard solar model flux. Combining Super-Kamiokande and KamLAND measurements and assuming the oscillations occur only among active neutrinos, the 8B neutrino flux can be measured to 6% (1 sigma); the total flux can be measured to an accuracy of about 9%. The total 7Be solar neutrino flux can be determined to an accuracy of about 28% (1 sigma) by combining measurements made with the KamLAND, SNO, and gallium neutrino experiments. One can determine the total 7Be neutrino flux to a 1 sigma accuracy of about 11% or better by comparing data from the KamLAND experiment and the BOREXINO solar neutrino experiment provided both detectors work as expected. The pp neutrino flux can be determined to an accuracy of about 15% using data from the gallium, KamLAND, BOREXINO, and SNO experiments.

How Accurately Can One Test CPT Conservation with Reactor and Solar Neutrino Experiments?
Author(s): John N. Bahcall, V. Barger, and Danny Marfatia
Journal: Phys. Lett. B, 534 (1-4), 120, hep-ph/0201211.

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Abstract: We show that the combined data from solar neutrino experiments and from the KamLAND reactor neutrino experiment can establish an upper limit on, or detect, potential CPT violation in the neutrino sector of order 10-20 GeV to 10-21 GeV.

Robust signatures of solar neutrino oscillation solutions
Author(s): John N. Bahcall, M. C. Gonzalez-Garcia, Carlos Peña-Garay
Journal: JHEP 04(2002)007, hep-ph/0111150.

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Abstract: With the goal of identifying signatures that select specific neutrino oscillation parameters, we test the robustness of global oscillation solutions that fit all the available solar and reactor experimental data. We use three global analysis strategies previously applied by different authors and also determine the sensitivity of the oscillation solutions to the critical nuclear fusion cross section, S17(0), for the production of 8B. The favored solutions are LMA, LOW, and VAC in order of g.o.f. The neutral current to charged current ratio for SNO is predicted to be 3.5 +- 0.6 (1 sigma), which is separated from the no-oscillation value of 1.0 by much more than the expected experimental error. The predicted range of the day-night difference in charged current rates is (8.2 +- 5.2)% and is strongly correlated with the day-night effect for neutrino-electron scattering. A measurement by SNO of either a NC to CC ratio > 3.3 or a day-night difference > 10%, would favor a small region of the currently allowed LMA neutrino parameter space. The global oscillation solutions predict a 7Be neutrino-electron scattering rate in BOREXINO and KamLAND in the range 0.66 +- 0.04 of the BP00 standard solar model rate, a prediction which can be used to test both the solar model and the neutrino oscillation theory. Only the LOW solution predicts a large day-night effect(< 42%) in BOREXINO and KamLAND. For the reactor KamLAND experiment, the LMA solution predicts a charged current rate relative to the standard model of 0.44^{+0.22}_{-0.07} (1 sigma) [0.44^{+0.29}_{-0.17} (3 sigma)], Ethreshold = 1.22 MeV, with a somewhat larger allowed range for a higher energy threshold.

How many sigmas is the solar neutrino effect?
Author(s): John N. Bahcall
Journal: Phys. Rev. C, 65, 015802,hep-ph/0108147 .

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Abstract: The minimal standard electroweak model can be tested by allowing all the solar neutrino fluxes, with undistorted energy spectra, to be free parameters in fitting the measured solar neutrino event rates, subject only to the condition that the total observed luminosity of the sun is produced by nuclear fusion. The rates of the five experiments prior to SNO (chlorine, Kamiokande, SAGE, GALLEX, Super-Kamiokande) cannot be fit by an arbitrary choice of undistorted neutrino fluxes at the level of 2.5 (formally 99% C.L.). Considering just SNO and Super-Kamiokande, the discrepancy is at the 3.3 level (10-3 C.L.). If all six experiments are fit simultaneously, the formal discrepancy increases to 4 (7 x 10-5 C.L.). If the relative scaling in temperature of the nuclear reactions that produce 7Be and 8B neutrinos is taken into account, the formal discrepancy is at the 7.4 level.

The luminosity constraint on solar neutrino fluxes
Author(s): John N. Bahcall
Journal: Phys. Rev. C., 65, 025801, hep-ph/0108148.

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Abstract: A specific linear combination of the total solar neutrino fluxes must equal the measured solar photon luminosity if nuclear fusion reactions among light elements are responsible for solar energy generation. This luminosity constraint, previously used in a limited form in testing the no neutrino oscillation hypothesis, is derived in a generality that includes all of the relevant solar neutrino fluxes and which is suitable for analyzing the results of many different solar neutrino experiments. With or without allowing for neutrino oscillations, the generalized luminosity constraint can be used in future analyses of solar neutrino data. Accurate numerical values for the linear coefficients are provided.

