Stars as Laboratories for Fundamental Physics - MPP Theory Group

Solar Neutrinos 385
The allowed ranges from the different experiments as well as the
combined allowed range are shown in Fig. 10.19 according to the analysis
of Hata and Haxton (1995). They used the Bahcall and Pinsonneault
(1995) solar model with helium and metal diffusion and its uncertainties.
The black areas represent the 95% CL allowed range if one
includes all the experimental information quoted in Sect. 10.3, including
the GALLEX source experiment. The center of the allowed area
for the “Large-Angle Solution” is roughly
sin 2 2θ = 0.6,
∆m 2 ν = 2×10 −5 eV 2 , (10.24)
while for the “Nonadiabatic Solution” or “Small-Angle Solution” it is
sin 2 2θ = 0.6×10 −2 ,
∆m 2 ν = 0.6×10 −5 eV 2 . (10.25)
Both cases amount essentially to the same neutrino mass-square difference.
Other recent and very detailed analyses are by Fiorentini et al.
(1994), Hata and Langacker (1994), and Gates, Krauss, and White
(1995) who find similar results. In detail, their confidence contours
differ because they used other solar models or a different statistical
analysis.
A certain region of parameters (dotted area in Fig. 10.19) can be
excluded by the absence of a day/night difference in the Kamiokande
counting rates which are expected for the matter-induced back oscillations
into ν e when the neutrino path intersects with part of the Earth
at night. (Even though the detector is deep underground in a mine
the overburden of material during daytime is negligible.) The excluded
range of masses and mixing angles is independent of solar modelling as
it is based only on the relative day/night counting rates.
Except for the Kamiokande day/night exclusion region one should
be careful at taking the confidence contours in a plot like Fig. 10.19 too
seriously. The solar model uncertainties are dominated by systematic
effects which cannot be quantified in a statistically objective sense. One
of the main uncertain input parameters is the astrophysical S-factor
for the reaction p 7 Be → 8 B γ. Speculating that all or most of the
missing boron neutrino flux is accounted for by a low S 17 has the effect
of reducing the best-fit sin 2 2θ of the small-angle solution by about a
factor of 3 while the large-angle solution disappears, at least in the
analysis of Krastev and Smirnov (1994). The best-fit ∆m 2 , however,