Atmospheric neutrino oscillation analysis with sub-leading effects in Super-Kamiokande I, II, and III
Kamiokande Collaboration, R. Wendell, C. Ishihara, K. Abe, Y. Hayato, T. Iida, M. Ikeda, K. Iyogi, J. Kameda, K. Kobayashi, Y. Koshio, Y. Kozuma, M. Miura, S. M… 展开作者
Kamiokande Collaboration, R. Wendell, C. Ishihara, K. Abe, Y. Hayato, T. Iida, M. Ikeda, K. Iyogi, J. Kameda, K. Kobayashi, Y. Koshio, Y. Kozuma, M. Miura, S. Moriyama, M. Nakahata, S. Nakayama, Y. Obayashi, H. Ogawa, H. Sekiya, M. Shiozawa, Y. Suzuki, A. Takeda, Y. Takenaga, Y. Takeuchi, K. Ueno, K. Ueshima, H. Watanabe, S. Yamada, T. Yokozawa, S. Hazama, H. Kaji, T. Kajita, K. Kaneyuki, T. McLachlan, K. Okumura, Y. Shimizu, N. Tanimoto, M. R. Vagins, F. Dufour, E. Kearns, M. Litos, J. L. Raaf, J. L. Stone, L. R. Sulak, W. Wang, M. Goldhaber, K. Bays, D. Casper, J. P. Cravens, W. R. Kropp, S. Mine, C. Regis, M. B. Smy, H. W. Sobel, K. S. Ganezer, J. Hill, W. E. Keig, J. S. Jang, J. Y. Kim, I. T. Lim, J. Albert, M. Fechner, K. Scholberg, C. W. Walter, S. Tasaka, J. G. Learned, S. Matsuno, Y. Watanabe, T. Hasegawa, T. Ishida, T. Ishii, T. Kobayashi, T. Nakadaira, K. Nakamura, K. Nishikawa, H. Nishino, Y. Oyama, K. Sakashita, T. Sekiguchi, T. Tsukamoto, A. T. Suzuki, A. Minamino, T. Nakaya, Y. Fukuda, Y. Itow, G. Mitsuka, T. Tanaka, C. K. Jung, G. Lopez, C. McGrew, C. Yanagisawa, N. Tamura, H. Ishino, A. Kibayashi, S. Mino, T. Mori, M. Sakuda, H. Toyota, Y. Kuno, M. Yoshida, S. B. Kim, B. S. Yang, T. Ishizuka, H. Okazawa, Y. Choi, K. Nishijima, Y. Yokosawa, M. Koshiba, M. Yokoyama, Y. Totsuka, S. Chen, Y. Heng, Z. Yang, H. Zhang, D. Kielczewska, P. Mijakowski, K. Connolly, M. Dziomba, E. Thrane, R. J. Wilkes
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17 Pages, 14 figures. To be submitted to Phys. Rev. D Minor update to text after referee comments. Figures modified for better grayscale printing.
We present a search for non-zero theta_{13} and deviations of sin^2 theta_{23} from 0.5 in the oscillations of atmospheric neutrino data from Super-Kamiokande -I, -II, and -III. No distortions of the neutrino flux consistent with non-zero theta_{13} are found and both neutrino mass hierarchy hypotheses are in agreement with the data. The data are best fit at Delta m^2 = 2.1 x 10^-3 eV^2, sin^2 theta_{13} = 0.0, and sin^2 theta_{23} =0.5. In the normal (inverted) hierarchy theta_{13} and Delta m^2 are constrained at the one-dimensional 90% C.L. to sin^2 theta_{13} < 0.04 (0.09) and 1.9 (1.7) x 10^-3 < Delta m^2 < 2.6 (2.7) x 10^-3 eV^2. The atmospheric mixing angle is within 0.407 <= sin^2 theta_{23} <= 0.583 at 90% C.L.
New atmospheric neutrino results from Super-Kamiokande are presented. Results from Kamiokande on upward going muons are also presented. All these data, together with the Kamiokande atmospheric neutrino data give evidence for neutrino oscillations. Two flavor nu_mu <-> nu_tau oscillations, with large sin^2(2theta) and Delta-m^2 in the region of 10^-3 to 10^-2, explain all these data.
