High Statistics Search for ${\nu }_{\mu }\left({\overline{\mathit{\nu }}}_{\mathit{\mu }}\right)\to {\nu }_e\left({\overline{\nu }}_e\right)$ Oscillations in the Small Mixing Angle Regime

Limits on ${\nu }_{\mu }\left({\overline{\nu }}_{\mu }\right)\to {\nu }_e\left({\overline{\nu }}_e\right)$ oscillations based on a statistical separation of ${\nu }_{e}N$ charged current interactions in the CCFR detector at Fermilab are presented. Neutrino energies range from 30 to 600 GeV with a mean of 140 GeV, and ${\nu }_{\mu }$ flight lengths vary from 0.9 to 1.4 km. The result excludes oscillations in the region with ${sin}^{2}2\alpha >1.8\mathrm{}\times {10}^{-3\mathrm{}}$ for large $\Delta m^2(>1000\mathrm{}{\mathrm{eV}}^2)$ and $\Delta m^2>1.6\mathrm{}{\mathrm{eV}}^2$ for ${sin}^{2}2\alpha =1\mathrm{}$. This result is the most stringent limit to date for $\Delta m^2>25\mathrm{}{\mathrm{eV}}^2$ and it excludes the high $\Delta m^2$ oscillation region favored by the LSND experiment. The ${\nu }_{\mu }$-to- ${\nu }_e$ cross-section ratio was measured as a test of ${\nu }_{\mu }\left({\overline{\nu }}_{\mu }\right)\leftrightarrow {\nu }_e\left({\overline{\nu }}_e\right)$ universality to be $1.026\pm 0.025\left(\mathrm{stat}\right)\pm 0.049\left(\mathrm{syst}\right)$.