A High Statistics Search for muon-neutrino(anti-muon-neutrino) ---> electron-neutrino(anti-electron-neutrino) Oscillations in the Small Mixing Angle Regime

TL;DR

This paper reports a high-statistics search for muon-neutrino to electron-neutrino oscillations at high energies, setting new stringent limits on oscillation parameters and testing neutrino universality, thereby challenging previous experimental claims.

Contribution

It provides the most stringent limits to date on neutrino oscillations in the high $\Delta m^2$ region and introduces a novel statistical method for identifying $ u_e$ interactions.

Findings

Set a 90% confidence upper limit of $1.1 imes 10^{-3}$ on $sin^2 2 heta$ at $\Delta m^2 \\sim 300 eV^2$

Excluded high $\Delta m^2$ oscillation regions favored by LSND

Measured the $ u_\mu$-to-$ u_e$ cross-section ratio as $1.026 \\pm 0.055$

Abstract

Limits on $\nu_\mu (\overline{\nu}_\mu) \to \nu_e (\overline{\nu}_e)$ oscillations based on a statistical separation of $\nu_e N$ charged current interactions in the CCFR detector at Fermilab are presented. $\nu_e$ interactions are identified by the difference in the longitudinal shower energy deposition pattern of $\nu_e N \rightarrow eX$ versus $\nu_\mu N \to \nu_\mu X$ interactions. Neutrino energies range from 30 to 600 GeV with a mean of 140 GeV, and $\nu_\mu$ flight lengths vary from 0.9 km to 1.4 km. The lowest 90% confidence upper limit in $sin^2 2\alpha$ of $1.1 \times 10^{-3}$ is obtained at $\Delta m^2 \sim 300 eV^2$. For $sin^2 2\alpha = 1$, $\Delta m^2 > 1.6 eV^2$ is excluded, and for $\Delta m^2 \gg 1000 eV^2$, $sin^2 2\alpha > 1.8 \times 10^{-3}$ is excluded. This result is the most stringent limit to date for $\Delta m^2 > 25 eV^2$ and it excludes the high $\Delta m^2$ oscillation region favoured by the LSND experiment. The $\nu_\mu$-to-$\nu_e$ cross-section ratio was measured as a test of $\nu_\mu (\bar\nu_\mu) \leftrightarrow \nu_e (\bar\nu_e)$ universality to be $1.026 \pm 0.055$.