Analysis Of Solar Neutrino Data Research Articles

Solar neutrino measurements using the full data period of Super-Kamiokande-IV

An analysis of solar neutrino data from the fourth phase of Super-Kamiokande (SK-IV) from October 2008 to May 2018 is performed and the results are presented. The observation time of the dataset of SK-IV corresponds to 2970 days and the total live time for all four phases is 5805 days. For more precise solar neutrino measurements, several improvements are applied in this analysis: lowering the data acquisition threshold in May 2015, further reduction of the spallation background using neutron clustering events, precise energy reconstruction considering the time variation of the PMT gain. The observed number of solar neutrino events in 3.49–19.49 MeV electron kinetic energy region during SK-IV is 65,443−388+390(stat.)±925(syst.) events. Corresponding B8 solar neutrino flux is (2.314±0.014(stat.)±0.040(syst.))×106 cm−2 s−1, assuming a pure electron-neutrino flavor component without neutrino oscillations. The flux combined with all SK phases up to SK-IV is (2.336±0.011(stat.)±0.043(syst.))×106 cm−2 s−1. Based on the neutrino oscillation analysis from all solar experiments, including the SK 5805 days dataset, the best-fit neutrino oscillation parameters are sin2θ12,solar=0.306±0.013 and Δm21,solar2=(6.10−0.81+0.95)×10−5 eV2, with a deviation of about 1.5σ from the Δm212 parameter obtained by KamLAND. The best-fit neutrino oscillation parameters obtained from all solar experiments and KamLAND are sin2θ12,global=0.307±0.012 and Δm21,global2=(7.50−0.18+0.19)×10−5 eV2. Published by the American Physical Society 2024

Observation of CNO cycle solar neutrinos in Borexino

The Borexino detector, located at the Laboratori Nazionali del Gran Sasso in Italy, is a radiopure 280 ton liquid scintillator detector with a primary goal to measure low-energy solar neutrinos created in the core of the Sun. These neutrinos are a consequence of nuclear fusion reactions in the solar core where Hydrogen is burned into Helium and provide a direct probe of the energy production processes, namely the proton-proton (pp) chain and the Carbon-Nitrogen-Oxygen (CNO) cycle. The fusion of Hydrogen in the case of the CNO cycle, which is expected to contribute in the order of less than 1% to the total solar energy, is catalyzed by Carbon, Nitrogen, and Oxygen directly depending on the abundances of these elements in the solar core. The measurement of CNO neutrinos is challenging due to the high spectral correlation with the decay electrons of the background isotope 210Bi and the pep solar neutrino signal. The experimental achievement of thermal stabilization of the Borexino detector after mid 2016, has opened the possibility to develop a method to constrain the 210Bi rate through its decay daughter and α emitter 210Po which can be identified in Borexino with an efficiency close to 100 percent on an event-by-event basis. Moreover, the flux of pep neutrinos can be constrained precisely through a global analysis of solar neutrino data which is independent of the dataset used for the CNO analysis. This conference contribution is dedicated to the first experimental evidence of neutrinos produced in the CNO fusion cycle in the Sun which is at the same time the dominant energy production mechanism in heavier stars compared to the Sun.

The luminosity constraint in the era of precision solar physics

The luminosity constraint is a very precise relationship linking the power released by the Sun as photons and the solar neutrino fluxes. Such a relation, which is a direct consequence of the physical processes controlling the production and the transport of energy in the solar interior, is of great importance for the studies of solar neutrinos and has a special role for the search of neutrinos from the CNO cycle, whose first detection with a 5σ significance has been recently announced by the Borexino collaboration. Here we revise the luminosity constraint, discussing and validating its underlying hypotheses, in the light of latest solar neutrino and luminosity measurements. We generalize the current formulation of the luminosity constraint relation so that it can be easily used in future analysis of solar neutrino data, and we provide a specific application showing the link between CNO and pp neutrino fluxes.

Detecting CNO solar neutrinos in next-generation xenon dark matter experiments

We study the prospects for measuring the low-energy components of the solar neutrino flux in future direct dark matter detection experiments. We show that for a depletion of $^{136}$Xe by a factor of 100 relative to its natural abundance, and an extension to electron recoil energies of $\sim$ MeV, future xenon experiments with exposure $\sim 200$ ton-yr can detect the CNO component of the solar neutrino flux at $\sim 3 \sigma$ significance. A CNO detection will provide important insight into metallicity of the solar interior. Precise measurement of low-energy solar neutrinos, including as $pp$, $^7$Be, and $pep$ components, will further improve constraints on the "neutrino luminosity" of the Sun, thereby providing constraints on alternative sources of energy production. We find that a measurement of $L_{\nu}/L_{\odot}$ of order one percent is possible with the above exposure, improving on current bounds from a global analysis of solar neutrino data by a factor of about seven.

