Development of a Liquid Scintillator and of Data ... - Borexino - Infn

Neutrino-Oscillation Solutions to the Solar Neutrino Problem
1.3 The Solar Neutrino Puzzle
A global analysis of the Homestake, SAGE, GALLEX+GNO and Super-Kamiokande results
leaves only a few allowed regions in the ¡Ñ ØÒ plane. These are shown in fig. 1.6
[Bah01b]. The choice of the variable ØÒ rather than ×Ò allows to include also mixing
angles larger than (the so-called dark side). The no-oscillation hypothesis is excluded at
99.7 % C.L. ( ).
The latest results from Super-Kamiokande [Fuk01] and SNO [Ahm01] disfavour the possibility
of oscillations to sterile neutrinos and prefer the solutions with large mixing angles
(×Ò ), e.g. [Fog01, Bah01b]. The best fit values for the global analysis including
the SNO results are listed in table 1.3 and shown in fig. 1.7 [Bah01b]. The CC measurement
by SNO has not changed qualitatively the globally allowed solution space for solar neutrinos,
though it has provided convincing evidence for neutrino oscillations into active neutrinos. I
will show in the next chapter, that the BOREXINO experiment has the potential to distinguish
between the currently allowed oscillation scenarios.
Figure 1.6: Global analysis of the Homestake, SAGE, GALLEX/GNO and Super-Kamiokande
results, taking into account the total rates, and the B energy spectrum measured by Super-
Kamiokande separately during the day and during the night as well as the theoretical neutrino
fluxes according to BP00. The MSW solutions are known as ”small mixing angle”, ”large mixing
angle” and ”low” solution, respectively. The contours correspond to 90 %, 95 %, 99 % and
99.73 % C.L. relative to each of the best-fit solutions (marked with black circles). Taken from
[Bah01b].
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