Upper limits for neutrino oscillationsν¯μ→ν¯efrom muon decay at rest

The KARMEN experiment at the spallation neutron source ISIS used ${\overline{\nu }}_{\mu }$ from ${\mu }^{+}$ decay at rest for the search of neutrino oscillations ${\overline{\nu }}_{\mu }\to {\overline{\nu }}_e$ in the appearance mode, with $p\left({\overline{\nu }}_e{,e}^{+}\right)n$ as a detection reaction of ${\overline{\nu }}_e.$ In total, 15 candidates satisfy all conditions for the ${\overline{\nu }}_e$ signature, in agreement with the background expectation of $15.8\pm 0.5$ events, yielding no indication for oscillations. A single event based likelihood analysis leads to upper limits on the oscillation parameters ${\sin }^2\left(2\mathrm{}\Theta \right)<\mathrm{}1.7\mathrm{}\times {10}^{-3}$ for $\Delta m^2>~100\hspace{0.5em}{\mathrm{eV}}^2$ and $\Delta m^2<0.055\mathrm{}\hspace{0.5em}{\mathrm{eV}}^2$ for ${\sin }^2\left(2\mathrm{}\Theta \right)=1\mathrm{}$ at 90% confidence. Thus, KARMEN does not confirm the LSND experiment and restricts significantly its favored parameter region for ${\overline{\nu }}_{\mu }\to {\overline{\nu }}_e.$