Global Analysis of Solar Neutrino Oscillations Including SNO CC Measurement
Author(s): John N. Bahcall, M. C. Gonzalez-Garcia, and Carlos Peña-Garay
Journal: JHEP 08(2001)014 (August 29, 2001), hep-ph/0106258.

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Abstract: For active and sterile neutrinos, we present the globally allowed solutions for two neutrino oscillations. We include the SNO CC measurement and all other relevant solar neutrino and reactor data. Five active neutrino oscillation solutions (LMA, LOW, SMA, VAC, and Just So2) are currently allowed at 3; three sterile neutrino solutions (Just So2, SMA, and VAC) are allowed at 3. The goodness of fit is satisfactory for all eight solutions. We also investigate the robustness of the allowed solutions by carrying out global analyses with and without: 1) imposing solar model constraints on the 8B neutrino flux, 2) including the Super-Kamiokande spectral energy distribution and day-night data, 3) including a continuous mixture of active and sterile neutrinos, 4) using an enhanced CC cross section for deuterium (due to radiative corrections), and 5) an optimistic, hypothetical reduction by a factor of three of the error of the SNO CC rate. For every analysis strategy used in this paper, the most favored solutions all involve large mixing angles: LMA, LOW, or VAC. The favored solutions are robust, but the existence at 3 of individual sterile solutions and the active Just So2 solution is sensitive to the analysis assumptions.

Why Do Solar Neutrino Experiments Below 1 MeV?
Author(s): John N. Bahcall
Journal: in Low Energy Solar Neutrino Detection, Proceedings of the 2nd International Workshop, eds. Y. Suzuki, M. Nakahata, and S. Moriyama (World Scientific, 2002) [hep-ex/0106086].

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Abstract: I discuss why we need solar neutrino experiments below 1 MeV. I also express my prejudices about the desired number and types of such experiments, emphasizing the importance of p-p solar neutrino experiments.

Solar neutrinos: global analysis and implications for SNO
Author(s): John N. Bahcall, Plamen I. Krastev, and Alexei Yu. Smirnov
Journal: JHEP, 05(2001)015 (June 8, 2001), hep-ph/0103179.

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Abstract: We present a global analysis of all the available solar neutrino data treating consistently the 8B and hep neutrino fluxes as free parameters. The analysis reveals at 99.7% C.L. eight currently-allowed discrete regions in two-neutrino oscillation space, five regions corresponding to active neutrinos and three corresponding to sterile neutrinos. Most of the allowed oscillation solutions are robust with respect to changes in the analysis procedures, but the traditional vacuum solution is fragile. The globally-permitted range of the 8B neutrino flux, 0.45 to 1.95 in units of the BP2000 flux, is comparable to the 3 range allowed by the standard solar model. We discuss the implications for SNO of a low mass, m2 ~ 6 x 10-12 eV2, vacuum oscillation solution, previously found by Raghavan, and by Krastev and Petcov, but absent in recent analyses that included Super-Kamiokande data. For the SNO experiment, we present refined predictions for the charged-current rate and the ratio of the neutral-current rate to charged-current rate. The predicted charged-current rate can be clearly distinguished from the no-oscillation rate only for the LMA solution. The predicted ratio of the neutral-current rate to charged-current rate is distinguishable from the no-oscillation ratio for the LMA, SMA, LOW, and VAC solutions for active neutrinos.

Correlations of Solar Neutrino Observables for SNO
Author(s): John N. Bahcall, Plamen I. Krastev, and Alexei Yu. Smirnov
Journal: Phys. Rev. D, 63, 053012 (March 1, 2001), hep-ph/0006078

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Abstract: 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 (two neutrino) 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 neutrino masses and mixing angles 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.

SNO: Predictions for Ten Measurable Quantities
Author(s): J. N. Bahcall, P. I. Krastev, and A. Yu. Smirnov
Journal: Phys. Rev. D, 62, 093004 (November 1, 2000), hep-ph/0002293

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Abstract: We calculate the range of predicted values for 10 quantities that will be measured by the Sudbury Neutrino Observatory (SNO). We use neutrino oscillation solutions (vacuum and MSW; active and sterile neutrinos) that are globally consistent with all available neutrino data and estimate realistic theoretical and experimental uncertainties. The neutral current to charged current double ratio is predicted to be more than 9 from the no-oscillation solution for all of the currently favored neutrino oscillation solutions. The best-fit oscillation solutions predict a CC day-night rate difference between -0.1% and +12.5% and a NC day-night difference < 0.01%. We present also the predicted range for the first and the second moments of the charged current electron recoil energy spectrum, the charged current, the neutral current, and the -e scattering rates, the seasonal dependence of the charged current rate, and the double ratio of neutrino-electron scattering rate to charged current rate.

