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BaBar Experiment Observes CP Violation in B-Decays

College Park, MD - August 3, 2004 - Drs. Hassan Jawahery and Doug Roberts, professors in the University of Maryland Department of Physics, and their colleagues working on the BaBar experiment, have discovered a drastic difference in the behavior of matter and antimatter. In fact, they have discovered the first statistically significant evidence of direct charge parity (CP) violation in B meson decays.

"B meson" refers to heavy particles containing the bottom quark (b). B mesons and anti-B mesons are formed by colliding electrons and their antimatter counterparts, positrons, and then decay in a short time period. CP violation is what occurs when the matter and antimatter decays are counted and the numbers are unequal. In other words, the decay rates are different.

The BaBar scientists used the PEP-II accelerator at the Stanford Linear Accelerator Center (SLAC), a Department of Energy laboratory operated by Stanford University, to collide the electrons and positrons and form millions of B mesons and anti-B mesons. The study of more than 200 million pairs of these particles showed that the anti-B mesons decayed significantly faster.

BaBar, as well as other experiments in the field of particle physics, has observed matter-antimatter asymmetries before. However, this is the first time that direct charge parity (CP) violation has been observed in B decays and used to explain the asymmetric behavior. This result is one integral step to better understanding the matter and antimatter and, in turn, the nature of the world we live in.

"These findings may bring us one step closer to understanding why the universe today consists only of matter when, after the Big Bang, matter and antimatter were both present - and in approximately equal amounts," says Jawahery.

While BaBar is a collaboration of approximately 600 scientists from all over the world, these particular measurements were the focus of the work of Jawahery and his students and research associates since the start of the BaBar experiment. In addition to his current students and research associates, several of his former students and postdoctoral associates are now collaborators from other institutions. For example, Maryland alum Dr. Amir Farbin wrote his thesis on the topic and is now at the University of Chicago. Dr. James Olson, who was a postdoctoral associate under Professor Jawahery, is now an assistant professor at Princeton University and one of the leaders of the analysis of the experiment.

For more information, please visit the following links:

Physical Review Letters journal article:

SLAC Press Release:

University of Maryland Department of Physics

University of Maryland High Energy Physics Group


Contact Information:

Karrie Sue Hawbaker

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