Analysis of Solar Neutrino Data from Super-Kamiokande I and II

We are going back to the roots of the original solar neutrino problem: the analysis of data from solar neutrino experiments. The application of standard deviation analysis (SDA) and diffusion entropy analysis (DEA) to the Super-Kamiokande I and II data reveals that they represent a non-Gaussian signal. The Hurst exponent is different from the scaling exponent of the probability density function, and both the Hurst exponent and scaling exponent of the probability density function of the Super-Kamiokande data deviate considerably from the value of 0.5, which indicates that the statistics of the underlying phenomenon is anomalous. To develop a road to the possible interpretation of this finding, we utilize Mathai’s pathway model and consider fractional reaction and fractional diffusion as possible explanations of the non-Gaussian content of the Super-Kamiokande data.

Upper Bound on θ13 from Combined Analysis of Solar Neutrino Data Together with Reactor Data

A joint analysis of solar neutrino data together with the new KamLAND data is presented with different confidence intervals and sin 2 (2θ 13 ) values. It is investigated how the allowed regions are effected in those cases. Limits on sin 2 (2θ 13 ) value are found at different confidence level intervals: sin 2 (2θ 13 ) < 0.19, 0.23 at % 90 CL and % 95 CL respectively.

Combined analysis of all three phases of solar neutrino data from the Sudbury Neutrino Observatory

We report results from a combined analysis of solar neutrino data from all phases of the Sudbury Neutrino Observatory. By exploiting particle identification information obtained from the proportional counters installed during the third phase, this analysis improved background rejection in that phase of the experiment. The combined analysis resulted in a total flux of active neutrino flavors from 8B decays in the Sun of (5.25 \pm 0.16(stat.)+0.11-0.13(syst.))\times10^6 cm^{-2}s^{-1}. A two-flavor neutrino oscillation analysis yielded \Deltam^2_{21} = (5.6^{+1.9}_{-1.4})\times10^{-5} eV^2 and tan^2{\theta}_{12}= 0.427^{+0.033}_{-0.029}. A three-flavor neutrino oscillation analysis combining this result with results of all other solar neutrino experiments and the KamLAND experiment yielded \Deltam^2_{21} = (7.41^{+0.21}_{-0.19})\times10^{-5} eV^2, tan^2{\theta}_{12} = 0.446^{+0.030}_{-0.029}, and sin^2{\theta}_{13} = (2.5^{+1.8}_{-1.5})\times10^{-2}. This implied an upper bound of sin^2{\theta}_{13} < 0.053 at the 95% confidence level (C.L.).

Spectral content of 22Na/44Ti decay data: implications for a solar influence

We report a reanalysis of data on the measured decay rate ratio $^{22}$Na/$^{44}$Ti which were originally published by Norman et al., and interpreted as supporting the conventional hypothesis that nuclear decay rates are constant and not affected by outside influences. We find upon a more detailed analysis of both the amplitude and the phase of the Norman data that they actually favor the presence of an annual variation in $^{22}$Na/$^{44}$Ti, albeit weakly. Moreover, this conclusion holds for a broad range of parameters describing the amplitude and phase of an annual sinusoidal variation in these data. The results from this and related analyses underscore the growing importance of phase considerations in understanding the possible influence of the Sun on nuclear decays. Our conclusions with respect to the phase of the Norman data are consistent with independent analyses of solar neutrino data obtained at Super-Kamiokande-I and the Sudbury Neutrino Observatory (SNO).

Final results from SNO

We report results from a combined analysis of solar neutrino data from all phases of the Sudbury Neutrino Observatory. By exploiting particle identification information obtained from the proportional counters installed during the third phase, this analysis improved background rejection in that phase of the experiment. The combined analysis resulted in a total flux of active neutrino flavors from 8B decays in the Sun of (5.25 ± 0.16(stat.)+0.11−0.13(syst.)) × 106cm−2s−1. A three-flavor neutrino oscillation analysis combining this result with results of all other solar neutrino experiments and the KamLAND experiment yielded Δm221 = (7.4l+0.21−0.19) × l0−5eV2, tan2 θ12 = 0.446+0.030−0.029, and sin2 θ13 = (2.5+1.8−1.5) × 10−2. This implied an upper bound of sin2 θ13 < 0.053 at the 95% confidence level (C.L.).

How does the RSFP scenario effect the Solar neutrino data

A joint analysis of solar neutrino data together with the latest KamLAND data is presented in the RSFP framework using the Wood-Saxon Shape of the Magnetic Field. It is investigatedthat how the latest KamLAND data eects the allowed regions at different muB values. A limiton muB value is found at the different condence level intervals. It is shown that the RSFP scenerio does not have a crucial role on the solar neutrino data.

A BAYESIAN ASSESSMENT OF P-VALUES FOR SIGNIFICANCE ESTIMATION OF POWER SPECTRA AND AN ALTERNATIVE PROCEDURE, WITH APPLICATION TO SOLAR NEUTRINO DATA

The usual procedure for estimating the significance of a peak in a power spectrum is to calculate the probability of obtaining that value or a larger value by chance (known as the p-value), on the assumption that the time series contains only noise - typically that the measurements are derived from random samplings of a Gaussian distribution. We really need to know the probability that the time series is - or is not - compatible with the null hypothesis that the measurements are derived from noise. This probability can be calculated by Bayesian analysis, but this requires one to specify and evaluate a second hypothesis, that the time series does contain a contribution other than noise. We approach the problem of identifying this function in two ways. We first propose three simple conditions that it seems reasonable to impose on this function, and show that these conditions may be satisfied by a simple function with one free parameter. We then define two different ways of combining information derived from two independent power estimates. We find that this consistency condition may be satisfied, to good approximation, by a special case of the previously proposed likelihood function. We find that the resulting significance estimates are considerably more conservative than those usually associated with the p-values. As two examples, we apply the new procedure to two recent analyses of solar neutrino data: (a) power spectrum analysis of Super-Kamiokande data, and (b) the combined analysis of radiochemical neutrino data and irradiance data.

Combined Analysis of Solar Neutrino Data within The RSFP Framework Together with New KamLAND Data

A combined analysis of solar neutrino data together with the new KamLAND data is presented in the RSFP framework. It is investigated how the allowed regions are effected from the new KamLAND data at different \mu B values. Limits on \mu B value is found at the different confidence level intervals.

Global analysis of solar neutrinos (assumed to be Majorana particles) together with the new KamLAND data in the RSFP framework

Assuming neutrinos are Majorana particles having non-zero transition magnetic moments, a global analysis of solar neutrino data, together with the new KamLAND data, is presented in the resonant spin flavour precession (RSFP) framework. We used Wood–Saxon and Gaussian shaped magnetic field profiles throughout the entire Sun. For each magnetic field profile, allowed regions from solar data combined with the new KamLAND data are examined at 95% confidence level (CL). We show that all allowed regions are in the large mixing angle (LMA) region and remain the same as the μB value is increased for both magnetic field profiles, contrary to the Dirac case studied in our previous work. The electron antineutrino flux from the Sun is calculated, and via the results obtained several limits are set for μB.

Enhanced solar antineutrino flux in random magnetic fields

We discuss the impact of the recent KamLAND constraint on the solar anti-neutrino flux on the analysis of solar neutrino data in the presence of Majorana neutrino transition magnetic moments and solar magnetic fields. We consider different stationary solar magnetic field models, both regular and random, highlighting the strong enhancement in the anti-neutrino production rates that characterize turbulent solar magnetic field models. Moreover, we show that for such magnetic fields inside the Sun, one can constrain the intrinsic neutrino magnetic moment down to the level of mu_nu lessthan few times 10^-12 x mu_B irrespective of details of the underlying turbulence model. This limit is more stringent than all current experimental sensitivities, and similar to the most stringent bounds obtained from stellar cooling. We also comment on the robustness of this limit and show that at most it might be weakened by one order of magnitude, under very unlikely circumstances.

Implications of the first neutral current data from SNO for solar neutrino oscillation

We perform model independent and model dependent analyses of solar neutrino data including the neutral current event rate from SNO. The inclusion of the first SNO NC data in the model independent analysis determines the allowed ranges of 8B flux normalisation and the ν e survival probability more precisely than what was possible from the SK and SNO CC combination. We perform global ν e –ν active oscillation analyses of solar neutrino data using the NC rate instead of the SSM prediction for the 8B flux, in view of the large uncertainty in the latter. The LMA gives the best solution, while the LOW solution is allowed only at the 3σ level.

