Search for Neutrino Oscillations at LAMPF.

The E645 experiment at Los Alamos is designed to search for the phenomenon of neutrino oscillations. The particular modes of oscillation searched for are: |nu_mu to |nu _{rm e} and nu _{rm e} to |nu _{rm e}.. The neutrino source is the LAMPF proton beam stop. The detector consists of 20 tons of liquid scintillator for particle calorimetry and proportional drift tubes for particle tracking. The |nu_{ rm e} detection mechanism employs the positron trigger that occurs from the | nu_{rm e} inverse beta decay reaction on the free protons contained in the liquid scintillator ({rm CH}_2) : |nu_{rm e} + {rm p} to {rm e}^+ + {rm n}^0.. A preliminary data run was performed in the fall of 1986. The analysis showed that there were 0.04 ( +/-0.6) beam induced events per LAMPF-day; a result that is consistent with zero oscillation events for the data run. The null result confirms an excluded range of {rm sin}^2 2theta and | o{rm m}^2 values for a |nu_ mu to |nu_{rm e} oscillation. The E645 experiment can also uniquely rule out the exclusive nu_{rm e } to |nu_{rm e} oscillation process, which is expected if the nu_{rm e} is a Majorana neutrino. The 11.4 LAMPF-day run yields the only available limits on this oscillation process.