960 research outputs found
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.Comment: 8 pages,3 figures revtex, submitted to PR
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 \nu_\mu \nu_\tau oscillation hypothesis with
\sin^22\theta > 0.4 and 1x10^{-3} < \Delta m^2 < 1x10^{-1} eV^{2} at 90%
confidence level.Comment: 8 pages w/ 3 figures new version contains minor fixes, as it appears
in PR
Measurement of a small atmospheric 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 MeV/, MeV/, and
with visible energy less than 1.33 GeV. Using a detailed Monte Carlo
simulation, the ratio was measured to be , consistent with previous results from the
Kamiokande, IMB and Soudan-2 experiments, and smaller than expected from
theoretical models of atmospheric neutrino production.Comment: 14 pages with 5 figure
Measurement of the CP Violation Parameter sin(2phi_1) in B^0_d Meson Decays
We present a measurement of the Standard Model CP violation parameter
sin(2phi_1) based on a 10.5 fb^{-1} data sample collected at the Upsilon(4S)
resonance with the Belle detector at the KEKB asymmetric e+e- collider. One
neutral B meson is reconstructed in the J/psi K_S, psi(2S) K_S, chi_{c1} K_S,
eta_c K_S, J/psi K_L or J/psi pi^0 CP-eigenstate decay channel and the flavor
of the accompanying B meson is identified from its charged particle decay
products. From the asymmetry in the distribution of the time interval between
the two B-meson decay points, we determine sin(2phi_1) = 0.58 +0.32-0.34 (stat)
+0.09-0.10 (syst).Comment: LaTex, 13 pages, 3 figures, submitted to P.R.
Observation of Large CP Violation in the Neutral B Meson System
We present a measurement of the Standard Model CP violation parameter sin
2phi_1 based on a 29.1 fb^{-1} data sample collected at the Upsilon(4S)
resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider.
One neutral B meson is fully reconstructed as a J/psi Ks, psi(2S) Ks, chi_c1
Ks, eta_c Ks, J/psi K_L or J/psi K^{*0} decay and the flavor of the
accompanying B meson is identified from its decay products. From the asymmetry
in the distribution of the time intervals between the two B meson decay points,
we determine sin 2phi_1 = 0.99 +- 0.14(stat) +- 0.06(syst). We conclude that we
have observed CP violation in the neutral B meson system.Comment: 4 figures, to appear in Phys. Rev. Letter
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.Comment: 9 pages (two-column) with 4 figures. Small corrections to Eqn.4 and
Fig.3. Final version to appear in PR
Measurement of radon concentrations at Super-Kamiokande
Radioactivity from radon is a major background for observing solar neutrinos
at Super-Kamiokande. In this paper, we describe the measurement of radon
concentrations at Super-Kamiokande, the method of radon reduction, and the
radon monitoring system. The measurement shows that the current low-energy
event rate between 5.0 MeV and 6.5 MeV implies a radon concentration in the
Super-Kamiokande water of less than 1.4 mBq/m.Comment: 11 pages, 4 figure
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.Comment: 24 pages, 16 figures, Submitted to NIM
Constraints on neutrino oscillation parameters from the measurement of day-night solar neutrino fluxes at Super-Kamiokande
A search for day-night variations in the solar neutrino flux resulting from
neutrino oscillations has been carried out using the 504 day sample of solar
neutrino data obtained at Super-Kamiokande. The absence of a significant
day-night variation has set an absolute flux independent exclusion region in
the two neutrino oscillation parameter space.Comment: 11 pages, 3 figures, submitted to PRL, single-spacin
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