Search for neutrino oscillations in the BNL E8-16 experiment

Experiment PS 191 at CERN was looking for decays of hypothetical heavy neutrinos in a low energy upsilon/sub μ/ beam. It found an apparent excess of neutrino interactions showing an electron, about 3 times the number expected from the fluxes of upsilon/sub e/ calculated with standard programs. The result was limited by statistics and not optimized for this search. If the events seen were indeed upsilon/sub e/ interactions and if the flux calculations were reliable, then the signal could be an indication of the oscillation upsilon/sub μ/ → upsilon/sub e/. To investigate further this result the detector was moved to BNL where the neutrino beam is about 5 times more intense. The experiment was rerun in better conditions with an unbiased trigger and more matter for shower containment. A total of 10/sup 19/ protons on target were accumulated both for neutrinos and antineutrinos. This represents more than an order of magnitude gain with respect to the CERN experiment. The detector, although light (upsilon 7 tons of fiducial mass) has the advantage of being very fine grain. It is constructed of 3 mm thick iron plates and flash tube chambers. The tubes have transverse dimensions 5 x 5 mm/sup 2/ and cover 3 x 6 m/sup 2/ for a total of 35,000 channels. The granularity for electromagnetic showers is 17% of a radiation length. The search for oscillation is a relative measurement of the number of events showing 2 branches, either with or without and electromagnetic shower. This is a direct estimate of the ratio upsilon/sub e//upsilonμ