Model independent information on solar neutrino oscillations

We present the results of a Bayesian analysis of solar neutrino data in terms of nu_e->nu_{mu,tau} oscillations, independent from the Standard Solar Model predictions for the solar neutrino fluxes. We show that such a model independent analysis allows to constraint the values of the neutrino mixing parameters in limited regions around the usual SMA, LMA, LOW and VO regions. Furthermore, there is a strong indication in favor of large neutrino mixing and large values of Delta m^2 (LMA region). We calculate also the allowed ranges of the neutrino fluxes and we show that they are in good agreement with the Standard Solar Model prediction. In particular, the ratio of the 8B flux with its Standard Solar Model prediction is constrained in the interval [0.45,1.42] with 99.73% probability. Finally, we show that the hypothesis of no neutrino oscillations is strongly disfavored in a model independent way with respect to the hypothesis of neutrino oscillations.

The luminosity constraint on solar neutrino fluxes

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.

Bayesian view of solar neutrino oscillations

We present the results of a Bayesian analysis of solar neutrino data in terms of nu_e->nu_{mu,tau} and nu_e->nu_s oscillations, where nu_s is a sterile neutrino. We perform a Rates Analysis of the rates of solar neutrino experiments, including the first SNO CC result, and spectral data of the CHOOZ experiment, and a Global Analysis that takes into account also the Super-Kamiokande day and night electron energy spectra. We show that the Bayesian analysis does not suffer any problem from the inclusion of the numerous bins of the CHOOZ and Super-Kamiokande energy spectra and allows to reach the same conclusions on the favored type of neutrino transitions and on the determination of the most favored values of the oscillation parameters in both the Rates and Global Analysis. Our Bayesian analysis shows that nu_e->nu_s transitions are strongly disfavored with respect to nu_e->nu_{mu,tau} transitions. In the case of nu_e->nu_{mu,tau} oscillations, the LMA region is favored by the data (86% probability), the LOW region has some small chance (13% probability), the VO region is almost excluded (1% probability) and the SMA region is practically excluded (0.01% probability). We calculate also the marginal posterior probability distributions for tan^2 theta and Delta m^2 and we show that the data imply large mixing almost with certainty and large values of Delta m^2 are favored. We present also the results of a standard least-squares analysis and we show that the standard goodness of fit test is not able to rejects pure nu_e->nu_s transitions. The likelihood ratio test allows to reject pure nu_e->nu_s transitions in favor of nu_e->nu_{mu,tau} transitions only in the Global Analysis.

Global oscillation analysis of solar neutrino data with helioseismically constrained fluxes

A seismic model for the Sun calculated using the accurate helioseismic data predicts a lower ${}^{8}\mathrm{B}$ neutrino flux as compared to the standard solar model (SSM). However, there persists a discrepancy between the predicted and measured neutrino fluxes and it seems necessary to invoke neutrino oscillations to explain the measurements. In this work, we have performed a global, unified oscillation analysis of the latest solar neutrino data (including the results of SNO charged current rate) using the seismic model fluxes as theoretical predictions. We determine the best-fit values of the neutrino oscillation parameters and the ${\ensuremath{\chi}}_{\mathrm{min}}^{2}$ for both ${\ensuremath{\nu}}_{e}\ensuremath{-}{\ensuremath{\nu}}_{\mathrm{active}}$ and ${\ensuremath{\nu}}_{e}\ensuremath{-}{\ensuremath{\nu}}_{\mathrm{sterile}}$ cases and present the allowed parameter regions in the $\ensuremath{\Delta}{m}^{2}\ensuremath{-}{\mathrm{tan}}^{2}\ensuremath{\theta}$ plane for ${\ensuremath{\nu}}_{e}\ensuremath{-}{\ensuremath{\nu}}_{\mathrm{active}}$ transition. The results are compared with those obtained using the latest SSM by Bahcall and co-workers.

A frequentist analysis of solar neutrino data

We present a Monte Carlo analysis of solar neutrino data in terms of neutrino oscillations in the framework of frequentist statistics. We show that the goodness of fit and the confidence level of the allowed regions in the space of the neutrino oscillation parameters are significantly overestimated in the standard method. We also present a calculation of exact allowed regions with correct frequentist coverage. We show that the exact VO, LMA and LOW regions are much larger than the standard ones and merge together giving an allowed band at large mixing angle for all Δ m 2 ≳ 10 −10 eV 2.