Search for flavor-changing nonstandard neutrino interactions using ${\nu }_e$ appearance in MINOS

We report new constraints on flavor-changing nonstandard neutrino interactions from the MINOS long-baseline experiment using ${\nu }_e$ and ${\overline{\nu }}_e$ appearance candidate events from predominantly ${\nu }_{\mu }$ and ${\overline{\nu }}_{\mu }$ beams. We used a statistical selection algorithm to separate ${\nu }_e$ candidates from background events, enabling an analysis of the combined MINOS neutrino and antineutrino data. We observe no deviations from standard neutrino mixing, and thus place constraints on the nonstandard interaction matter effect, $|{ϵ}_{e\tau }|$, and phase, $({\delta }_{CP}+{\delta }_{e\tau })$, using a 30-bin likelihood fit.

Figure 1

Far Detector Monte Carlo ${\nu }_e+{\overline{\nu }}_e$ CC reconstructed energy distributions shown for standard oscillation and for two illustrative nonstandard oscillation cases. Normal mass hierarchy, $|\mathrm{\Delta }{m}_{31}^2|=2.41\times {10}^{-3}{\mathrm{eV}}^2$, ${\delta }_{CP}=0$, ${\theta }_{23}=\pi /4$ and ${\sin }^2(2{\theta }_{13})=0.084$ are assumed. Unspecified NSI parameters are set to zero.

Figure 2

The reconstructed energy distributions for three ranges of ${\alpha }_{\mathrm{LEM}}$. The 5–8 GeV region is combined into a single bin for the fit. The best fit that includes systematics is shown assuming normal mass hierarchy, with $|{ϵ}_{e\tau }|=0.74$ and $({\delta }_{CP}+{\delta }_{e\tau })=1.35\pi$. It is overlaid atop the standard oscillation predictions from [22].

Figure 3

90% C.L. in the $|{ϵ}_{e\tau }|,({\delta }_{CP}+{\delta }_{e\tau })$ parameter space for normal (top) and inverted (bottom) neutrino mass hierarchy using ${\nu }_e$ and ${\overline{\nu }}_e$ appearance candidates in the MINOS Far Detector. The shaded areas to the left of the solid contours indicate the MINOS allowed regions where additional oscillation parameters, including NSI, were included in the fit. The dotted contours show the limits where the additional oscillation parameters were fixed to the mean values shown in Table 1.