MINOS experiment sheds light on mystery of neutrino disappearance

April 6, 2006

AUSTIN, Texas—Physicists from The University of Texas at Austin, as part of an international collaboration of scientists, observed the disappearance of neutrinos during a Main Injector Neutrino Oscillation Search (MINOS) experiment, a finding that could help explain the role of these subatomic particles in the evolution of the universe.

Sending a high-intensity beam of muon neutrinos from Department of Energy’s Fermi National Accelerator Laboratory (Fermilab) site in Batavia, Ill., to a particle detector in Soudan, Minn., the scientists observed that a significant fraction of these neutrinos disappear. The observation is consistent with an effect known as neutrino oscillation, in which neutrinos change from one kind to another.

Karol Lang, professor of physics, Sacha Kopp, assistant professor of physics, and their students were involved in designing, building and testing the beam line and the detectors. They are analyzing data and made important contributions to the announced neutrino oscillation results.

The scientists announced their finding March 30 at Fermilab. These are the first results of the MINOS experiment.

“The MINOS experiment, and poignantly the first beam results, open a new era for experiments with neutrinos,” said Lang. “The well-controlled, high-power beam and two large magnetized detectors allow an unprecedented precision with which neutrinos can be studied. MINOS will be conducting measurements with neutrinos and anti-neutrinos for several years to come. The knowledge gained will shed more light on fundamental properties of these elusive particles which play a critical role in the evolution of stars and the universe.”

“Only a year ago we launched the MINOS experiment,” said Fermilab Director Pier Oddone. “It is great to see that the experiment is already producing important results, shedding new light on the mysteries of the neutrino.”

Nature provides for three types of neutrinos, yet scientists know very little about these “ghost particles,” which can traverse the entire Earth without interacting with matter. But the abundance of neutrinos in the universe, produced by stars and nuclear processes, may explain how galaxies formed and why antimatter has disappeared. Ultimately, these elusive particles may explain the origin of the neutrons, protons and electrons that make up all the matter in the world around us.

“Using a man-made beam of neutrinos, MINOS is a great tool to study the properties of neutrinos in a laboratory-controlled environment,” said Stanford University Professor Stan Wojcicki, spokesperson for the experiment.

Neutrinos are hard to detect, and most of the neutrinos traveling the 450 miles from Fermilab to Soudan—straight through the earth, no tunnel needed—leave no signal in the MINOS detector. If neutrinos had no mass, the particles would not change as they traverse the Earth and the MINOS detector in Soudan would have recorded 177 +/- 11 muon neutrinos. Instead, the MINOS collaboration found only 92 muon neutrino events—a clear observation of muon neutrino disappearance and hence neutrino mass.

Lang and his students led the effort to develop some of the central components of the MINOS detectors, while Kopp and his students worked on beamline production and the monitoring of particles existing in the beamline before the neutrinos reach the detectors.

University of Texas at Austin graduate students who worked on the project include Dharma Indurthy, Zarko Pavlovic, Tom Osiecki and Rustem Ospanov. Former students involved with the project include Mike Kordosky and Patricia Vahle, postdoctoral fellows at University College London, and Bob Zwaska, a Peoples Fellow at Fermilab. 

“We’ve been very fortunate to work with some excellent students,” Kopp said.  “They are really leaders within the MINOS collaboration.”

The MINOS experiment includes about 150 scientists, engineers, technical specialists and students from 32 institutions in 6 countries, including Brazil, France, Greece, Russia, the United Kingdom and the United States. The institutions include universities as well as national laboratories. The U.S. Department of Energy provides the major share of the funding, with additional funding from the U.S. National Science Foundation and from the United Kingdom’s Particle Physics and Astronomy Research Council.

For more information contact: Karol Lang, 512-471-3528; Lee Clippard, College of Natural Sciences, 512-232-0675.