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Kamiokande Collaboration

Publications and source records attributed to Kamiokande Collaboration.

90 records · Page 5Linked to original sources
arXiv2001

Solar 8B and hep Neutrino Measurements from 1258 Days of Super-Kamiokande Data

Solar neutrino measurements from 1258 days of data from the Super-Kamiokande detector are presented. The measurements are based on recoil electrons in the energy range 5.0-20.0MeV. The measured solar neutrino flux is 2.32 +- 0.03(stat.) +0.08-0.07(sys.)*10^6cm^{-2}s^{-1}, which is 45.1+-0.5(stat.)+1.6-1.4(sys.)% of that predicted by the BP2000 SSM. The day vs night flux asymmetry is 0.033+-0.022(stat.)+0.013-0.012(sys.). The recoil electron energy spectrum is consistent with no spectral distortion (χ^2/d.o.f. = 19.0/18). The seasonal variation of the flux is consistent with that expected from the eccentricity of the Earth's orbit (χ^2/d.o.f. = 3.7/7). For the hep neutrino flux, we set a 90% C.L. upper limit of 40 *10^3cm^{-2}s^{-1}, which is 4.3 times the BP2000 SSM prediction.

hep-ex↗
arXiv2001

Constraints on Neutrino Oscillations Using 1258 Days of Super-Kamiokande Solar Neutrino Data

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 flux from 1258 days of neutrino-electron scattering data in Super-Kamiokande. The absence of significant zenith angle variation and spectrum distortion places strong constraints on neutrino mixing and mass difference in a flux-independent way. Using the Super-Kamiokande flux measurement in addition, two allowed regions at large mixing are found.

hep-ex↗
arXiv2001

16-N as a calibration source for Super-Kamiokande

The decay of 16-N is used to cross check the absolute energy scale calibration for solar neutrinos established by the electron linear accelerator (LINAC). A deuterium-tritium neutron generator was employed to create 16-N via the (n,p) reaction on 16-O in the water of the detector. This technique is isotropic and has different systematic uncertainties than the LINAC. The results from this high statistics data sample agree with the absolute energy scale of the LINAC to better than 1%. A natural source of 16-N from the capture of mu^- on 16-O, which is collected as a background to the solar neutrino analysis, is also discussed.

hep-ex↗
arXiv2000

Tau Neutrinos Favored over Sterile Neutrinos in Atmospheric Muon Neutrino Oscillations

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 results in hand.

hep-ex↗
arXiv2000

Searches for astronomical neutrino sources and WIMPs with Super-Kamiokande

Searches for astronomical neutrino sources and weakly interactive massive particles (WIMPs) using the Super-Kamiokande detector have been performed. We select the neutrino-induced upward muon events for the first 4 years, which is already the world largest data sample, and look for statistically significant excesses compared to the atmospheric neutrino background. No excess has been found so far. Limits of upward muon flux from various potential sources are obtained. Also limits of upward muon flux due to annihilations of WIMPs in the Earth core, the Sun and the Galactic center are obtained as a function of WIMP masses.

astro-ph↗
arXiv1999

Neutrino-induced upward stopping muons in Super-Kamiokande

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.) expected using the best theoretical information (the probability that the measured R is a statistical fluctuation below the expected value is 0.39%). A simultaneous fitting to zenith angle distributions of upward stopping and through-going muons gives a result which is consistent with the hypothesis of neutrino oscillations with the parameters sin^2 2θ>0.7 and 1.5x10^{-3} < Δm^2 < 1.5x10^{-2} eV^2 at 90% confidence level, providing a confirmation of the observation of neutrino oscillations by Super-Kamiokande using the contained atmospheric neutrino events.

hep-ex↗
arXiv1999

Search for proton decay through p->\barν K^+ in a large water Cherenkov detector

We present results of a search for proton decays, $p \to \barν K^+$, using data from a 33 kton$\cdot$year exposure of the Super-Kamiokande detector. Two decay modes of the kaon, $K^+ \to μ^+ ν_μ$ and $K^+ \to π^+ π^0$, were studied. The data were consistent with the background expected from atmospheric neutrinos; therefore a lower limit on the partial lifetime of the proton $τ/ B(p \to \barν K^+)$ was found to be $6.7 \times 10^{32}$ years at 90% confidence level.

hep-ex↗
arXiv1999

Measurement of the flux and zenith-angle distribution of upward through-going muons by Super-Kamiokande

A total of 614 upward through-going muons of minimum energy 1.6 GeV are observed by Super-Kamiokande during 537 detector live days. The measured muon flux is 1.74+/-0.07(stat.)+/-0.02(sys.)x10^{-13}cm^{-2}s^{-1}sr^{-1} compared to an expected flux of 1.97+/-0.44(theo.)x10^{-13}cm^{-2}s^{-1}sr^{-1}. The absolute measured flux is in agreement with the prediction within the errors. However, the zenith angle dependence of the observed upward through-going muon flux does not agree with no-oscillation predictions. The observed distortion in shape is consistent with the ν_μ<-> ν_τoscillation hypothesis with \sin^22θ> 0.4 and 1x10^{-3} < Δm^2 < 1x10^{-1} eV^{2} at 90% confidence level.