What Will the First Year of SNO Show?
Author(s): J. N. Bahcall, P. I. Krastev, and A. Yu. Smirnov
Journal: Phys. Lett. B, 477, 401-409 (March 30, 2000); hep-ph/9911248

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Abstract: The ratio of measured to combined standard model predicted CC events in SNO will be 0.47 if no oscillations occur. The best-fit active oscillation predictions for the CC ratio are: 0.35-0.39 (MSW, active) and 0.38-0.42 (vacuum) (all for a 5 MeV threshold), typically 20% less than the no-oscillation expectation. We calculate the ratios allowed at 99% CL and determine the dependence of the ratios on energy threshold. If the high-energy anomaly observed by SuperKamiokande is due to an enhanced hep flux, MSW active solutions predict that out of a total of 5000 CC events above 5 MeV in SNO between 49 and 54 events will be observed above 13 MeV whereas only 19 events are expected for no-oscillations and a nominal standard hep flux.

Is Large Mixing Angle MSW the Solution of the Solar Neutrino Problems?
Author(s): J. N. Bahcall, P. I. Krastev, and A. Yu. Smirnov
Journal: Physical Review D., 60, 93001-13 (November 1, 1999), hep-ph/9905220

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Abstract: Recent results on solar neutrinos provide hints that the LMA MSW solution could be correct. We perform accurate calculations for potential `smoking-gun' effects of the LMA solution in the SuperKamiokande solar neutrino experiment, including: (1) an almost constant reduction of the standard recoil electron energy spectrum (with a weak, < 10%, relative increase below 6.5 MeV); (2) an integrated difference in day-night rates (2% to 14%); (3) an approximately constant zenith-angle dependence of the nighttime event rate; (4) a new test for the difference in the shape of the equally-normalized day-night energy spectra (~ 1%); and (5) annual variations of the signal due to the regeneration effect (~ 6 times smaller than the integrated day-night effect). We also establish a relation between the integrated day-night asymmetry and the seasonal asymmetry due to LMA regeneration. As a cautionary example, we simulate the effect of an absolute energy calibration error on the shape (distortion) of the recoil energy spectrum. We compare LMA predictions with the available SuperKamiokande data and discuss the possibilities for distinguishing experimentally between LMA and vacuum oscillations. If LMA is correct, global solutions combining data from different types of measurements made by SuperKamiokande or by different solar neutrino experiments could reveal in the next few years a many indication of neutrino oscillations.

Letter from Bruno Pontecorvo in 1972

Pontecorvo remarks with regard to the latest results of the chlorine experiment of Ray Davis: "It starts to be really interesting! It would be nice if all this will end with something unexpected from the point of view of particle physics. Unfortunately, it will not be easy to demonstrate this, even if nature works that way."

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This letter is published in the proceedings of the 23rd Johns Hopkins Workshop on Current Problems in Particle Theory, Neutrinos in the Next Millennium, Baltimore, June 10-12, 1999 (World Scientific, Singapore 2000), pp. 91-112.

Where do we stand with solar neutrino oscillations?
Author(s): J. N. Bahcall, P. I. Krastev, and A. Yu. Smirnov
Journal: Physical Review D, 58, 096016-1 - 096016-22; hep-ph/9807216.

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Abstract: 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 m2 = 5 x 10-6 eV2, sin2 (2 theta) = 5.5 x 10-3 (and for sterile neutrinos: Delta m2 = 4 x 10-6 eV2, sin2 (2 theta) = 7 x 10-3). For vacuum oscillations, the best-fit solution is: Delta m2 = 6.5 x 10-11 eV2, sin2 (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.

Do hep neutrinos affect the solar neutrino energy spectrum?

Author(s): John N. Bahcall, Plamen I. Krastev
Journal: Physics Letters B, 436/3-4, 243-250 (September 24, 1998), hep-ph/9807525

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Abstract: If the low energy cross section for 3He + p--> 4He + e+ + nue, the `hep' reaction, is  >~  20 times larger than the best (but uncertain) theoretical estimates, then this reaction could significantly influence the electron energy spectrum produced by solar neutrino interactions and measured in the SuperKamiokande, SNO, and ICARUS experiments. We compare predicted energy spectra for different assumed hep fluxes and different neutrino oscillation scenarios with the observed SuperKamiokande spectrum. The spectra with enhanced hep contributions provide better fits to the SuperKamiokande data.

Does the Sun Appear Brighter at Night in Neutrinos?
Author(s): J. N. Bahcall and P. I. Krastev
Journal: Physical Review C, 56, 2839-2857 (November 1997); hep-ph/9706239.

