Improved search for muon-neutrino to electron-neutrino oscillations in MINOS

TL;DR

The results of a search for ν(e) appearance in a ν (μ) beam in the MINOS long-baseline neutrino experiment find that 2 sin(2) (θ(23))sin(2)(2θ (13))<0.12 at 90% confidence level for δ = 0 and the normal (inverted) neutrinos mass hierarchy.

Abstract

We report the results of a search for $ν_{e}$ appearance in a $ν_μ$ beam in the MINOS long-baseline neutrino experiment. With an improved analysis and an increased exposure of $8.2\times10^{20}$ protons on the NuMI target at Fermilab, we find that $2\sin^2(θ_{23})\sin^2(2θ_{13})<0.12\ (0.20)$ at 90% confidence level for $δ\mathord{=}0$ and the normal (inverted) neutrino mass hierarchy, with a best fit of $2\sin^2(θ_{23})\sin^2(2θ_{13})\,\mathord{=}\,0.041^{+0.047}_{-0.031}\ (0.079^{+0.071}_{-0.053})$. The $θ_{13}\mathord{=}0$ hypothesis is disfavored by the MINOS data at the 89% confidence level.

Figures (3)

• Figure 1: [Top] Distribution of the LEM discriminant for events in the Near Detector that pass the pre-selection requirements. Data (points) and Monte Carlo simulation (histogram) are shown, with the magnitude of the systematic uncertainty indicated by the band. This uncertainty is highly correlated between the ND and FD and thus cancels out to a large degree when we form our FD predictions. [Bottom] Expected background and signal distributions in the Far Detector for $\sin^2(2\theta_{13})\mathord{=}0.1$. The signal distribution has been multiplied by 10 for visibility.
• Figure 2: Reconstructed energy spectra for $\nu_{e}$ CC candidate events in the Far Detector. The black points indicate the data with statistical error bars shown. The histogram indicates the expected background (unfilled area) together with the contribution of $\nu_{\mu}\, \rightarrow\, \nu_{e}$ signal (hatched area) for the best-fit value of $\sin^2(2\theta_{13})\,\mathord{=}\,0.041$.
• Figure 3: Allowed ranges and best fits for $2\sin^2(\theta_{23})\sin^2(2\theta_{13})$ as a function of $\delta$. The upper (lower) panel assumes the normal (inverted) neutrino mass hierarchy. The vertical dashed line indicates the CHOOZ 90% C.L. upper limit assuming $\theta_{23}\,\mathord{=}\frac{\pi}{4}$ and $\Delta m^2_{32}\,\mathord{=}\,2.32\mathord{\times}10^{-3}\ \mathrm{eV}^2$ref:chooz.