Stars as Laboratories for Fundamental Physics - MPP Theory Group

Neutrino Oscillations 291
Fig. 8.6. Limits on neutrino masses and mixing angles from atmospheric
neutrinos. (a) The shaded area is the range of masses and mixing angles
required to explain the ν e /ν µ anomaly at Kamiokande (Fukuda et al. 1994);
the star marks the best-fit value for the mixing parameters. The hatched
areas are excluded by: (b) ν e /ν µ ratio at Fréjus (Fréjus Collaboration 1990,
1995; Daum 1994). (c) Absolute rate and (d) stopping fraction of upward going
muons at IMB (Becker-Szendy et al. 1992). Also shown are the excluded
areas from the experimental limits of Fig. 8.5.
and 13000 km are available. 48 The energy spectrum and absolute normalization
of the flux must be determined by calculations and thus is
probably uncertain to within about ±30% while the ν e /ν µ flavor ratio
is likely known to within, say, ±5%.
Several underground proton decay experiments have reported measurements
of atmospheric neutrinos. The Fréjus detector (an iron
calorimeter) saw the expected ν e /ν µ flavor ratio and thereby excluded
the range of masses and mixing angles marked b in Fig. 8.6 for ν e -ν µ
and ν µ -ν τ oscillations (Fréjus Collaboration 1990, 1995; Daum 1994).
Instead of measuring the neutrinos directly one may also study the
flux of secondary muons produced by interactions in the rock surround-
48 The effect of matter must be included for ν e -ν µ atmospheric neutrino oscillations.
For a recent detailed analysis see Akhmedov, Lipari, and Lusignoli (1993).