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Published by the University of Cincinnati CP group
| Hundreds toil
at B factories to find out if CP symmetry is violated in
B meson decay |
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| 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." |
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