In 1998, the Super-Kamiokande announced evidence for the observation of neutrino oscillations based on measurements of the atmospheric neutrino flux. This paper presents the updated results for fully and partially-contained events with 736 days of data, as well as upward-going muon results and a global analysis. Preliminary interpretations of the results in terms of various two-flavor oscillation hypotheses are presented.
Atmospheric neutrino and solar neutrino data from the first phase of Super-Kamiokande (SK-I) are presented. The observed data are used to study atmospheric and solar neutrino oscillations. Zenith angle distributions from various atmospheric neutrino data samples are used to estimate the neutrino oscillation parameter region. In addition, a new result of the $L/E$ measurement is presented. A dip in the $L/E$ distribution was observed in the data, as predicted from the sinusoidal flavor transition probability of neutrino oscillation. The energy spectrum and the time variation such as day/night a…
We present a combined analysis of fully-contained, partially-contained and upward-going muon atmospheric neutrino data from a 1489 day exposure of the Super--Kamiokande detector. The data samples span roughly five decades in neutrino energy, from 100 MeV to 10 TeV. A detailed Monte Carlo comparison is described and presented. The data is fit to the Monte Carlo expectation, and is found to be consistent with neutrino oscillations of $ν_μ\leftrightarrow ν_τ$ with $\sin^22θ> 0.92$ and $1.5\times 10^{-3} < Δm^2 < 3.4\times 10^{-3}{\rm eV}^2$ at 90% confidence level.
We present atmospheric neutrino results from a 79 kiloton year (1289 days) exposure of the Super-Kamiokande detector. Our data are well explained by $ν_μ \to ν_τ$ 2-flavor oscillations. We have been attempting to discriminate between the possible oscillating partners of the muon neutrino as being either the tau neutrino or the sterile neutrino. Pure $ν_μ\toν_s$ oscillation is disfavored at 99% C.L.. Moreover, we performed the appearance search for charged current tau neutrino interactions in the upward-going samples. Our data is consistent with $ν_τ$ appearance at roughly the two-sigma level.
We report on the results of a three-flavor oscillation analysis using Super-Kamiokande~I atmospheric neutrino data, with the assumption of one mass scale dominance ($Δm_{12}^2$$=$0). No significant flux change due to matter effect, which occurs when neutrinos propagate inside the Earth for $θ_{13}$$\neq$0, has been seen either in a multi-GeV $ν_e$-rich sample or in a $ν_μ$-rich sample. Both normal and inverted mass hierarchy hypotheses are tested and both are consistent with observation. Using Super-Kamiokande data only, 2-dimensional 90 % confidence allowed regions are obtained: mixing angles…
A strong body of evidence now exists for atmospheric nu_mu disappearance oscillations. Such disappearance could be explained by oscillations to either nu_tau or a ``sterile'' neutrino (nu_s). Super-Kamiokande uses three different methods to distinguish between these two scenarios. First, matter effects would suppress the nu_mu <-> nu_s oscillation amplitude at high energy. Second, oscillation to nu_s would reduce the overall neutral-current neutrino interaction rate. Third, the smoking gun of nu_mu <-> nu_tau oscillations would be the observation of tau appearance resulting from charged-curren…
We consider muon neutrino to tau neutrino oscillations in the context of the Mass Varying Neutrino (MaVaN) model, where the neutrino mass can vary depending on the electron density along the flight path of the neutrino. Our analysis assumes a mechanism with dependence only upon the electron density, hence ordinary matter density, of the medium through which the neutrino travels. Fully-contained, partially-contained and upward-going muon atmospheric neutrino data from the Super--Kamiokande detector, taken from the entire SK--I period of 1489 live days, are compared to MaVaN model predictions. W…
The recent results from Super-Kamiokande (SK) are reported. On atmospheric neutrino analysis, we have performed a full 3-flavor oscillation analysis with SK-I+II+III data. A CPT violation study on atmospheric neutrino is also done with SK-I+II+III data. On solar neutrino analysis, a 3-flavor oscillation analysis with SK-III data is performed.
