Atmospheric neutrinos at Super-Kamiokande and parametric resonance in neutrino oscillations

摘要

We consider the oscillations of atmospheric neutrinos in the earth in the three-neutrino scheme with a (Delta)m(sup 2) hierarchy and a small admixture of the electron neutrino in the heavy mass eigenstate characterized by the mixing angle theta(sub 13). We show that for (Delta)m(sup 2) (approx-equal) (0.5-3) x 10 to the -3 power eV(sup 2) indicated by the Super-Kamiokande data and sin(sup 2) 2(theta)(sub 13) < or approx. 0.2, the oscillations of multi-GeV neutrinos in the subdominant nu(sub mu) (r-reversible) nu(sub e) mode are enhanced by the MSW and parametric resonances. The parametric resonance, which occurs when the neutrinos cross the core of the earth, dominated for (Delta)m(sup 2) (approx-equal) (1-2) x 10 to the -3 power V(sup 2), sin(sup 2) 2(theta)(sub 13) < or approx. 0.06. The resonance matter effects lead to an observable excess of the e-like events with a specific zenith angle dependence even for small theta (sub 13). The up-down asymmetry of the multi GeV elike events can reach 15% for vertical-bar cos(Theta)(sub e) (vertical-bar) > 0.2 and up to 30% for (vertical-bar) cos(Theta)(sub e) (vertical-bar) > 0.6, where Theta(sub e) is the zenith angle of the electron. The resonance matter effects are relevant for the interpretation of the Super-Kamiokande data. 30 refs, 9 figs.