Long the fixation of physicists worldwide, a tiny particle is found
BUFFALO, N.Y. -- After decades of intensive effort by both experimental and theoretical physicists worldwide, a tiny particle with no charge, a very low mass and a lifetime much shorter than a nanosecond, dubbed the "axion," has now been detected by the University at Buffalo physicist who first suggested its existence in a little-read paper as early as 1974.
The finding caps nearly three decades of research both by Piyare Jain, Ph.D., UB professor emeritus in the Department of Physics and lead investigator on the research, who works independently -- an anomaly in the field -- and by large groups of well-funded physicists who have, for three decades, unsuccessfully sought the recreation and detection of axions in the laboratory, using high-energy particle accelerators.
The paper, available online in the British Journal of Physics G: Nuclear and Particle Physics at http://www.iop.org/EJ/abstract/0954-3899/34/1/009, will be published in the January 2007 issue.
Results first were presented during a two-day symposium held in October at UB that celebrated Jainís 50-year career in the physics department in the College of Arts and Sciences.
During that symposium, the world-renowned and Nobel Prize-winning scientists in attendance expressed astonishment and delight that the axion finally might have been found.
The axion has been seen as critical to the Standard Model of Physics and is believed to be a component of much of the dark matter in the universe.
"These results show that we have detected axions, part of a family of particles that likely also includes the very heavy Higgs-Boson particle, which at present is being sought after at different laboratories," said Jain.
The story of the search for the axion particle in high-energy physics -- not to be confused with the search by cosmologists and astrophysicists for axions produced by the sun -- reads almost like a novel,
with veritable armies of physicists committing many years of research and passion to its discovery starting in the 1970s.
In 1977, theoretical physicists predicted that there should exist a particle with characteristics very similar to those described in Jainís papers; in that publication, the term "axion" was coined. After that theoretical work, there was a mushrooming of papers from both theoretical and experimental physicists all chasing the axion using low-, medium- and high-energy accelerator beams from different laboratories worldwide.
But when it proved to be too elusive, many in the physics community then abandoned the search in the 1990s, based on puzzling evidence that perhaps this tantalizing particle didnít exist after all. Some groups flatly denied its existence and began referring to it as a "phantom."
Jainís initial interest in the elusive particles originated with work he began publishing in 1974 in Physical Review Letters and other journals that demonstrated evidence for particles with very low mass and very short lifetimes during particle accelerator experiments he conducted at Fermilab and Brookhaven National Laboratory.
At the time, Jainís papers elicited little interest from other physicists.
"This particle was there in my original paper in 1974," he said. "The experiment gave a hint that these particles existed but did not generate sufficient statistics to prove it. I knew I had to wait until a heavy ion beam at very high energy was available at a new accelerator."
As recently as 1999, a project called the CERES experiment at CERN in Geneva again focused on attempting to detect the axion, but that project also was unsuccessful.
The problem, according to Jain, was with their detector, which was electronic, the standard used in high-energy physics experiments today.
"They didnít know how to handle the detector for short-lived particles," Jain said. "I knew that for this very short-lived particle -- 10-13 seconds -- the detector must be placed very near the interaction point where the collision between the projectile beam and the target takes place so that the produced particle doesnít run away too far; if it does, it will decay quickly and it will be completely missed. That is what happened in most of the unsuccessful experiments." Instead, Jain used a visual detector, made of three-dimensional photographic emulsions, which act as both target and detector and that therefore can detect very short-lived particles, such as the axion. However, use of such a detector is so specialized that to be successful, it requires intensive training and experience. In the 1950s, Jain was trained to use this type of detector by its developer, the Nobel laureate, British physicist Cecil F. Powell. Jain has used it throughout his career to successfully detect other exotic
phenomena, such as the charm particle, the anomalon, the quark-gluon plasma and the nuclear collective flow. In Jainís successful experiment, the axions were produced under extreme conditions of high temperature and high pressure, using a heavy ion lead beam with a total energy of 25 trillion electron volts at CERN in Geneva.
His experiments generated 1,220 electron pairs with identified vertices, the origin of each pair. They peaked at a distance of just 200-300 microns from the interaction point where the collisions take place in the emulsion.
"Only at that very short distance did I find the peak signal of this very-low-mass, short-lived particle with a neutral charge," he said.
After they are produced, axions rapidly decay into two electron pairs, the electron and the positron, he explained.
"We identified each vertex for each electron pair and we would not accept any electron pair unless we knew its vertex," he said. "There was a congestion of all kinds of low mass particles, including axions, near the detector. The background has to be filtered out from this congestion in order to obtain the signal of the axion."
Jainís co-author on the paper is Gurmukh Singh, then a post-doctoral researcher at UB and now a visiting assistant professor in the Department of Computer and Information Sciences at the State University of New York at Fredonia.
During Jainís long and illustrious career at UB, he published 175 scientific papers on a wide variety of physics topics, ranging from cosmic ray research performed on balloon flights to National Institutes of Health-funded studies on bone tissue to find more effective cancer therapies. "After half a century as a scientist at UB, I find that with the discovery of this axion, my mission is complete," he concluded.
The University at Buffalo is a premier research-intensive public university, the largest and most comprehensive campus in the State University of New York.
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