We observe a net beam-excess of $8.7 \pm 6.3$ (stat) $\pm 2.4$ (syst) events, above 160 MeV, resulting from the charged-current reaction of $\nu_{ \mu}$ and/or $\bar\nu_{ \mu}$ on C and H in the LSND detector. No beam related muon background is expected in this energy regime. Within an analysis framework of $\pi^0 \to \nu_{ \mu}\bar\nu_{ \mu}$, we set a direct upper limit for this branching ratio of $\Gamma(\pi^0 \to \nu_\mu \bar\nu_\mu) / \Gamma(\pi^0 \to all) < 1.6 \times 10^{ -6}$ at 90% confidence level.
Categories: hep-ex