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Charmed at last.

The "November revolution" of 1974 saw the dramatic discovery by two groups of a new subatomic particle - called either psi or J - that set the stage for wide acceptance of the idea that particies such as neutrons and protons are themselves made up of entities known as quarks. The psi/J particle consists of a charm quark paired with a charm antiquark to form a combination known as charmonium.

Just as a hydrogen atom - which consists of an electron and a proton - has various energy levels, charmonium has a so-called ground state and a number of excited states. In fact, the psi/J particle is actually charmonium in one of these excited states. Over the years, physicists have detected in the debris from electron-positron annihilations nearly all of the possible energy states of charmonium. Now, members of the E760 collaboration at Fermilab in Batavia, Ill., have finally observed charmonium in its fifth energy level - and they did it by sifting through proton-antiproton annihilations.

"This revolutionary technique of creating charmonium particles by proton-antiproton annihilations is also being used by the E760 collaboration to study the properties of other charmonium particles with unprecedented precision," says theorist Eric Braaten of Northwestern University in Evanston, Ill. Braaten recently contributed to theoretical work that makes possible the calculation of charmonium lifetimes consistent with the results of the E760 experiment.
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Title Annotation:charmonium observed at fifth energy level
Publication:Science News
Article Type:Brief Article
Date:Jan 9, 1993
Words:224
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