Solar neutrino measurements in Super-Kamiokande-I

TL;DR

This work delivers high-statistics measurements of $^8$B solar neutrinos with SK--I (1496 days), extracting flux, energy spectrum, and time variations via neutrino–electron scattering. It employs a comprehensive detector calibration, meticulous background suppression, and a robust oscillation analysis (zenith-spectrum and unbinned time variation) to constrain two-neutrino mixing within MSW, with a best-fit in the Large Mixing Angle region. The results, including a measured flux of $(2.35 \\pm 0.02_{stat} \\pm 0.08_{sys}) imes 10^{6} \, ext{cm}^{-2} ext{s}^{-1}$ and a day/night asymmetry around a few percent, are consistent with no spectral distortion and favor the LMA solution. When combined with SNO and KamLAND data, the paper strengthens the LMA interpretation and tightens oscillation-parameter uncertainties, highlighting the impact of solar-neutrino data on neutrino physics and standard solar-model tests.

Abstract

The details of Super--Kamiokande--I's solar neutrino analysis are given. Solar neutrino measurement in Super--Kamiokande is a high statistics collection of $^8$B solar neutrinos via neutrino-electron scattering. The analysis method and results of the 1496 day data sample are presented. The final oscillation results for the data are also presented.

Figures (57)

• Figure 1: Coordinates of the Super--Kamiokande detector. The Z-axis is defined as the upward direction, pointing away from the center of the earth.
• Figure 2: (a) The average dark noise rate of the PMT's used in SK--I. The dashed lines show the acceptable range for use in the solar neutrino analysis. (b) Number of dead PMT's in SK--I. Note that sometimes repairs were possible, usually involving the replacement of broken high voltage supplies, leading to sudden drops in the number of dead PMT's.
• Figure 3: Trigger efficiency as a function of energy. The left plot shows the efficiency as a function of reconstructed energy (see Section \ref{['sec:ene']} for the details of reconstructed energy). The May 1997 LE triggers (black circles with black line) and SLE triggers (white circles with red line) were calculated using a Ni(n,$\gamma$)Ni gamma source, while the SLE triggers on September 1999 (triangles with green line) and September 2000 (stars with blue line) were calculated using $^{16}$N events from a DT generator. The right plot shows the efficiency as a function of true electron total energy obtained by a Monte Carlo simulation. Identically colored lines represent the same calibration data samples in both plots.
• Figure 4: (a) Input distributions of $^8$B (solid) and hep (dashed) solar neutrino energies. (b) The cross section of the interaction for $\nu_e$ (solid line) and $\nu_{\mu,\tau}$ (dashed line) with electrons as a function of neutrino energy. (c) The spectrum of recoil electrons scattered by $^8$B and hep solar neutrinos.
• Figure 5: Wavelength dependence of the water parameter coefficients: absorption (solid), Rayleigh scattering (dashed) and Mie scattering (dotted). The absorption coefficient is also a function of water transparency. The filled region shows the range of this parameter as water transparency is changed, where the two solid lines define the SK--I minimum (73 meter) and maximum (98 meter) values.