Stars as Laboratories for Fundamental Physics - MPP Theory Group

Solar Neutrinos 379
Table 10.10. Measured vs. predicted 7 Be and CNO neutrino fluxes (in SNU).
Homestake GALLEX/
( 37 Cl) SAGE ( 71 Ga)
Measurements:
Total 2.55 ± 0.25 77 ± 10
8 B (inferred from 3.15 ± 0.44 7 ± 1
Kamiokande)
pp + pep 0.20 ± 0.01 74 ± 1
(calculated)
Remainder −0.8 ± 0.5 −4 ± 10
BP95 prediction: a
Be 1.24 37.7
CNO 0.48 10.1
Total 1.72 47.8
a Bahcall and Pinsonneault (1995).
ments are correct within the acknowledged uncertainties. If one ignored
Homestake the 99% CL limit would be at 0.5 of the BP95 prediction.
Therefore, the “new solar neutrino problem” consists in the measured
absence of the beryllium neutrino flux. This is a far more serious
deficit than that of the boron flux which has been measured to be a
significant fraction of its expected value, and for which the prediction
is very uncertain anyway.
10.5.3 An Astrophysical Solution
The beryllium problem is very significant because its predicted flux is
closely related to that of the boron flux. A glance at the solar reaction
chains (Fig. 10.2) reveals that both fluxes start with 7 Be,
7 Be + e → 7 Li + ν e ,
7 Be + p → 8 B → 8 Be + e + + ν e . (10.22)
Therefore, the flux ratio of 7 Be/ 8 B neutrinos essentially measures the
branching ratio between the electron and proton capture on 7 Be, admittedly
averaged over slightly different regions of the solar core. The