Solar neutrino event spectra: Tuning SNO to equalize Super-Kamiokande

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Abstract
The Super-Kamiokande (SK) and the Sudbury Neutrino Observatory (SNO) experiments are monitoring the flux of 8B solar neutrinos through the electron energy spectrum from the reactions νe,μ,τ+e−→νe,μ,τ+e− and νe+d→p+p+e−, respectively. We show that the SK detector response to 8B neutrinos in each bin of the electron energy spectrum (above 8 MeV) can be approximated, with good accuracy, by the SNO detector response in an appropriate electron energy range (above 5.1 MeV). For instance, the SK response in the bin [10,10.5] MeV is reproduced (“equalized”) within ∼2% by the SNO response in the range [7.1,11.75] MeV. As a consequence, in the presence of active neutrino oscillations, the SK and SNO event rates in the corresponding energy ranges turn out to be linearly related, for any functional form of the oscillation probability. Such equalization is not spoiled by the possible contribution of hep neutrinos (within current phenomenological limits). In perspective, when the SK and the SNO spectra will both be measured with high accuracy, the SK-SNO equalization can be used to determine the absolute 8B neutrino flux, and to cross-check the (non)observation of spectral deviations in SK and SNO. At present, as an exercise, we use the equalization to “predict” the SNO energy spectrum, on the basis of the current SK data. Finally, we briefly discuss some modifications or limitations of our results in the case of sterile ν oscillations and of relatively large Earth matter effects.
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