Stars as Laboratories for Fundamental Physics - MPP Theory Group

376 Chapter 10
and for the central 14 ◦ ×14 ◦ which is the region most significant for the
neutrino flight path to us. The disk-centered magnetic-field cycle lags
full-disk indicators by about 1 y. Oakley et al. (1994) found a significance
level of 0.001% for an anticorrelation between the Homestake rate
and the disk-centered magnetic flux. Including the flux from increasingly
higher latitudes reduced the significance level of the correlation.
With only high-latitude magnetic information the correlation was lost.
Another test of time variation is a comparison as in Fig. 10.7 between
the expected and measured distribution of argon production
rates. A time variation would broaden the measured distribution (black
histogram) relative to the expectation for a constant neutrino flux
(shaded histogram). A certain degree of broadening is certainly compatible
with Fig. 10.7, but a precise statistical analysis does not seem
to be available at the present time. At any rate, the rank-ordering result
does not specify the amplitude of a time varying signal relative to a
constant base rate while the width of the distribution in Fig. 10.7 would
be sensitive mostly to this amplitude. Therefore, the two methods yield
rather different information concerning a possible time variation.
The gallium experiments have not been running long enough to say
much about a time variation on the time scale of several years. Also,
there does not seem to be a significant time variation in the Kamiokande
data between 1987 and 1992 which covers a large fraction of the current
solar cycle No. 22. Notably, there is no apparent (anti)correlation
with sunspot number (Suzuki 1993). However, a correlation with diskcentered
magnetic indicators may yield a different result—according to
the analysis of Oakley et al. (1994) the use of a disk-centered indicator
with its inherent time-lag relative to full-disk spot counts is crucial for
the strong anticorrelation at Homestake.
The constancy of the Kamiokande rate, if confirmed over a more
extended period, severely limits a conjecture that the nuclear energy
generating region in the Sun was not constant (e.g. Raychaudhuri 1971,
1986). Because the Kamiokande detector is mostly sensitive to the
boron neutrinos with their extreme sensitivity to temperature, they
would be expected to show the most extreme time variations if the
solar cycle was caused by processes in the deep interior rather than by
dynamo action in the convective surface layers.
10.4.4 Summary
There is no indication for a day-night variation of the solar neutrino
flux at Kamiokande and none for a seasonal variation at Kamiokande,