Stars as Laboratories for Fundamental Physics - MPP Theory Group

Solar Neutrinos 377
GALLEX, or Homestake. The Homestake argon production rate appears
to be strongly anticorrelated with solar disk-centered indicators
of magnetic activity, with no evidence for a long-term variation at
Kamiokande. However, the period covered there (1987−1992) may be
too short, and the Kamiokande rate has not been correlated with diskcentered
indicators. No homogeneous analysis of both Kamiokande and
Homestake data relative to solar activity exists at the present time.
It is very difficult to judge what the apparent Homestake anticorrelation
with solar activity means. Is there an unrecognized background
which correlates with solar activity such as cosmic rays Is there a
long-term drift in some aspect of the experiment which then naturally
correlates with other causally unrelated long-term varying phenomena
such as solar activity Is it all some statistical fluke Or is it an indication
of nonstandard neutrino properties, notably magnetic dipole moments
which spin precess in the solar magnetic field into sterile states
This latter possibility will be elaborated further in Sect. 10.7.
10.5 Neutrino Flux Deficits
10.5.1 Boron Flux
Even if one ignores for the moment a possible time variation of the
Homestake neutrino measurements there remain several “solar neutrino
problems.” All of the solar neutrino flux measurements discussed in
Sect. 10.3 exhibit a deficit relative to theoretical predictions. The simplest
case to interpret is that of Kamiokande because it is sensitive only
to the boron flux. In this case the most uncertain input parameter is
the cross section for the reaction p 7 Be → 8 Bγ which enters the flux prediction
as a multiplicative factor, independently of other details of solar
modelling. As discussed in Sect. 10.2.3, the astrophysical S-factor for
this reaction depends on theoretical extrapolations to low energies of
experimental data which themselves seem to exhibit relatively large systematic
uncertainties. Therefore, one may turn the argument around
and consider the solar neutrino flux measurement at Kamiokande as
another determination of S 17 (0).
According to Eq. (10.20) the measured flux is 2.89 × (1 ± 0.14) in
units of 10 6 cm −2 s −1 while the prediction is 4.4×(1±0.21)×S 17 (0)/22.4
for TL93 (Turck-Chièze and Lopes 1993) where S 17 is understood in
units of eV b. For the BP95 (Bahcall and Pinsonneault 1995) it is
6.6 × (1 ± 0.15) × S 17 (0)/22.4 where I have used an average symmetric