Stars as Laboratories for Fundamental Physics - MPP Theory Group

Neutrinos: The Bottom Line 571
Neutrino masses in this general range are also accessible to timeof-flight
measurements. The neutrino burst of SN 1987A has already
provided a limit of m < νe ∼ 20 eV (Sect. 11.3.4), a result which remains
interesting in view of the confusing situation with the tritium β decay
endpoint experiments which seem to be plagued by systematic effects
which cause the appearance of a negative neutrino mass-square
(Sect. 7.1.3). The observation of the prompt ν e burst from a future
galactic SN would allow one to reduce this limit to a few eV. Moreover,
one may well be able to detect or constrain a ν µ or ν τ mass in
the 10−20 eV range, assuming the simultaneous operation of a water
Cherenkov detector such as Superkamiokande and a neutral-current detector
such as the proposed Supernova Burst Observatory (Sect. 11.6).
16.2.2 Oscillations of Solar Neutrinos
Small neutrino masses or rather, small neutrino mass differences can
have dramatic consequences if neutrinos also mix; this is expected in the
present scenario. Neutrino oscillations then lead to the possibility that
a different neutrino flavor is measured in a detector than was produced
in the source. The observed characteristics of the solar neutrino flux
strongly suggest that neutrino oscillations may in fact be occurring. In
terms of the mass difference and mixing angle between ν e and ν µ or ν τ
there remain three solutions which account for the presently available
data from the chlorine (Homestake), gallium (GALLEX and SAGE),
and Cherenkov (Kamiokande) experiments (Tab. 16.1). In view of possible
systematic uncertainties concerning such quantities as the solar
opacities and the p 7 Be cross section the values of the favored mixing
angles can be somewhat different from those shown in Tab. 16.1. However,
the required mass differences remain rather stable against large
nonstandard modifications of the solar model.
Table 16.1. Approximate neutrino parameters which explain all current solar
neutrino observations in the framework of standard solar model assumptions.
Solution ∆m 2 [eV 2 ] sin 2 2θ
Large-angle MSW 2×10 −5 0.6
Nonadiabatic MSW 0.6×10 −5 0.006
Vacuum oscillations 0.8×10 −10 0.8−1