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Register a new userMeasurements of the atmospheric neutrino flux by Super-Kamiokande: energy spectra, geomagnetic effects, and solar modulation
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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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While neutrino physics enters precision era, several important unknowns remain. Atmospheric neutrinos allow to simultaneously test key oscillation parameters, with Super-Kamiokande experiment playing a central role. We discuss results from atmospheric neutrino oscillation analysis of the full dataset from Super-Kamiokande I-IV phases. Further, we discuss tests of non-standard neutrino interactions with atmospheric neutrinos in Super-Kamiokande.
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.
GUT monopoles captured by the Suns gravitation are expected to catalyze proton decays via the Callan-Rubakov process. In this scenario, protons, which initially decay into pions, will ultimately produce u_{e}, u_{mu} and bar{ u}_{mu}. After undergoing neutrino oscillation, all neutrino species appear when they arrive at the Earth, and can be detected by a 50,000 metric ton water Cherenkov detector, Super-Kamiokande (SK). A search for low energy neutrinos in the electron total energy range from 19 to 55 MeV was carried out with SK and gives a monopole flux limit of F_M(sigma_0/1 mb) < 6.3 times 10^{-24} (beta_M/10^{-3})^2 cm^{-2} s^{-1} sr^{-1} at 90% C.L., where beta_M is the monopole velocity in units of the speed of light and sigma_0 is the catalysis cross section at beta_M=1. The obtained limit is more than eight orders of magnitude more stringent than the current best cosmic-ray supermassive monopole flux limit, F_M < 1 times 10^{-15} cm^{-2} s^{-1} sr^{-1} for beta_M < 10^{-3} and also two orders of magnitude lower than the result of the Kamiokande experiment, which used a similar detection method.
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..
Galactic cosmic-ray (GCR) flux short-term variations ($<$1 month) in the inner heliosphere are mainly associated with the passage of high-speed solar wind streams (HSS) and interplanetary (IP) counterparts of coronal mass ejections (ICMEs). Data gathered with a particle detector flown on board the ESA LISA Pathfinder (LPF) spacecraft, during the declining part of the solar cycle 24 (February 2016 - July 2017) around the Lagrange point L1, have allowed to study the characteristics of recurrent cosmic-ray flux modulations above 70 MeV n$^{-1}$. %These modulations are observed when the solar wind speed is $>$ 400 km s$^{-1}$ and/or the IP magnetic field intensity $>$ 10 nT. It is shown that the amplitude and evolution of individual modulations depend in a unique way on both IP plasma parameters and particle flux intensity before HSS and ICMEs transit. By comparing the LPF data with those gathered contemporaneously with the magnetic spectrometer experiment AMS-02 on board the International Space Station and with those of Earth polar neutron monitors, the GCR flux modulation was studied at different energies during recurrent short-term variations. It is also aimed to set the near real-time particle observation requirements to disentangle the role of long and short-term variations of the GCR flux to evaluate the performance of high-sensitivity instruments in space such as the future interferometers for gravitational wave detection. Finally, the association between recurrent GCR flux variation observations in L1 and weak to moderate geomagnetic activity in 2016-2017 is discussed. Short-term recurrent GCR flux variations are good proxies of recurrent geomagnetic activity when the B$_z$ component of the IP magnetic field is directed northern.
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