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.
The Super-Kamiokande experiment has collected more than 11 live-years of atmospheric neutrino data. Atmospheric neutrinos cover a wide phase space in both energy and distance travelled, the parameters relevant for studying neutrino oscillations. We present here recent measurements of the three-flavor neutrino oscillation parameters using this atmospheric neutrino data, as well as new limits on mixing with a fourth sterile neutrino state.
Super-Kamiokande atmospheric neutrino data were fit with an unbinned maximum likelihood method to search for the appearance of tau leptons resulting from the interactions of oscillation-generated tau neutrinos in the detector. Relative to the expectation of unity, the tau normalization is found to be $1.42 \pm 0.35 \ (stat) {\}^{+0.14}_{-0.12}\ (syst) $ excluding the no-tau-appearance hypothesis, for which the normalization would be zero, at the 3.8$σ$ level. We estimate that $180.1 \pm 44.3\ (stat) {\}^{+17.8}_{-15.2}\ (syst)$ tau leptons were produced in the 22.5 kton fiducial volume of the …
The flux of upward through-going muons of minimum (mean) threshold energy > 1.6 (3.0) GeV is measured, based on a total of 372 events observed by the Kamiokande II+III detector during 2456 detector live days. The observed muon flux was (1.94+-0.10(stat.)+0.07-0.06(sys.))*10^-13 /cm^2/s/sr, which is compared to an expected value of (2.46+-0.54(theo.))*10^-13/cm^2/s/sr. The observation is in agreement with the prediction within the errors. The zenith angle dependence of the observed upward through-going muons supports the previous indication of neutrino oscillations made by Kamiokande using sub-…
Using data from both solar and atmospheric neutrinos, Super-Kamiokande has provided fundamental information on neutrino flavor mixing and neutrino mass square differences.
Super-Kamiokande is a 50 kiloton water Cherenkov detector located at the Kamioka Observatory of the Institute for Cosmic Ray Research, University of Tokyo. It was designed to study neutrino oscillations and carry out searches for the decay of the nucleon. The Super-Kamiokande experiment began in 1996 and in the ensuing decade of running has produced extremely important results in the fields of atmospheric and solar neutrino oscillations, along with setting stringent limits on the decay of the nucleon and the existence of dark matter and astrophysical sources of neutrinos. Perhaps most cruciall…
In this talk, I will present a snapshot of key results regarding atmospheric neutrinos, as of the summer of 2002. I will review the evidence for neutrino oscillation, dominated by the large sample from Super-Kamiokande, but supported by confirmation from MACRO and Soudan 2. I will then review some of the more detailed inquiries made using Super-Kamiokande data such as alternative scenarios, three-flavor oscillation, and tau neutrino appearance.
It is said that the finding of the maximum oscillation in neutrino oscillation by Super-Kamiokande is one of the major achievements of the SK. In present paper, we examine the assumption made by Super-Kamiokande Collaboration that the direction of the incident neutrino is approximately the same as that of the produced lepton, which is the cornerstone in their L/E analysis and we find this approximation does not hold even approximately. In the Part 2 of the subsequent paper, we apply the results from Figures 12, 13 and 14 to L/E analysis and conclude that one cannot obtain the maximum oscillati…
From an exposure of 25.5~kiloton-years of the Super-Kamiokande detector, 900 muon-like and 983 electron-like single-ring atmospheric neutrino interactions were detected with momentum $p_e > 100$ MeV/$c$, $p_μ> 200$ MeV/$c$, and with visible energy less than 1.33 GeV. Using a detailed Monte Carlo simulation, the ratio $(μ/e)_{DATA}/(μ/e)_{MC}$ was measured to be $0.61 \pm 0.03(stat.) \pm 0.05(sys.)$, consistent with previous results from the Kamiokande, IMB and Soudan-2 experiments, and smaller than expected from theoretical models of atmospheric neutrino production.
