Stars as Laboratories for Fundamental Physics - MPP Theory Group

380 Chapter 10
boron and beryllium fluxes respond very differently to a modification
of the solar central temperature (Eq. 10.5). Because the boron flux
has been measured, even at a reduced strength, it is not possible to
explain the missing beryllium neutrinos by a low solar temperature unless
one is willing to contemplate simultaneously an extremely reduced
temperature and an extremely enhanced S 17 factor.
Many authors 57 have recently investigated the question of the significance
of the solar neutrino problem, and if it can be solved by a
plausible, or even implausible, combination of erroneous nuclear cross
sections, solar opacities, and so forth. The consensus is that an astrophysical
solution is not possible, even if one ignores part of the experimental
data. There is no obvious uncertain input quantity into
solar modelling or the flux predictions that could be tuned to obtain
the measured fluxes. Therefore, something mysterious is wrong with
the calculation of the solar neutrino fluxes and/or the solar neutrino
experiments.
However, if our understanding of the solar neutrino source and of
the detection experiments is not totally wrong, an attractive alternative
is to contemplate the option that something happens to the neutrinos
as they propagate from the solar core to us.
10.6 Neutrino Oscillations
10.6.1 Which Data to Use
The idea to test the hypothesis of neutrino oscillations by means of
the solar neutrino flux goes back to Pontecorvo (1957, 1958, 1967) and
Maki, Nakagawa, and Sakata (1962). After the first measurements
in 1968 it was revived by Gribov and Pontecorvo (1969) as well as
Bahcall and Frautschi (1969). If some of the ν e ’s produced in the Sun
transformed into ν e ’s, into other sequential neutrinos (ν µ , ν τ ), or into
hypothetical sterile states ν s , the measurable flux at Earth would be
depleted. Even the Kamiokande detector which responds to ν µ and ν τ
because of the possibility of neutral-current ν-e scattering would show
a reduced flux because of the smaller cross section. The measured flux
57 These include Bludman, Kennedy, and Langacker (1992a,b); Bludman et al.
(1993); Bahcall and Bethe (1993); Castellani, Degl’Innocenti, and Fiorentini
(1993); Castellani et al. (1994b); Hata, Bludman, and Langacker (1994); Shi and
Schramm (1994); Shi, Schramm, and Dearborn (1994); Kwong and Rosen (1994);
Bahcall (1994b); Berezinski (1994); Degl’Innocenti, Fiorentini, and Lissia (1995);
Parke (1995); Hata and Haxton (1995); Haxton (1995).