Atmospheric neutrino data : Active-Active × Active-Sterile oscillations

Atmospheric showers are initiated when primary cosmic rays hit the Earth’s atmosphere. Secondary mesons produced in this collision, mostly pions and kaons, decay and give rise to electron and muon neutrino and anti-neutrinos fluxes [1]. In the past Fréjus and NUSEX [2] reported a R-value (R = (μ/e)data/(μ/e)MC) consistent with one, therefore other detectors like Kamiokande, IMB and Soudan-2 [3] have measured R significantly smaller than unity. Recent Super-Kamiokande high statistics observations [4] indicate that the deficit in the ratio R is due to the number of neutrinos arriving to the detector at large zenith angles. The main aim of this talk is to compare the active-active and active-sterile neutrinos oscillation channels to the atmospheric neutrino anomaly using the the new sample of 33.0 kt-yr of Super-Kamiokande data. This analysis uses the latest improved calculations of the atmospheric neutrino fluxes as a function of zenith angle, taking into account a variable neutrino production point [5]. The expected neutrino event number both in the absence and the presence of oscillations can be written as: