A Search for Neutrino Oscillations.

Abstract

A search for neutrino oscillation has been carried out at LAMPF (the Los Alamos Meson Physics Facility). The engineering run in the 1986 cycle has demonstrated that the detector works as designed. The probability of oscillation between two neurino types $\nu\sb1$ and $\nu\sb2$ can be parameterized by two variables: (1) the difference between the squares of the masses of two mass eigenstates $\delta$m$\sp2$ $(\equiv\ \vert$m$\sb1\sp2$ - m$\sb2\sp2\vert),$ and (2) the mixing angle $(\theta)$ between the two states. In this experiment, we set limits on the oscillations $\bar\nu\sb\mu$ $\to$ $\bar\nu\sb{\rm e}$ and $\nu\sb{\rm e}$ $\to$ $\bar\nu\sb{\rm e}$ as a function of $\delta$m$\sp2$ and sin$\sp2 2\Theta$. For the $\bar\nu\sb\mu \to \bar\nu\sb{\rm e}$ oscillation, we obtained sin$\sp22\theta$ $<$ 0.14 (90% C.L.) in the limit of large mass difference $\delta$m$\sp2$ between neutrino mass eigenstates m$\sb1$ and m$\sb2$; and an upper limit on the product $\delta$m$\sp2$sin$\sp2 2\theta$ $<$ 0.35 eV$\sp2$ in the limit of small mass difference. For the $\nu\sb{\rm e}\to\bar\nu\sb{\rm e}$ oscillation, we obtained sin$\sp2 2\theta$ $<$ 0.21 (90% C.L.) in the limit of large mass difference $\delta$m$\sp2$ and an upper limit on the product $\delta$m$\sp2$sin$\sp2 2\theta$ $<$ 0.39 eV$\sp2$ in the limit of small mass difference.