MiniBooNE Project Results Validates Research of CSUDH Physics Professors

An announcement in April by scientists at the Department of Energy’s (DOE) Fermilab, significantly clarifies the overall picture of how neutrinos behave, backing up 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 data from this DOE experiment began to be compared with other data related to neutrino oscillations from the late 1990s to the present, and since its results were released, 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.” (To read Hill's archived thesis, click here.)

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 primary cosmic rays with nuclei in the portion of the atmosphere 20 kilometers 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 travel large distances inside space that is filled with matter without being affected by it. The study of neutrinos helps scientists understand the sun, stars and the 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 concerning 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, muon, and tau neutrinos. In the past 10 years, several experiments—including LSND —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 theory that is used to describe nearly all 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 collaboration as being the official interpretation of the 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 at best preliminary. 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 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 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 how 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 blind-experimental technique to ensure the credibility of their analysis and results. While collecting their neutrino data, MiniBooNE members did not allow themselves access to data in the region of their parameter space or "box," where they would expect to see the same signature of oscillations as that observed by LSND. When MiniBooNE “opened the box” and "unblinded" its data this spring, 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 relates to the expected unification of the fundamental forces at high energies,” says Ganezer, who brought his research efforts in particle and neutrino physics to Dominguez Hills in fall 1990 as a full-time faculty member. “Now that MiniBooNE has shown that LSND failed to see neutrino oscillations and that the conclusion of Dr. Hill’s thesis is correct, at the 98 percent confidence level, perhaps interest in his alternative analysis will be revitalized.”

- Joanie Harmon-Whetmore