Determination of solar neutrino oscillation parameters using 1496 days of Super-Kamiokande-I data (original) (raw)
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Constraints on Neutrino Oscillations Using 1258 Days of Super-Kamiokande Solar Neutrino Data
Physical Review Letters, 2001
We report the result of a search for neutrino oscillations using precise measurements of the recoil electron energy spectrum and zenith angle variations of the solar neutrino ux from 1258 days of neutrino-electron scattering data in Super-Kamiokande. The absence of signi cant zenith angle variation and spectrum distortion places strong constraints on neutrino mixing and mass di erence in a ux-independent w ay. Using the Super-Kamiokande ux measurement i n addition, two allowed regions at large mixing are found.
Determining the oscillation parameters by solar neutrinos and KamLAND
Physics Letters Section B, 2003
The neutrino oscillation experiment KamLAND has provided us with the first evidence for ν¯e disappearance, coming from nuclear reactors. We have combined their data with all solar neutrino data, assuming two flavor neutrino mixing, and obtained allowed parameter regions which are compatible with the so-called large mixing angle MSW solution to the solar neutrino problem. The allowed regions in the plane of mixing angle and mass squared difference are now split into two islands at 99% C.L. We have speculated how these two islands can be distinguished in the near future. We have shown that a 50% reduction of the error on SNO neutral-current measurement can be important in establishing in each of these islands the true values of these parameters lie. We also have simulated KamLAND positron energy spectrum after 1 year of data taking, assuming the current best fitted values of the oscillation parameters, combined it the with current solar neutrino data and showed how these two split islands can be modified.
Phys Rev D, 2002
What can we learn from solar neutrino observations? Is there any solution to the solar neutrino anomaly which is favored by the present experimental panorama? After SNO results, is it possible to affirm that neutrinos have mass? In order to answer such questions we analyze the current available data from the solar neutrino experiments, including the recent SNO result, in view of many acceptable solutions to the solar neutrino problem based on different conversion mechanisms, for the first time using the same statistical procedure. This allows us to do a direct comparison of the goodness of the fit among different solutions, from which we can discuss and conclude on the current status of each proposed dynamical mechanism. These solutions are based on different assumptions: (a) neutrino mass and mixing, (b) a nonvanishing neutrino magnetic moment, (c) the existence of nonstandard flavor-changing and nonuniversal neutrino interactions, and (d) a tiny violation of the equivalence principle. We investigate the quality of the fit provided by each one of these solutions not only to the total rate measured by all the solar neutrino experiments but also to the recoil electron energy spectrum measured at different zenith angles by the Super-Kamiokande Collaboration. We conclude that several nonstandard neutrino flavor conversion mechanisms provide a very good fit to the experimental data which is comparable with (or even slightly better than) the most famous solution to the solar neutrino anomaly based on the neutrino oscillation induced by mass.
Constraining neutrino oscillation parameters with current solar and atmospheric data
Physical Review D, 2003
We analyze the impact of recent solar and atmospheric data in the determination of the neutrino oscillation parameters, taking into account that both the solar ν e and the atmospheric ν µ may convert to a mixture of active and sterile neutrinos. We use the most recent global solar neutrino data, including the 1496-day Super-K neutrino data sample, and we investigate in detail the impact of the recent SNO neutral current, spectral and day/night data by performing also an analysis using only the charged current rate from SNO. We confirm the clear preference of the pure active LMA solution of the solar neutrino problem and obtain that the LOW, VAC, SMA and Just-So 2 solutions are disfavored with a ∆χ 2 = 9, 9, 23, 31, respectively. Furthermore, we find that the global solar data constrains the admixture of a sterile neutrino to be less than 44% at 99% C.L..
Analysis of Super‐Kamiokande 5 Day Measurements of the Solar Neutrino Flux
The Astrophysical Journal, 2004
Data in 5-day bins, recently released by the Super-Kamiodande Consortium, has been analyzed by a likelihood procedure that has certain advantages over the Lomb-Scargle procedure used by the consortium. The two most prominent peaks in the power spectrum of the 10-day data were at 9.42 y-1 and 26.57 y-1 , and it was clear that one was an alias of the other caused by the regularity of the binning. There were reasons to believe that the 9.42 y-1 peak was an alias of the 26.57 y-1 peak, but analysis of the 5-day data makes it clear that the reverse is the case. In addition to a strong peak near 9.42 y-1 , we find peaks at 43.72 y-1 and at 39.28 y-1. After comparing this analysis with a power-spectrum analysis of magnetic-field data, we suggest that these three peaks may be attributed to a harmonic of the solar rotation rate and to an r-mode oscillation with spherical harmonic indices l = 2, m = 2.
Evidence for solar neutrino flux variability and its implications
Astroparticle Physics, 2005
Although KamLAND apparently rules out Resonant-Spin-Flavor-Precession (RSFP) as an explanation of the solar neutrino deficit, the solar neutrino fluxes in the Cl and Ga experiments appear to vary with solar rotation. Added to this evidence, summarized here, a power spectrum analysis of the Super-Kamiokande data reveals significant variation in the flux matching a dominant rotation rate observed in the solar magnetic field in the same time period. Three frequency peaks, all related to this rotation rate, can be explained quantitatively. A Super-Kamiokande paper reported no time variation of the flux, but showed the same peaks, there interpreted as statistically insignificant, due to an inappropriate analysis. This modulation is small (7%) in the Super-Kamiokande energy region (and below the sensitivity of the Super-Kamiokande analysis) and is consistent with RSFP as a subdominant neutrino process in the convection zone. The data display effects that correspond to solar-cycle changes in the magnetic field, typical of the convection zone. This subdominant process requires new physics: a large neutrino transition magnetic moment and a light sterile neutrino, since an effect of this amplitude occurring in the convection zone cannot be achieved with the three known neutrinos. It does, however, resolve current problems in providing fits to all experimental estimates of the mean neutrino flux, and is compatible with the extensive evidence for solar neutrino flux variability.
