Enhancing the Seasonal Variation Effect in the Case of the Vacuum Oscillation Solution of the Solar Neutrino Problem

We study in detail the threshold energy dependence of the seasonal variation effect in the energy integrated solar neutrino signal of the Super-Kamiokande detector in the case of the νe ↔ νμ,τ vacuum oscillation (VO) solution of the solar neutrino problem. We show, in particular, that for the values of ∆m2 and sin 2θ from the VO solution region, the predicted time and threshold e− energy (Te,Th) dependence of the event rate factorize to a high degree of accuracy. As a consequence, the VO generated seasonal variation asymmetry is given by the product of an time-independent function of Te,Th and the standard geometrical asymmetry. For any given ∆m2 and sin 2θ from the VO solution region there exists at least one value of Te,Th from the interval (5− 11) MeV, for which the seasonal variation effect in the solar neutrino sample of events, formed by recoil electrons with kinetic energy Te ≥ Te,Th, is either maximal or very close to the maximal; it can vary dramatically with Te,Th. One can effectively search for the VO induced seasonal effect by forming a set of samples of solar neutrino events, corresponding to a sufficiently large number of different values of Te,Th from the indicated interval and by measuring the seasonal variation in each of these samples. Predictions for the magnitude of the seasonal effect in such samples are given for a large set of representative values of ∆m2 and sin 2θ from the VO solution region. ∗Also at: Institute of Nuclear Research and Nuclear Energy, Bulgarian Academy of Sciences, BG–1784 Sofia, Bulgaria.