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Abstract: 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 -e interactions in the earth that regenerate electron type neutrinos from mu or tau neutrinos. 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 day-night 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 > 5 (stat) after only a few years of observations.

Neutrino Oscillations and Moments of Electron Spectra
Author(s): J. N. Bahcall, P. I. Krastev, and E. Lisi
Journal: Physical Review C, 55, 494-503 (January 1, 1997); nucl-ex/9610010.

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Abstract: We show that the effects of neutrino oscillations on 8B solar neutrinos are described well by the first two moments (the average and the variance) of the energy distribution of scattered or recoil electrons. For the SuperKamiokande and the Sudbury Neutrino Observatory experiments, the differences between the moments calculated with oscillations and the standard, no-oscillation moments are greater than 3 standard deviations for a significant fraction of the neutrino mass-mixing (m2, sin22) parameter space.

Tests of Electron Flavor Conservation with the Sudbury Neutrino Observatory
Author(s): John N. Bahcall and Eligio Lisi
Journal: Physical Review D, 54, 5417-5433 (November 1, 1996); hep-ph/9607433

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Abstract: We analyze tests of electron flavor conservation that can be performed at the Sudbury Neutrino Observatory (SNO). These tests, which utilize 8B solar neutrinos interacting with deuterium, measure: 1) the shape of the recoil electron spectrum in charged-current (CC) interactions (the CC spectrum shape); and 2) the ratio of the number of charged current to neutral current (NC) events (the CC/NC ratio). We determine standard model predictions for the CC spectral shape and for the CC/NC ratio, together with realistic estimates of their errors and the correlations between errors. We consider systematic uncertainties in the standard neutrino spectrum and in the charged-current and neutral current cross-sections, the SNO energy resolution and absolute energy scale, and the SNO detection efficiencies. Assuming that either matter-enhanced or vacuum neutrino oscillations solve the solar neutrino problems, we calculate the confidence levels with which electron flavor non-conservation can be detected using either the CC spectrum shape or the CC/NC ratio, or both. If the SNO detector works as expected, the neutrino oscillation solutions that best-fit the results of the four operating solar neutrino experiments can be distinguished unambiguously from the standard predictions of electron flavor conservation.

What Can Be Learned by Measuring the Fluxes of the 7Be
and the pep Solar Neutrino Lines?
Author(s): J. N. Bahcall and P. I. Krastev
Journal: Physical Review C, 55, 929-941 (February 1, 1997); astro-ph/9607013

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Abstract: Measurements of the interaction rates of the solar neutrino lines of 7Be and pep can be used, independent of solar models, to test whether electron flavor is conserved, to determine survival probabilities of electron-type neutrinos at specific energies, and to test for the existence of sterile neutrinos. We present analytic descriptions of these tests. We also illustrate by numerical simulations, assuming matter-enhanced and vacuum neutrino oscillations, what measurements of solar neutrino lines can teach us about neutrino masses and mixing angles.

Figures are available in one gziped uucompressed file (Lines.uu) via anonymous ftp to in the directory /pub/krastev/Lines.

How Does the Sun Shine?
Author(s): J. N. Bahcall, M. Fukugita, and P. I. Krastev
Journal: Physics Letters B, 374, 1-6 (May 2, 1996); astro-ph/9602065.

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Abstract: The results of the four operating solar neutrino experiments are consistent with the hypothesis that more than 99.9 percent of the solar luminosity is generated by CNO fusion reactions if MSW neutrino oscillations occur.

How Well Do We (and Will We) Know Solar Neutrino Fluxes and Oscillation Parameters?
Author(s): J. N. Bahcall and P. I. Krastev
Journal: Physical Review D, 53, 4211 (April 15, 1996); hep-ph/9512378.

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Abstract: Individual neutrino fluxes are not well determined by the four operating solar neutrino experiments. Assuming neutirno oscillations occur, the pp neutrino flux is uncertain by a factor of two, the boron neutrino flux by a factor of eight, and the berylium neutrino 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 exeriments will restrict the range of allowed neutrino mixing parameters.

Do solar-neutrino experiments imply new physics?
Author(s): J. N. Bahcall and H. A. Bethe
Journal: Physical Review D, 47, 1298 (February 15, 1993); hep-ph/9212204.

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None of the 1000 solar models in a full Monte Carlo simulation is consistent with the results of the chlorine or the Kamiokande experiments. Even if the solar models are forced artifically to have a 8B neutrino flux in agreeement with the Kamiokande experiment, none of the fudged models agrees with the chlorine observations. The GALLEX and SAGE experiments, which currently have large statistical uncertainties, differ from the predictions of the standard solar model by 2 and 3 , respectively.

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