Nov. 13, 2006
UI Particle Physics Research Team Observes New Particle
In the continuing search for characteristics that distinguish matter from anti-matter, a University of Iowa particle physics research group has discovered a new particle whose existence was already anticipated.
The finding was announced at the International Conference in High Energy Physics (ICHEP 2006) held July 26 through Aug. 2 in Moscow, Russia, and in the online publication "hep-ex/0608055" and has been accepted for publication in Physical Review Letters, the journal of the American Physical Society.
The research group -- headed by Usha Mallik, professor in the UI College of Liberal Arts and Sciences Department of Physics and Astronomy -- reports observing a new particle that is an excited state of a particle called the omega-c and having a mass widely predicted by many theorists. The group made their observations while working on the Stanford Linear Accelerator Center (SLAC) BABAR experiment, a major high-energy physics activity.
The new particle decays into the omega-c via the emission of a photon. Working in collaboration with researchers from the State University of New York-Albany, Mallik and her group reported the first observation of this excited omega-c state, the only such state not previously observed in this category.
Said Mallik: "These kinds of particles, consisting of the heavy quarks, were formed in the early universe when the energy density was very high. In order to understand the nature of the basic forces at play in the very early universe after the "Big Bang", particle physicists try to recreate such environments for a very short time in the accelerators where, in this case, electrons and their anti-particles (positrons) are accelerated at very high energies and then collided, producing very high energy density under carefully controlled environments. The observations of these predicted states at the expected energies mean we are on the right track in our quest."
The search for the basic building blocks of all matter can be traced from the ancient Greeks right up to the present day. Today, scientists know that particles called "quarks" are the most basic building blocks of protons and neutrons, which, in turn, are the constituents of atomic nuclei. Particle physicists have verified that there are six types of quarks, top or truth (t), bottom or beauty (b), charm (c), strange (s), up (u) and down (d). The up and down quarks are the lightest and most stable ones found in the nucleus. The strange, charm, bottom and top get progressively heavier, and are not observed in nature.
Both the omega-c particle and its excited state are comprised of one charm and two strange quarks.
In the BABAR experiment, also known as a B-factory, a B particle and an anti-B particle pair are produced in a high-rate, high-energy electron positron collider. The B contains an anti-b and a down or an up quark; in the case of the anti-B counterpart, it's a b and an anti-down or an anti-up quark. These decay immediately into many other particles, the footprints of which are left in the various pieces of the detector. By studying these footprints, scientists reconstruct the previous steps of their origin, one step at a time. The footprints also allow physicists to carefully study differences in the behavior of particles and anti-particles in an attempt to understand why matter overwhelmingly dominates the universe we live in.
Mallik is the principal investigator on the primary particle physics grant. For specific research using the Stanford Linear Accelerator, she receives about $260,000 in annual base funding from the U.S. Department of Energy to better understand why matter, rather than anti-matter, is overwhelmingly present in the universe, even though physicists theorize that the two forms of matter were present in equal amounts when the universe was created. One of the goals of particle physics is to explore the nature of matter, forces, energy and time at the most fundamental level.
She received her doctorate from the City College of New York in 1978, joined the UI faculty in 1988, and is a Fellow of the American Physical Society. From 1998 to 2000, she served as a member of the U.S. High Energy Physics Advisory Panel, which sets research priorities, surveys the peer review process, and advises the U.S. Department of Energy's Director of Science and the National Science Foundation on particle physics research.
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