Evidence of a new subnuclear particle -- an exotic meson -- has been discovered by a team of physicists from the University of Notre Dame and six other institutions. Long theorized, the particle had been undetected until now, said Neal Cason, professor of physics at Notre Dame and a cospokesman on the project.
The elementary particle physics group at Notre Dame -- professors Cason, William Shephard, John LoSecco and James Bishop -- and 47 others are investigators in this research, which has been published in the Sept. 1 issue of Physical Review Letters.
"Our observation of the exotic meson is significant to understanding the basic forces at work between the elementary particles," Cason said. "Comparing our results with current theoretical models will allow us to begin the detailed understanding of these forces."
The experiment, titled E852 and conducted at Brookhaven National Laboratory on Long Island, is reported in the dissertation of Notre Dame doctoral student David Thompson. Five other Notre Dame graduate students are among the 51 investigators in the research.
"This is a very important discovery," said Ted Barnes, a theoretical physicist at Oak Ridge National Laboratory and professor of physics at the University of Tennessee. "Theorists have predicted the existence of the exotic meson since the late 1970s, but E852 may have found the smoking gun for their existence. It's a benchmark that will set the mathematical scales for future experimentation and theoretical study."
A meson is a very unstable, medium-mass elementary particle with a short life span that is similar to but smaller than a proton or neutron. All three are composed of the most basic elementary particle, the quark. Protons and neutrons are made up of three quarks, while ordinary mesons are composed of one quark and one antiquark.
"Over the years, we've observed and catalogued mesons, with much of the work being done here at Notre Dame," said Cason. "What we've been searching for is a new form of a meson -- the exotic meson."
The building blocks of one type of exotic meson are a quark, an antiquark and gluon, yet another elementary particle that "glues" together the quark and antiquark.
Using high-energy particle beams at the Brookhaven accelerator, Cason said, "We discovered a meson that we know is not made up of a quark and antiquark, which means it must be an exotic meson. There are a number of different kinds of exotic mesons and we're now going to begin work to determine which kind this is."
Mesons and exotic mesons "are not a part of our everyday life," Cason said. "Because they are unstable, you cannot make higher forms of matter with them."
However, the discovery of the exotic meson is significant because it will allow physicists to expand their understanding of nature at its most fundamental level, Cason said.
"When we search for matter like this (the exotic meson), what we're really doing is looking for the fundamental forces between matter," Cason said. "As far as we know, there are only four fundamental forces in nature -- the gravitational, the electrical, the strong and the weak forces. This research will help us better understand the properties of the strong force."
The research began in 1989 and was funded by the High Energy Physics and Nuclear Physics Divisions of the National Science Foundation and the Department of Energy through Brookhaven.
Other institutions participating in the collaborative project are Brookhaven, the University of Massachusetts at Dartmouth, Northwestern University, Rensselaer Polytechnic Institute, and Moscow State University and the Institute for High Energy Physics in Russia.
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