Recent results from a 282 kiloton-year exposure of the Super-Kamiokande detector to atmospheric neutrinos are presented. The data when fit both by themselves and in conjunction with constraints from the T2K and reactor neutrino experiments show a weak, though insignificant, preference for the normal mass hierarchy at the level of ~1 sigma. Searches for evidence of oscillations into a sterile neutrino have resulted in limits on the parameters governing their mixing, |U_mu4}|^2 <0.041 and |U_tau4|^2 < 0.18 at 90% C.L. A similar search for an indication of Lorentz-invariance violating oscillation…
This talk reports the latest indications of an anomaly in the measurements of atmospheric neutrinos. New results from Soudan-2 and Super-Kamiokande provide evidence that the ratio of nu_mu to nu_e interactions is not as expected. High energy Super-Kamiokande data indicates the cause is a deficit of upward-going nu_mu, and the zenith angle dependence of the effect is consistent with neutrino oscillations. Upward-going muon measurements by several detectors are discussed, but in total they provide inconclusive evidence for the anomaly.
In the previous paper (Part~1), we have verified that the SK assumption on the direction does not hold in the analysis of neutrino events occurred inside the SK detector. We have made four possible L/E analyses, L_nu/E_nu, L_nu/E_mu, L_mu/E_nu and L_mu/E_mu. Among four kinds of L/E analyses, we have shown that only L_nu/E_nu analysis can give the signature of maximum oscillations clearly, while the L_mu/E_mu analysis which are really done by Super-Kamiokande Collaboration cannot give the maximum oscillation at all. It is thus concluded that Super-Kamiokande type experiment cannot find the maxi…
A variety of new physics scenarios allow for neutrinos to up-scatter into a heavy neutral lepton state. For a range of couplings and neutrino energies, the heavy neutrino may travel some distance before decaying to visible final states. When both the up-scattering and decay occur within the detector volume, these "double bang" events produce distinctive phenomenology with very low background. In this work, we first consider the current sensitivity at Super-Kamiokande via the atmospheric neutrino flux, and find current data may already provide new constraints. We then examine projected future s…
In this paper we study non-standard neutrino interactions as an example of physics beyond the standard model using atmospheric neutrino data collected during the Super-Kamiokande I(1996-2001) and II(2003-2005) periods. We focus on flavor-changing-neutral-currents (FCNC), which allow neutrino flavor transitions via neutral current interactions, and effects which violate lepton non-universality (NU) and give rise to different neutral-current interaction-amplitudes for different neutrino flavors. We obtain a limit on the FCNC coupling parameter, varepsilon_{mu tau}, |varepsilon_{mu tau}|<1.1 x 10…
The recent results on the oscillation analyses of solar neutrino and the atmospheric neutrino measurements in Super-Kamiokande are presented. Recent status of the detector is also reported.
We consider the oscillations of atmospheric neutrinos in the earth in the three-neutrino scheme with a $Δm^2$ hierarchy and a small admixture of the electron neutrino in the heavy mass eigenstate characterized by the mixing angle $θ_{13}$. We show that for $Δm^2 \simeq (0.5 - 3) \times 10^{-3}$ eV$^2$ indicated by the Super-Kamiokande data and $\sin^2 2θ_{13} \aprle 0.2$, the oscillations of multi-GeV neutrinos in the subdominant $ν_μ \leftrightarrow ν_e$ mode are enhanced by the MSW and parametric resonances. The parametric resonance, which occurs when the neutrinos cross the core of the eart…
We consider a muonphilic axion-like-particle (ALP), denoted as $a$, lighter than twice the muon mass. ALPs of this mass range dominantly decay into a pair of photons, induced by a triangular muon loop. Such light muonphilic ALPs are naturally long-lived. At the atmosphere, the ALPs are copiously produced from charged-meson decays in air showers, such as $π^\pm \to μ^\pm νa$, via the ALP-muon coupling $g_{aμμ}$. After propagating tens of kilometers, the ALPs decay with $a\to γγ$ inside large-volume Cherenkov detectors near the Earth's surface, such as Super-Kamiokande (SK). We find the present …
We present a search for differences in the oscillations of antineutrinos and neutrinos in the Super-Kamiokande -I, -II, and -III atmospheric neutrino sample. Under a two-flavor disappearance model with separate mixing parameters between neutrinos and antineutrinos, we find no evidence for a difference in oscillation parameters. Best fit antineutrino mixing is found to be at (dm2bar, sin2 2 thetabar) = (2.0x10^-3 eV^2, 1.0) and is consistent with the overall Super-K measurement.
We have searched for proton into muon plus neutral kaon using data from a 91.7 kiloton-year exposure of Super-Kamiokande-I, a 49.2 kiloton-year exposure of Super-Kamiokande-II, and a 31.9 kiloton-year exposure of Super-Kamiokande-III. The number of candidate events in the data was consistent with the atmospheric neutrino background expectation and no evidence for proton decay in this mode was found. We set a partial lifetime lower limit of 1.6x10^33 years at the 90% confidence level.
Recent results show that atmospheric $ν_μ$ oscillate with $δm^2 \simeq 3 \times 10^{-3}$ eV$^2$ and $\sin^2{2θ_{atm}} \simeq 1$, and that conversion into $ν_e$ is strongly disfavored. The Super-Kamiokande (SK) collaboration, using a combination of three techniques, reports that their data favor $ν_μ\to ν_τ$ over $ν_μ\to ν_{sterile}$. This distinction is extremely important for both four-neutrino models and cosmology. We propose that neutrino-proton elastic scattering ($ν+ p \to ν+ p$) in water Čerenkov detectors can also distinguish between active and sterile oscillations. This was not previou…
Using 5,326 days of atmospheric neutrino data, a search for atmospheric tau neutrino appearance has been performed in the Super-Kamiokande experiment. Super-Kamiokande measures the tau normalization to be 1.47$\pm$0.32 under the assumption of normal neutrino hierarchy, relative to the expectation of unity with neutrino oscillation. The result excludes the hypothesis of no-tau-appearance with a significance level of 4.6$σ$. The inclusive charged-current tau neutrino cross section averaged by the tau neutrino flux at Super-Kamiokande is measured to be $(0.94\pm0.20)\times 10^{-38}$ cm$^{2}$. The…
This paper summarizes recent (as of SSI-02, in some cases updated in November, 2002) results from the Super-Kamiokande and K2K experiments. The interpretation of Super-Kamiokande results on atmospheric and solar neutrinos provides strong evidence for neutrino oscillations, hence non-zero neutrino mass. While statistics are still limited, K2K data are consistent with Super-Kamiokande results on neutrino oscillations. The effort to reconstruct Super-Kamiokande following a cascade of phototube implosions in November, 2001 is described. Plans for the future are also discussed.
A next generation water Cherenkov detector Hyper-Kamiokande to be built in Japan is described. The main goals of this project include a sensitive measurement of CP violation in neutrino oscillations, a search for proton decay and study of solar, atmospherics and astrophysical neutrinos. Key features of the Hyper-Kamiokande detector are described. The main emphasis is put on large photosensors. The recent progress in the development of near neutrino detectors is also presented.
This conference proceeding discusses new results arising from atmospheric neutrino detection in the Super-Kamiokande and IceCube experiments. Super-Kamiokande has measured atmospheric neutrinos in the energy range of 100 MeV-10 TeV and uses this data set to conclusively measure the east-west effect to 8.0 (6.0) $σ$ for electron (muon) neutrinos. IceCube is ideal for measuring high energy atmospheric neutrinos and has explored how different production channels for atmospheric neutrinos contribute to the total overall observed flux. The measurement is consistent with the conventional spectrum, p…
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.
We investigate the ability of the upcoming Hyper-Kamiokande (Hyper-K) neutrino experiment to detect new physics phenomena beyond the standard, three-massive-neutrinos paradigm; namely the existence of a fourth, sterile neutrino or weaker-than-weak, non-standard neutrino interactions. With both beam-based neutrinos from the Japan Proton Accelerator Research Complex (J-PARC) and atmospheric neutrinos, Hyper-K is capable of exploring new ranges of parameter space in these new-physics scenarios. We find that Hyper-K has comparable capability to the upcoming Deep Underground Neutrino Experiment (DU…
A search for the appearance of tau neutrinos from \mutau oscillations in the atmospheric neutrinos has been performed using 1489.2 days of atmospheric neutrino data from the Super-Kamiokande-I experiment. A best fit tau neutrino appearance signal of 138 $\pm$ 48 (stat.) $^{+15}_{-32}$ (sys.) events is obtained with an expectation of 78 $\pm$ 26 (sys.). The hypothesis of no tau neutrino appearance is disfavored by 2.4 sigma.