Physical Review D, 2005
Since rotational or similar modulation of the solar neutrino flux would seem to be incompatible with the currently accepted theoretical interpretation of the solar neutrino deficit, it is important to determine whether or not such modulation occurs. There have been conflicting claims as to whether or not power-spectrum analysis of the Super-Kamiokande solar neutrino data yields evidence of variability. Comparison of these claims is complicated by the fact that the relevant articles may use different datasets, different methods of analysis, and different procedures for significance estimation. The purpose of this article is to clarify the role of power spectrum analysis. To this end, we analyze primarily the Super-Kamiokande 5-day dataset, and we use a standard procedure for significance estimation as used by the Super-Kamiokande collaboration. We then analyze this dataset, with this method of significance estimation, using six methods of power spectrum analysis. Five of these have been used in published articles, and the other is a method that might have been used. We find that, with one exception, the results of these calculations are consistent with those of previously published analyses. We find that the power of the principal modulation (that at 9.43 yr-1) is greater in analyses that take account of error estimates than in the basic Lomb-Scargle analysis that does not take account of error estimates. The corresponding significance level reaches 99.3% for one method of analysis. However, we find a problem with the recent article by Koshio: we can reproduce the results of his power-spectrum analysis, but not the 2 results of his Monte-Carlo simulations. We have a suggestion that may account for the difference. We also comment on a recent article by Yoo et al. We discuss, in terms of subdominant processes, possible neutrino-physics interpretations of the apparent variability of the Super-Kamiokande measurements, and we suggest steps that could be taken to resolve the question of variability of the solar neutrino flux.
Solar neutrino results in Super-Kamiokande-III
Physical Review D, 2011
The results of the third phase of the Super-Kamiokande solar neutrino measurement are presented and compared to the first and second phase results. With improved detector calibrations, a full detector simulation, and improved analysis methods, the systematic uncertainty on the total neutrino flux is estimated to be ±2.1%, which is about two thirds of the systematic uncertainty for the first phase of Super-Kamiokande. The observed B8 solar flux in the 5.0 to 20 MeV total electron energy region is 2.32±0.04(stat)±0.05(sys)×106cm-2sec-1 under the assumption of pure electron-flavor content, in agreement with previous measurements. A combined oscillation analysis is carried out using SK-I, II, and III data, and the results are also combined with the results of other solar neutrino experiments. The best-fit oscillation parameters are obtained to be sin2θ12=0.30-0.01+0.02(tan2θ12=0.42-0.02+0.04) and Δm212=6.2-1.9+1.1×10-5eV2. Combined with KamLAND results, the best-fit oscillation parameters are found to be sin2θ12=0.31±0.01(tan2θ12=0.44±0.03) and Δm212=7.6±0.2×10-5eV2. The B8 neutrino flux obtained from global solar neutrino experiments is 5.3±0.2(stat+sys)×106cm-2s-1, while the B8 flux becomes 5.1±0.1(stat+sys)×106cm-2s-1 by adding KamLAND results. In a three-flavor analysis combining all solar neutrino experiments, the upper limit of sin2θ13 is 0.060 at 95% C.L.. After combination with KamLAND results, the upper limit of sin2θ13 is found to be 0.059 at 95% C.L.
ON RECONCILING ATMOSPHERIC, LSND, AND SOLAR NEUTRINO-OSCILLATION DATA
Modern Physics Letters A, 1998
The L/E-flatness of the e-like events observed in the recent atmospheric-neutrino data from Super-Kamiokande (SuperK) is interpreted to reflect a new symmetry of the neutrino-oscillation mixing matrix. From that we obtain an analytical set of constraints yielding a class of mixing matrices of the property to simultaneously fit both the Su-perK and the LSND data. The resulting mass squared difference relevant for the LSND experiment is found as 0.3 eV 2 . The discussed symmetry, e.g., carries the nature that expectation values of masses for νµ and ντ are identical. These considerations are purely data dictated. A different framework is then applied to the solar neutrino problem. It is argued that a single sterile neutrino is an unlikely candidate to accommodate the data from the four solar neutrino experiments. A scenario is discussed which violates CPT symmetry, and favors the νe-νe system to belong to the 'self'-'anti-self' charge conjugate construct in the (1/2, 0) ⊕ (0, 1/2) representation space, where the needed helicity flipping amplitudes are preferred, rather than the usual Dirac, or Majorana, constructs. In the presented framework the emerging SuperK data on solar neutrino flux is reconciled with the Homestake, GALLEX, and SAGE experiments. This happens because the former detects not only the solar νe but also, at a lower cross section, the oscillated solar νe; while the latter are sensitive only to the oscillation-diminished solar νe flux. A direct observation of solar νe by SNO will confirm our scenario. Finally, we consider the possibility for flavor-dependent gravitational couplings of neutrinos as emerging out of the noncommutativity of the quantum operators associated with the measurements of energy and flavor.