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Last modified: Friday, April 13, 2007

Results from Fermilab experiment resolve long-standing neutrino question

FOR IMMEDIATE RELEASE
April 13, 2007

NOTE TO EDITORS: Photos and graphics of the MiniBooNE experiment are available at http://www.fnal.gov/pub/presspass/images/BooNE-images.html

BLOOMINGTON, Ind. - A team of 77 scientists from 17 universities and laboratories, including five physicists from Indiana University Bloomington, announced Wednesday (April 11) their first findings from an experiment at Fermi National Accelerator Laboratory designed to test the current structure of particle physics, known as the Standard Model of Particles and Forces.

The standard model appears safe for the time being, at least.

These results resolve questions that were raised by an experiment at Los Alamos National Laboratory in the 1990s, called the Liquid Scintillator Neutrino Detector, which appeared to contradict findings of other neutrino experiments worldwide. The Fermilab experiment's goal was to either confirm or refute the LSND observations, which have troubled the neutrino physics community for more than a decade.

"It was very important to verify or refute the surprising LSND result," said Robin Staffin, associate director for high energy physics at the U.S. Department of Energy.

Currently, three types of neutrinos are known to exist. Several experiments, including LSND, have shown that neutrinos can oscillate from one type to another and back. However, the LSND observations implied the presence of a fourth type of neutrino, with properties different from the three standard neutrinos. Finding evidence that the new type of neutrino really exists would have thrown serious doubt on the standard model. Instead, the Fermilab experiment decisively ruled out the interpretation of the LSND results as being due to oscillation between two types of neutrinos.

IU physics professor Rex Tayloe, part of the IU team at Fermilab, said, "No obvious problem was found with LSND. Our experiment just did not reproduce the LSND experiment in a way that was expected." Tayloe also participated in the LSND experiment before joining the IU faculty.

Other members of the IU group at Fermilab were physics professor Hans-Otto Meyer, postdoctoral fellow Chris Polly, and graduate students Chris Cox and Teppei Katori.

The Fermilab experiment is called MiniBooNE (for Booster Neutrino Experiment). For its observations, MiniBooNE relied on a 250,000-gallon tank filled with mineral oil. An array of light-sensitive photomultiplier tubes, mounted inside the tank, detected the light from collisions between neutrinos made by the accelerator and carbon nuclei of the oil molecules.

"Our group has worked on the MiniBooNE experiment since it was proposed in 1998," Tayloe said. "We contributed to the detector by testing the mineral oil in the IU Cyclotron Facility's proton beam. This allowed for a more controlled and accurate measurement of the light emitted than is possible within the experiment at Fermilab. We also wrote the software that collects the data. Recently we have worked on the analysis of the data for this result."

The purpose of the MiniBooNE project is to better understand the standard model of particle physics, Tayloe said.

"It has been established that neutrinos have mass, but they are much lighter than any other particle, such as the quarks inside a proton or electron. If we can understand the mass of neutrinos by studying neutrino oscillations, we can perhaps understand some of the mystery of mass in general," he said.

Though the first results were decisive, the MiniBooNE collaboration has more work ahead.

"As in many particle physics experiments, we have a result that answers some questions and raises others," said MiniBooNE co-spokesperson William Louis of Los Alamos National Laboratory, who also worked on the original LSND experiment.

MiniBooNE physicists are supported by funding from the Department of Energy and the National Science Foundation.

The MiniBooNE institutions:

1. University of Alabama
2. Bucknell University
3. University of Cincinnati
4. University of Colorado
5. Columbia University
6. Embry Riddle Aeronautical University
7. Fermi National Accelerator Laboratory
8. Imperial College-London (UK)
9. Indiana University
10. Los Alamos National Laboratory
11. Louisiana State University
12. University of Michigan
13. Princeton University
14. Saint Mary's University of Minnesota
15. Virginia Polytechnic Institute and State University
16. Western Illinois University
17. Yale University