Search for matter-dependent atmospheric neutrino oscillations in Super-Kamiokande

We consider ${\nu }_{\mu }\to {\nu }_{\tau }$ oscillations in the context of the mass varying neutrino (MaVaN) model, where the neutrino mass can vary depending on the electron density along the flight path of the neutrino. Our analysis assumes a mechanism with dependence only upon the electron density, hence ordinary matter density, of the medium through which the neutrino travels. Fully-contained, partially-contained and upward-going muon atmospheric neutrino data from the Super-Kamiokande detector, taken from the entire SK-I period of 1489 live days, are compared to MaVaN model predictions. We find that, for the case of 2-flavor oscillations, and for the specific models tested, oscillation independent of electron density is favored over density dependence. Assuming maximal mixing, the best-fit case and the density-independent case do not differ significantly.

Figure 1

$\Delta m^2\to \Delta m^2\times (\frac{{\rho }_e}{{\rho }_o}{)}^n$ (including air path length). Upper plot shows relative-${\chi }^2$ confidence level contours on the $\Delta m^2$ versus $n$ plane, obtained when taking into account both high and low density matter path lengths. The lower plots display the ${\chi }^2-{\chi }_{\min }^2$ contours, with confidence levels shown, at the best-fit parameter values.