hep-ex↗
arXiv1999

Observation of the east-west anisotropy of the atmospheric neutrino flux

The east-west anisotropy, caused by the deflection of primary cosmic rays in the Earth's magnetic field, is observed for the first time in the flux of atmospheric neutrinos. Using a 45 kt-year exposure of the Super-Kamiokande detector, 552 e-like and 633 mu-like horizontally-going events are selected in the momentum range between 400 and 3000 MeV/c. The azimuthal distribution of e-like and mu-like events agrees with the expectation from atmospheric neutrino flux calculations that account for the geomagnetic field, verifying that the geomagnetic field effects in the production of atmospheric neutrinos in the GeV energy range are well understood.

astro-ph↗
arXiv1998

Evidence for oscillation of atmospheric neutrinos

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.

hep-ex↗
arXiv1998

Measurements of the Solar Neutrino Flux from Super-Kamiokande's First 300 Days

The first results of the solar neutrino flux measurement from Super-Kamiokande are presented. The results shown here are obtained from data taken between the 31st of May, 1996, and the 23rd of June, 1997. Using our measurement of recoil electrons with energies above 6.5 MeV, we infer the total flux of 8B solar neutrinos to be 2.42+-0.06(stat.)+0.10-0.07(syst.)*10^6/cm^2/s. This result is consistent with the Kamiokande measurement and is 36% of the flux predicted by the BP95 solar model. The flux is also measured in 1.5 month subsets and shown to be consistent with a constant rate.

hep-ex↗
arXiv1998

Calibration of Super-Kamiokande Using an Electron Linac

In order to calibrate the Super-Kamiokande experiment for solar neutrino measurements, a linear accelerator (LINAC) for electrons was installed at the detector. LINAC data were taken at various positions in the detector volume, tracking the detector response in the variables relevant to solar neutrino analysis. In particular, the absolute energy scale is now known with less than 1 percent uncertainty.

hep-ex↗
arXiv1998

Study of the atmospheric neutrino flux in the multi-GeV energy range

The flavor ratio of the atmospheric neutrino flux and its zenith angle dependence have been studied in the multi-GeV energy range using an exposure of 25.5 kiloton-years of the Super-Kamiokande detector. By comparing the data to a detailed Monte Carlo simulation, the ratio $(μ/e)_{DATA}/(μ/e)_{MC}$ was measured to be $0.66\pm0.06(stat.)\pm0.08(sys.)$. In addition, a strong distortion in the shape of the $μ$-like event zenith angle distribution was observed. The ratio of the number of upward to downward $μ$-like events was found to be 0.52$^{+0.07}_{-0.06}(stat.)\pm0.01(sys.)$, with an expected value of $0.98\pm0.03(stat.)\pm0.02(sys.)$, while the same ratio for the $e$-like events was consistent with unity.

hep-ex↗
arXiv1998

Measurement of the flux and zenith-angle distribution of upward through-going muons in Kamiokande II+III

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- and multi-GeV atmospheric neutrino events.

hep-ex↗
arXiv1998

Search for Proton Decay via p -> e+ pi0 in a Large Water Cherenkov Detector

We have searched for proton decay via p -> e+ pi0 using data from a 25.5 kton-year exposure of the Super-Kamiokande detector. We find no candidate events with an expected background induced by atmospheric neutrinos of 0.1 events. From these data, we set a lower limit on the partial lifetime of the proton to be 1.6E33 years at a 90% confidence level.

hep-ex↗
arXiv1998

Measurement of a small atmospheric $ν_μ/ν_e$ ratio

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.

hep-ex↗
arXiv1997

Underground Muons in Super-KAMIOKANDE

The largest underground neutrino observatory, Super-Kamiokande, located near Kamioka, Japan has been collecting data since April 1996. It is located at a depth of roughly 2.7 kmwe in a zinc mine under a mountain, and has an effective area for detecting entering-stopping and through-going muons of about $1238 m^2$ for muons of $>1.7 GeV$. These events are collected at a rate of 1.5 per day from the lower hemisphere of arrival directions, with 2.5 muons per second in the downgoing direction. We report preliminary results from 229 live days analyzed so far with respect to zenith angle variation of the upcoming muons. These results do not yet have enough statistical weight to discriminate between the favored hypothesis for muon neutrino oscillations and no-oscillations. We report on the search for astrophysical sources of neutrinos and high energy neutrino fluxes from the sun and earth center, as might arise from WIMP annihilations. None are found. We also present a topographical map of the overburden made from the downgoing muons. The detector is performing well, and with several years of data we should be able to make significant progress in this area.

astro-ph↗