Determining the oscillation parameters by solar neutrinos and KamLAND (original) (raw)
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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..
Determination of solar neutrino oscillation parameters using 1496 days of Super-Kamiokande-I data
Physics Letters B, 2002
A number of different fits to solar neutrino mixing and mass square difference were performed using 1496 days of Super-Kamiokande-I's solar neutrino data. These data select two allowed areas at large neutrino mixing when combined with either the solar 8 B flux prediction of the standard solar model or the SNO interaction rate measurements. A global fit combining SK data with the solar neutrino interaction rates measured by Homestake, SNO, Gallex/GNO and SAGE prefers a single allowed area, the Large Mixing Angle solution, at the 98.9% confidence level. The mass square difference ∆m 2 between the two mass eigenstates ranges from about 3 to 19 × 10 −5 eV 2 , while the mixing angle θ is in the range of tan 2 θ ≈0.25-0.65.
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.
Global Analysis of Solar Neutrino and KamLAND Data
Journal of Physics G-nuclear and Particle Physics, 2003
A global analysis of the data from all the solar neutrino experiments combined with the recent KamLAND data is presented. A formula frequently used in the literature gives survival probability for three active solar neutrino flavors in terms of a suitably-modified two-flavor survival probability. Corrections to this formula, which depend on theta13\theta_{13}theta13 and deltam312\delta m_{31}^2deltam312, are calculated. For the mass scale suggested by the atmospheric neutrino experiments the contributions of deltam312\delta m_{31}^2deltam312 to these corrections is found to be negligible. The role of theta13\theta_{13}theta13 in solar neutrino physics is elaborated. For electron neutrino oscillations into another active flavor, we find best fit values of tan2theta12sim0.46\tan^2 \theta_{12} \sim 0.46tan2theta12sim0.46, tan2theta13sim0\tan^2 \theta_{13} \sim 0tan2theta13sim0, and deltam212sim7.1times10−5\delta m_{21}^2 \sim 7.1 \times 10^{-5}deltam212sim7.1times10−5 eV$^2$. It is found that the combined solar neutrino and KamLAND date provide the limit cos4theta13<0.8\cos^4 \theta_{13} < 0.8cos4theta13<0.8 at the 90 % confidence level.
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.
Measurement of Neutrino Oscillation with KamLAND: Evidence of Spectral Distortion
J. Learned, A. Young, C. Lane, Z. Djurcic, Bruce Berger, Y. Kamyshkov, 康宏 岸本, Jason Detwiler, Y. Efremenko, Sanshiro Enomoto, Brian K Fujikawa, A. Piepke, K. Heeger
Physical Review Letters, 2005
We present results of a study of neutrino oscillation based on a 766 ton-year exposure of KamLAND to reactor anti-neutrinos. We observe 258 νe candidate events with energies above 3.4 MeV compared to 365.2 events expected in the absence of neutrino oscillation. Accounting for 17.8 expected background events, the statistical significance for reactor νe disappearance is 99.998%. The observed energy spectrum disagrees with the expected spectral shape in the absence of neutrino oscillation at 99.6% significance and prefers the distortion expected from νe oscillation effects. A two-neutrino oscillation analysis of the KamLAND data gives ∆m 2 = 7.9 +0.6 −0.5 ×10 −5 eV 2 . A global analysis of data from KamLAND and solar neutrino experiments yields ∆m 2 = 7.9 +0.6 −0.5 ×10 −5 eV 2 and tan 2 θ = 0.40 +0.10 −0.07 , the most precise determination to date. PACS numbers: 14.60.Pq, 26.65.+t, 28.50.Hw
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.
Neutrino physics from new SNO and KamLAND data and future prospects
Physics Letters B, 2005
We analyze the cumulative data from the latest SNO, KamLAND and other solar neutrino experiments in the standard scenario of three oscillating active neutrinos. We determine the solar neutrino oscillation parameters and obtain new bounds on θx. We also place constraints on the fraction of oscillating solar neutrinos that transform to sterile neutrinos with the 8 B flux normalization left free. Concomitantly, we assess the sensitivity of future data from the SNO and KamLAND experiments to θx and to the sterile neutrino content of the solar flux.
Combining the first KamLAND results with solar neutrino data
Physical Review D, 2003
We consider the impact of the recent KamLAND data on neutrino oscillations, the first terrestrial neutrino experiment that can probe the solar neutrino anomaly. By combining the first 145.1 days of KamLAND data with the full sample of latest solar neutrino data we find an enhanced rejection against non-LMA oscillations, allowed only at more than 4σ with respect to LMA. Furthermore, the new data have a strong impact in narrowing down the allowed range of ∆m 2 inside the LMA region. In contrast, our global analysis indicates that the new data have little impact on the location of the best fit point. In particular the solar neutrino mixing remains significantly non-maximal (3σ).
Solar neutrino oscillation diagnostics at SuperKamiokande and Sudbury Neutrino Observatory
Pramana, 1999
Results for solar neutrino detection from the SuperKamiokande collaboration have been presented recently while those from the Sudbury Neutrino Observatory are expected in the near future. These experiments are sensitive to the 8 B neutrinos from the sun, the shape of whose spectrum is well-known but the normalisation is less certain. We propose several variables, insensitive to the absolute flux of the incident beam, which probe the shape of the observed spectrum and can sensitively signal neutrino oscillations. They provide methods to extract the neutrino mixing angle and mass splitting from the data and also to distinguish oscillation to sequential neutrinos from those to a sterile neutrino.