We propose the Hyper-Kamiokande (Hyper-K) detector as a next generation un- derground water Cherenkov detector. It will serve as a far detector of a long base- line neutrino oscillation experiment envisioned for the upgraded J-PARC beam, and as a detector capable of observing, far beyond the sensitivity of the Super-Kamiokande (Super-K) detector, proton decays, atmospheric neutrinos, and neutrinos from astro- physical origins. The current baseline design of Hyper-K is based on the highly suc- cessful Super-K detector, taking full advantage of a well-proven technology. Hyper-K consists of two c…
A potential source of high energy neutrinos is the annihilation of Weakly Interacting Massive Particles (WIMPs) collecting in gravitational potential wells such as the centers of the Earth, the Sun, or the Galaxy. A search for such a WIMP annihilation signal using the Super-Kamiokande (Super-K) detector is presented. Super-K observes 1.1 upward through-going muons per day. These events are caused by high energy (typical E_nu ~ 100 GeV) nu_mu interactions in the rock under the detector, and are generally consistent with the expected flux from atmospheric neutrinos. No enhancement of the neutrin…
High-energy neutrinos from SN1987A were searched for using upward-going muons recorded by the Kamiokande-II experiment and the IMB experiment. Between 1987 August 11 and October 20, and from an angular window of 10 degree radius, two upward-going muon events were recorded by Kamiokande-II, and also two events were recorded by IMB. The probability that these upward-going muons were explained by a chance coincidence of atmospheric neutrinos was calculated to be 0.27%. This shows possible evidence of high-energy neutrinos from SN1987A.
This paper presents the recent results from Super-Kamiokande atmospheric neutrinos and from K2K accelerator neutrinos. Both results show the signal of neutrino oscillation, and provide new and precise information of oscillation parameters. The oscillation parameters are constraint to be between 1.5*10^{-3} eV^2 and 3.9*10^{-3} eV^2 for Δm^2 and to be greater than 0.92 for sin^2 2θ.
Many astrophysical models predict a diffuse flux of high-energy neutrinos from active galactic nuclei and other extra-galactic sources. At muon energies above 1 TeV, the upward-going muon flux induced by neutrinos from active galactic nuclei is expected to exceed the flux due to atmospheric neutrinos. We have performed a search for this astrophysical neutrino flux by looking for upward-going muons in the highest energy data sample from the Super-Kamiokande detector using 1679.6 live days of data. We found one extremely high energy upward-going muon event, compared with an expected atmospheric …
It should be regarded that the confirmation of the maximum oscillation in neutrino oscillation through L/E analysis by Super-Kamiokande is a logical consequence of their establishment on the existence of neutrino oscillation through the analysis of the zenith angle distribution for atmospheric neutrino events. In the present paper (Part1) with the computer numerical experiment, we examine the assumption made by Super-Kamiokande Collaboration that the direction of the incident neutrino is approximately the same as that of the produced lepton, which is the cornerstone in their L/E analysis, and …
We have searched for proton decay via $p \rightarrow e^{+} π^{0}$ and $p \rightarrow μ^{+} π^{0}$ using Super-Kamiokande data from April 1996 to March 2015, 0.306 megaton$\cdot$years exposure in total. The atmospheric neutrino background rate in Super-Kamiokande IV is reduced to almost half that of phase I-III by tagging neutrons associated with neutrino interactions. The reach of the proton lifetime is further enhanced by introducing new signal criteria that select the decay of a proton in a hydrogen atom. No candidates were seen in the $p \rightarrow e^{+} π^{0}$ search. Two candidates that …
