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June 12 , 2007
DH 07 JH

Physics Professors’ Research Validated

DOE experiment confirms James Hill’s doctoral thesis refuting 1995 experiment on neutrino oscillation

Carson, CA A recent announcement by scientists at the Department of Energy’s (DOE) Fermilab significantly clarifies the overall picture of how neutrinos behave, backing up the research done by California State University, Dominguez Hills physics professors Kenneth Ganezer and James Hill.

The results of the so-named MiniBooNE (Booster Neutrino Experiment) resolve the questions raised by observations from an earlier DOE experiment—the Liquid Scintillator Neutrino Detector (LSND). This 1995 experiment was the first major project to claim strong evidence of neutrino oscillations, and yielded conclusions and results that Hill contradicted in his doctoral thesis, “An Analysis of Data from the LSND Experiment.” The date from the DOE experiment began to be compared with other data related to neutrino oscillations from the late 1990s to the present, and since its results, theorists have used “sterile” neutrinos to solve many problems in physics from supernova explosions to the mysterious dark matter that binds galaxies together.

“I did my thesis on LSND and came up with an analysis consistent with what MiniBooNE is now confirming,” says Hill. “Basically, I have been waiting the dozen years since my Ph.D. to have conclusive evidence outside of the LSND experiment that my analysis was the correct one.”

Neutrinos are particles that originate from nuclear beta decays and other weak-interaction decays, including those associated with the fusion reactions that power the sun and produce all of the elements heavier than helium in the core of the sun. Other sources of neutrinos include nuclear reactors, some beams from particle accelerators, and interactions of the solar wind with nuclei in the portion of the atmosphere 20 km above the Earth’s surface. Neutrinos are one of the most fundamental, numerous and least understood types of particles in the universe and differ from electrons in that they do not carry an electric charge and can pass through great distances in matter without being affected by it. The study of neutrinos helps scientists understand the sun, stars, and even the deep core of the Earth. It also provides the capability to detect extremely small trace amounts of radioactivity contained in samples of material, resulting in applications for homeland security, microelectronics, and space science.

“Since I have been at Dominguez Hills, neutrino oscillations, neutrino mass and the experimental information that these areas bring about physics beyond the standard model have become one of the most interesting topics in particle physics and physics in general,” Ganezer points out.

Currently, three types or "flavors" of neutrinos are known to exist: electron neutrinos, muon neutrinos and tau neutrinos. In the last 10 years, several experiments—including the LSND collaboration—have shown that neutrinos can oscillate from one flavor to another and back. However, reconciling the LSND observations with the oscillation results of other neutrino experiments would have required the presence of a fourth type of neutrino, with properties different from the three standard neutrinos, called a “sterile” neutrino because it does not participate in any of the standard interactions other than gravity. The existence of sterile neutrinos would throw serious doubt on the current structure of particle physics, known as the Standard Model of Particles and Forces, by involving a previously unknown interaction. Because of the far-reaching consequences of this interpretation, the LSND findings cried out for independent verification.

When Hill’s thesis was first published, it was a dissenting interpretation of the LSND data — data that had been put forward and sanctioned by only one of the LSND collaboration’s approximately 35 members. The particle physics community took the results of the full LSND collaboration as being the official interpretation of the LSND data and worthy of further study, even though many physicists in the field felt that the LSND collaboration had made the wrong conclusion by claiming that their data showed statistically significant evidence of neutrino oscillations, and viewed the LSND conclusion as being preliminary at best. At the time there were two other anomalous results involving neutrinos called the atmospheric neutrino anomaly and the solar neutrino problem, and the LSND data was looked at as yet another unexplained neutrino anomaly. Several years after the LSND claim was made, the atmospheric neutrino anomaly and the solar neutrino problem were explained as being due to neutrino oscillations. Since Jim Hill’s alterative analysis claimed only negative results with respect to neutrino oscillations it may have fallen from the forefront in a string of positive results on this topic.

“This makes a nice story to tell students about the way science works,” notes Hill. “A disputed result calls for a definitive experiment; someone does that experiment, and we all figure out what the truth was all along. It didn't go perfectly smoothly through the process in this case, but it got there.”

The MiniBooNE experiment, approved in 1998, took data for the current analysis from 2002 until the end of 2005 using neutrinos produced by the Booster accelerator at Fermilab. The experiment’s goal was to confirm or to refute the startling observations reported by the LSND collaboration, thus answering a long-standing question that has troubled the neutrino physics community for more than a decade.

The MiniBooNE collaboration used a completely blind-experimental technique to ensure the credibility of their analysis and results. While collecting their neutrino data, the MiniBooNE collaboration did not permit themselves access to data in the region, or "box," where they would expect to see the same signature of oscillations as LSND. When the MiniBooNE collaboration opened the box and "unblinded" its data less than three weeks ago, the telltale oscillation signature was absent.

“This dramatic and long-awaited result will help to clarify new and existing studies of neutrino oscillations and how this relatively new phenomenon provides clues to how the fundamental forces in nature are unified at high energy,” says Ganezer, who brought his research efforts in particle physics and neutrino physics to Dominguez Hills in 1990 as a full-time physics faculty member. “Now that the MiniBooNE has shown that LSND failed to see neutrino oscillations and the conclusion of Dr. Hill’s thesis to therefore be correct at the 98 percent confidence level, perhaps interest in his alternative analysis will be revitalized.”

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Last updated June 13, 2007, 11:22.m.
by Joanie Harmon-Whetmore