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Published by the University of Cincinnati CP group
Hundreds toil
B factories

to find out if CP symmetry is violated in B meson decay

If we look out in space as far as we can see, all evidence says that the universe is made up of nuclear matter - protons, neutrons, and electrons. In the laboratory it is possible to create antimatter (e.g., antiprotons, antineutrons, positrons) which appears to be identical to matter, except that in close contact with matter both can annihilate. This leads to the question: why is our universe a "matter universe" rather than an "antimatter universe," or a universe with equal amounts of each, or nothing?  We now know that fundamental properties of matter (and antimatter) determine how the universe evolves, so there must be a property that somehow causes matter to be preserved over antimatter.  In other words, matter and antimatter do not behave exactly identically.

What is that mysterious property?  At the very least, there must be something we call violation of CP symmetry, also called CP violation or CP asymmetry.  Although it has been known since 1964 that CP violation occurs at a low level (two in a thousand) in the decays of particles known as K mesons, we still don't know what causes it.  According to our current theoretical understanding, it should also occur in the decays of particles called B mesons, rarely but in many distinctive ways.  Its measurement is expected to confirm or refute our interpretation of the particles and forces that we observe.

There is currently a worldwide effort to measure the many manifestations of CP violation expected in decays of B mesons.  Making these measurements requires the production of large numbers of B mesons, and the accelerator facilities designed to generate them have come to be known as "B factories."
Three experiments, involving nearly 1000 physicists, are targeted to make some of the measurements in the next few years and through them study the origin of CP violation.  Several other experiments are in various stages of design.  This page and its linked pages, intended for both general visitors and specialists, provide information and news about the subject of CP violation in B decay and the experiments investigating it.

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