Neutral current (NC) interactions of atmospheric neutrinos on oxygen form one of the major backgrounds in the search for supernova relic neutrinos with water-based Cherenkov detectors. The NC channel is dominated by neutrino quasi-elastic (NCQE) scattering off nucleons inside $^{16}$O nuclei. In this paper we report the first measurement of NCQE cross section using atmospheric neutrinos at Super-Kamiokande (SK). The measurement used 2,778 live days of SK-IV data with a fiducial volume of 22.5 kiloton water. Within the visible energy window of 7.5-29.5 MeV, we observed $117$ events compared to …
Hyper-Kamiokande has been proposed as a next generation neutrino oscillation experiment capable of observing accelerator, atmospheric, solar and astrophysical neutrinos, as well as possible proton decays, providing a rich scientific program. One of the main goals is the study of CP violation in the lepton sector. The Hyper-Kamiokande detector will be an underground water Cherenkov detector with a fiducial mass of 0.56 million metric tons, approximately 25 times larger than that of Super-Kamiokande. With such a large fiducial mass, the Hyper-Kamiokande detector will need a robust trigger and da…
If the correct interpretation of the Super-Kamiokande atmospheric neutrino data is ν_μ-> ν_τoscillation, the contained data sample should already have more than 10 tau appearance events. We study the challenging task of detecting the tau, focussing on the decay chain τ^\pm -> ρ^\pm -> π^\pm π^0 in events with quasi-elastic tau production. The background level, which is currently quite uncertain because of a lack of relevant neutral current data, can be measured by the near detector in the K2K experiment. Our estimates of the background suggest that it may be possible to detect tau appearance i…
A total of 137 upward stopping muons of minimum energy 1.6 GeV are observed by Super-Kamiokande during 516 detector live days. The measured muon flux is 0.39+/-0.04(stat.)+/-0.02(syst.)x10^{-13}cm^{-2}s^{-1}sr^{-1} compared to an expected flux of 0.73+/-0.16(theo.)x10^{-13}cm^{-2}s^{-1}sr^{-1}. Using our previously-published measurement of the upward through-going muon flux, we calculate the stopping/through-going flux ratio R}, which has less theoretical uncertainty. The measured value of R=0.22+/-0.02(stat.)+/-0.01(syst.) is significantly smaller than the value 0.37^{+0.05}_{-0.04}(theo.) ex…
In the measurement of atmospheric nu_e and nu_mu fluxes, the calculations of the Super Kamiokande group for the distinction between muon-like and electronlike events observed in the water Cerenkov detector have initially assumed a misidentification probability of less than 1 % and later 2 % for the sub-GeV range. In the multi-GeV range, they compared only the observed behaviors of ring patterns of muon and electron events, and claimed a 3 % mis-identification. However, the expressions and the calculation method do not include the fluctuation properties due to the stochastic nature of the proce…
The previously published atmospheric neutrino data did not distinguish whether muon neutrinos were oscillating into tau neutrinos or sterile neutrinos, as both hypotheses fit the data. Using data recorded in 1100 live-days of the Super-Kamiokande detector, we use three complementary data samples to study the difference in zenith angle distribution due to neutral currents and matter effects. We find no evidence favoring sterile neutrinos, and reject the hypothesis at the 99% confidence level. On the other hand, we find that oscillation between muon and tau neutrinos suffices to explain all the …
Neutrino oscillation results from several experiments and sources are discussed. Recent results from solar neutrino measurements by Super-Kamiokande and Borexino, atmospheric neutrino measurements from Super-Kamiokande, and accelerator neutrino measurements by MINOS and OPERA are the main topics of this document.
We present an analysis of atmospheric neutrino data from a 33.0 kiloton-year (535-day) exposure of the Super-Kamiokande detector. The data exhibit a zenith angle dependent deficit of muon neutrinos which is inconsistent with expectations based on calculations of the atmospheric neutrino flux. Experimental biases and uncertainties in the prediction of neutrino fluxes and cross sections are unable to explain our observation. The data are consistent, however, with two-flavor nu_mu <-> nu_tau oscillations with sin^2(2theta)>0.82 and 5x10^-4 < delta m^2 < 6x10^-3 eV^2 at 90% confidence level.
