Number 239 (Story #1), September 8, 1995 by Phillip F. Schewe and Ben Stein DO NEUTRINOS OSCILLATE? That is, do they mutate from one type into another, violating a hitherto empirical law called conservation of lepton number? Do neutrinos have a nonzero mass, an issue that has a bearing on the solar neutrino problem and on the search for dark matter? Earlier this year, unofficial reports (Update 213) from a Los Alamos experiment suggested that neutrinos do oscillate. The findings of the Liquid Scintillator Neutrino Detector (LSND) collaboration are now to be published in Physical Review Letters (October 2, C. Athanassopoulos et al.). In this experiment muon antineutrinos would presumably transform in flight into electron antineutrinos which then enter a detector filled with 180 tons of mineral oil. There they would occasionally strike a proton, creating a positron and a neutron. Like the search for top quarks at Fermilab, the search for electron antineutrino interactions at Los Alamos is a numbers game. After months of recording data, the LSND team reports a harvest of 9 events with an expected background of 2 events. In an unusual move, Physical Review Letters is publishing in the same issue another article by a lone member of the group. James Hill, a recent PhD at the University of Pennsylvania, believes that events from more of the active detector volume should be excluded from the final analysis, the better to reject spurious background contamination by, for example, cosmic ray neutrinos entering the detector from the bottom. Hill's alternative analysis renders 5 events against a background of 6 events, which is the same thing as saying that no discernible neutrino oscillation "signal" is present in the data. (Science journalists can obtain copies of the two papers from AIP Public Information, physnews@aip.org)