Study of Solar Neutrinos at Super Kamiokande
Yusuke Koshio
University of Tokyo
July 1998
A thesis for the degree of PhD
Abstract:
Super-Kamiokande started taking data on the 1st of April in 1996.
The data used for the analysis of solar neutrinos in this paper was obtained
from the 31st of May, 1996 to the 23rd of June, 1997 and the total live time
is 297.4 days. The energy threshold is 6.5MeV and the fiducial volume is
22.5 ktons.
The observed $^8$B solar neutrino flux in Super-Kamiokande is
\[
2.42 \quad ^{+0.06}_{-0.06} (stat.) \quad ^{+0.13}_{-0.09} (sys.)
\quad [\times 10^6/cm^2/sec].
\]
The observed flux is smaller than the predicted by Bahcall and Pinsonneault
(BP95). The ratio is
\[
\frac{Data}{SSM(BP95)} = 0.365 \quad ^{+0.010}_{-0.010} (stat.)
\quad ^{+0.019}_{-0.013} (sys.).
\]
Comparing this deficit with the result of the Homestake experiment,
the solar neutrino problem is difficult to explain by changing solar models
but is more naturally explained by neutrino oscillations.
The solar neutrino flux of daytime and night-time agrees within the
experimental errors and the result restricts the allowed neutrino oscillation
parameters of the MSW effect. If we assume the large angle solutions to the
solar neutrino problem, according to the MSW effect, neutrinos would regenerate
through the earth. This analysis, which is independent of the solar models,
excludes half of the large angle region which was obtained from the
model-dependent analysis of the combined results from the past experiments.
Within five years, the data sample from Super-Kamiokande should be large enough
to study the whole large angle region.
Seasonal flux differences were not seen but currently, the statistical
relevance of the data sample is insufficient. No energy distortion was found
within the errors. For the analysis of the energy spectrum, more statistics and
smaller systematic errors are needed.
Paper:
PDF file (5.5 Mbyte)
KOSHIO, Yusuke (ICRR, Kamioka)