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Next: Implications Up: Solar Neutrinos (Erice 1994) Previous: Mikheyev-Smirnov-Wolfenstein (MSW)

The Future

In the future one will want to verify or falsify that MSW is occurring, or choose some other possibility. Assuming that MSW is correct, one will want to find the unique solution for the parameters and tell whether the oscillations are into active or sterile neutrinos. Not only will the gallium experiments have better statistics and calibrations but, in addition, there will be a new generation of experiments. For example, the Sudbury Neutrino Observatory (SNO), which is a heavy water experiment being built by a Canadian-American collaboration in Canada, will have many new capabilities. It will be able to measure charged current reactions from deuterium,

 

It will also be able to measure the neutral current reaction,

 

and will observe electron scattering

 

with both charged and neutral current amplitudes. The ratio of neutral current to charged current rates can be measured directly or by comparing the charged current rate with the electron scattering results from SNO or from the Super-Kamiokande experiment (a large water Cerenkov experiment being built in Japan). If different from the weak interaction expectations, the ratio will clearly indicate neutrino oscillations, either vacuum or MSW. Therefore, one should be able to distinguish new neutrino physicsgif from astrophysical solutions in a way independent of astrophysical uncertainties. Assuming this is observed, one will be able to use the neutral current events to calibrate the initial flux and determine the core temperature. (Or, more accurately, a combination of the core temperature and .) In addition, the SNO experiment will be sensitive to spectral distortions. These are expected to be significant for the non-adiabatic MSW solution, but not for the large angle, and are essentially free of astrophysical uncertainties. Vacuum oscillation solutions would also give large spectral distortions. This is illustrated in Figure 13. The Super-Kamiokande experiment will have high statistics for electron scattering and should also be able to observe spectrum distortions.

  
Figure: Expected spectrum distortions for the MSW non-adiabatic and various vacuum oscillation experiments, with expected uncertainties. The large angle solution exhibits no significant distortions and is similar to an astrophysical solution. From [42,49,50].

  
Figure: Expected seasonal variations for various vacuum oscillation solutions in the SNO, Super-Kamiokande, and BOREXINO experiments. From [42,49,50].

Yet another probe that is free of astrophysical uncertainties is that the large angle solution is expected to yield a significant day/night asymmetry in the SNO and Super-Kamiokande experiments. This may even be observable in Kamiokande III. Not only are there the day/night effects expected from MSW, but one expects large seasonal variations for vacuum oscillations, as indicated in Figure 14.

Another experiment, BOREXINO in the Gran Sasso Laboratory in Italy, will be sensitive to the line. This is especially interesting because there is every indication that this is where the dominant suppression occurs. Furthermore, other explanations of the solar neutrino problem, such as large magnetic moments [44], would imply interesting consequences for the line.

Altogether, these experiments should be able to establish or refute the MSW solution, determine the parameters, and probe alternatives precisely. Whatever happens, one is still interested in the neutrinos not only for particle physics but also for astrophysics. Fortunately, even if MSW is going on it should be possible to establish it and constrain the parameters from the methods described above, with little uncertainty from astrophysics or nuclear physics. In fact, there should be enough data not only to determine the MSW parameters but also to determine the initial pp, , and flux components in a model independent way, much as was described in Section 4.2 for astrophysical solutions without MSW [10]. For this program one will need, in addition to SNO and Super-Kamiokande, the BOREXINO measurement of the line. That is because MSW can lead to an almost total suppression of the flux. However, BOREXINO will have a neutral current sensitivity to the converted neutrinos at about 20% of the efficiency, yielding a measure of the initial flux. In addition to the model independent studies, one can determine the parameters of the standard solar models, such as and , simultaneously with and . The projected sensitivity is shown in Figure 15.

  
Figure: Projected uncertainties in the simultaneous determination of , , and the MSW parameters, assuming future experiments. From [10].



next up previous
Next: Implications Up: Solar Neutrinos (Erice 1994) Previous: Mikheyev-Smirnov-Wolfenstein (MSW)




Mon Nov 27 19:39:39 EST 1995