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Register a new userSolar Neutrino Measurements in Super-Kamiokande-IV
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Upgraded electronics, improved water system dynamics, better calibration and analysis techniques allowed Super-Kamiokande-IV to clearly observe very low-energy 8B solar neutrino interactions, with recoil electron kinetic energies as low as 3.49 MeV. Super-Kamiokande-IV data-taking began in September of 2008; this paper includes data until February 2014, a total livetime of 1664 days. The measured solar neutrino flux is (2.308+-0.020(stat.) + 0.039-0.040(syst.)) x 106/(cm2sec) assuming no oscillations. The observed recoil electron energy spectrum is consistent with no distortions due to neutrino oscillations. An extended maximum likelihood fit to the amplitude of the expected solar zenith angle variation of the neutrino-electron elastic scattering rate in SK-IV results in a day/night asymmetry of (-3.6+-1.6(stat.)+-0.6(syst.))%. The SK-IV solar neutrino data determine the solar mixing angle as sin2 theta_12 = 0.327+0.026-0.031, all SK solar data (SK-I, SK-II, SK III and SKIV) measures this angle to be sin2 theta_12 = 0.334+0.027-0.023, the determined mass-squared splitting is Delta m2_21 = 4.8+1.5-0.8 x10-5 eV2.
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Due to a very low production rate of electron anti-neutrinos ($bar{ u}_e$) via nuclear fusion in the Sun, we expect to see $bar{ u}_e$ from other contribution. An appearance of $bar{ u}_e$ in solar neutrino flux opens a new window for the new physics beyond the standard model. In particular, a spin-flavor precession process is expected to convert an electron neutrino into an electron anti-neutrino (${ u_etobar{ u}_e}$) if neutrino has a finite magnetic moment. In this work, we have searched for solar $bar{ u}_e$ in the Super-Kamiokande experiment, using neutron tagging to identify their inverse beta decay signature. We identified 78 $bar{ u}_e$ candidates for neutrino energies of 9.3 to 17.3 MeV in 2970.1 live days with a fiducial volume of 22.5 kiloton water (183.0 kton$cdot$year exposure). The energy spectrum has been consistent with background predictions and we thus derived a 90% confidence level upper limit of ${3.6times10^{-4}}$ on the $ u_etobar{ u}_e$ conversion probability in the Sun. We used this result to evaluate the sensitivity of future experiments, notably the Super-Kamiokande Gadolinium (SK-Gd) upgrade.
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 8B solar flux in the 5.0 to 20 MeV total electron energy region is 2.32+/-0.04 (stat.)+/-0.05 (sys.) *10^6 cm^-2sec^-1, 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 sin^2 {theta}12 = 0.30+0.02-0.01(tan^2 {theta}12 = 0.42+0.04 -0.02) and {Delta}m2_21 = 6.2+1.1-1.9 *10^-5eV^2. Combined with KamLAND results, the best-fit oscillation parameters are found to be sin^2 {theta}12 = 0.31+/-0.01(tan^2 {theta}12 = 0.44+/-0.03) and {Delta}m2_21 = 7.6?0.2*10^-5eV^2 . The 8B neutrino flux obtained from global solar neutrino experiments is 5.3+/-0.2(stat.+sys.)*10^6cm^-2s^-1, while the 8B flux becomes 5.1+/-0.1(stat.+sys.)*10^6cm^-2s^-1 by adding KamLAND result. In a three-flavor analysis combining all solar neutrino experiments, the upper limit of sin^2 {theta}13 is 0.060 at 95% C.L.. After combination with KamLAND results, the upper limit of sin^2 {theta}13 is found to be 0.059 at 95% C.L..
A new event reconstruction algorithm based on a maximum likelihood method has been developed for Super-Kamiokande. Its improved kinematic and particle identification capabilities enable the analysis of atmospheric neutrino data in a detector volume 32% larger than previous analyses and increases sensitivity to the neutrino mass hierarchy. Analysis of a 253.9 kton-year exposure of the Super-Kamiokande IV atmospheric neutrino data has yielded a weak preference for the normal hierarchy, disfavoring the inverted hierarchy at 74% assuming oscillations at the best fit of the analysis.
An analysis of atmospheric neutrino data from all four run periods of superk optimized for sensitivity to the neutrino mass hierarchy is presented. Confidence intervals for $Delta m^2_{32}$, $sin^2 theta_{23}$, $sin^2 theta_{13}$ and $delta_{CP}$ are presented for normal neutrino mass hierarchy and inverted neutrino mass hierarchy hypotheses based on atmospheric neutrino data alone. Additional constraints from reactor data on $theta_{13}$ and from published binned T2K data on muon neutrino disappearance and electron neutrino appearance are added to the atmospheric neutrino fit to give enhanced constraints on the above parameters. Over the range of parameters allowed at 90% confidence level, the normal mass hierarchy is favored by between 91.5% and 94.5% based on the combined result.
A comprehensive study on the atmospheric neutrino flux in the energy region from sub-GeV up to several TeV using the Super-Kamiokande water Cherenkov detector is presented in this paper. The energy and azimuthal spectra of the atmospheric ${ u}_e+{bar{ u}}_e$ and ${ u}_{mu}+{bar{ u}}_{mu}$ fluxes are measured. The energy spectra are obtained using an iterative unfolding method by combining various event topologies with differing energy responses. The azimuthal spectra depending on energy and zenith angle, and their modulation by geomagnetic effects, are also studied. A predicted east-west asymmetry is observed in both the ${ u}_e$ and ${ u}_{mu}$ samples at 8.0 {sigma} and 6.0 {sigma} significance, respectively, and an indication that the asymmetry dipole angle changes depending on the zenith angle was seen at the 2.2 {sigma} level. The measured energy and azimuthal spectra are consistent with the current flux models within the estimated systematic uncertainties. A study of the long-term correlation between the atmospheric neutrino flux and the solar magnetic activity cycle is also performed, and a weak indication of a correlation was seen at the 1.1 {sigma} level, using SK I-IV data spanning a 20 year period. For particularly strong solar activity periods known as Forbush decreases, no theoretical prediction is available, but a deviation below the typical neutrino event rate is seen at the 2.4 {sigma} level.
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