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: anti nu/sub μ/ → anti nu/sub e/ and nu/sub e/ → anti nu/sub 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 anti nu/sub e/ detection mechanism employs the positron trigger that occurs from the anti nu/sub e/ inverse beta decay reaction on the free protons contained in the liquid scintillator (CH2): anti nu/sub e/ + p → e+ + n0. 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 sin22theta and anti om2 values for a anti nu/sub μ/ → anti nu/sub e/ oscillation. The E645 experiment can also uniquely rule out the exclusive nu/sub e/ → anti nu/sub e/ oscillation process, which is expected if the nu/sub e/ is a Majorana neutrino. The 11.4 LAMPF-day run yields the only available limits on this oscillation process