LSND strengthens evidence for neutrino oscillations

Contact: Todd Hanson, tahanson@lanl.gov, (505) 665-2085 (01-122)

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LOS ALAMOS, N.M., Dec. 4, 2001 -- A collaboration of university scientists and researchers working at Los Alamos National Laboratory has published the final paper from the Liquid Scintillator Neutrino Detector (LSND) experiment. The results, based on six years of data collection, strengthen previously published, but controversial LSND results and provide further evidence of neutrino oscillation and mass.

The LSND data, collected from 1993 to 1998, suggest that muon anti-neutrinos oscillate into electron anti-neutrinos. Combined with other data on neutrino oscillations, the results indicate that neutrinos represent roughly one percent or more of the universe's total mass.

The LSND results, which will be published in Physical Review D on Dec. 1, are based on data collected at the Los Alamos Neutron Science Center accelerator. During the collection period from 1993-1998, LANSCE delivered 180 trillion-billion (180,000,000,000,000,000,000,000) protons to the LSND target, a tank filled with 167 tons of mineral oil (baby oil) and 14 pounds of organic scintillator. This oil/scintillator mixture allowed the detection of both Cerenkov light and scintillation light via 1220 light sensitive tubes and provided excellent particle identification.

Neutrino oscillations have been employed to explain the apparent deficit of solar electron-neutrinos and atmospheric muon-neutrinos. The solar and atmospheric experiments have been confirmed by other experiments, while the LSND remains uncomfirmed. An independent experiment is needed to prove whether the events observed by LSND are indeed due to neutrino oscillations. The MiniBooNE experiment, currently under construction at Fermilab, is designed to provide a definitive test of the LSND neutrino oscillation results, and if the results are verified, to make a precision measurements of the oscillation parameters.

Scientists find it difficult to explain the solar, atmospheric, and LSND results using only the three known neutrino types: the electron, muon, and tau neutrinos. This difficulty causes the LSND results to be controversial. It has been hypothesized that some unknown new phenomenon--such as a fourth 'sterile' neutrino with a much weaker interaction with matter than normal neutrinos or large extra dimensions with different neutrino masses--might explain the data. Such new phenomena would have an enormous impact on the standard model of particle physics and would have very broad implications for future research in the fields of nuclear physics, high-energy physics, and astrophysics.

The LSND collaboration consists of physicists from the University of Alabama, University of California at Riverside, University of California at San Diego, University of California at Santa Barbara, Embry Riddle Aeronautical University, Indiana University, Los Alamos National Laboratory, Louisiana State University, Southern University, and Temple University.

Los Alamos National Laboratory is operated by the University of California for the U.S. Department of Energy's National Nuclear Security Administration.

Additional news releases from the Los Alamos Neutron Science Center (LANSCE)