from The American Heritage® Dictionary of the English Language, 4th Edition
- n. An electrically neutral meson having a mass 18,513 times that of the electron and a mean lifetime of approximately 8.0 × 10-20 seconds. See Table at subatomic particle.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. Any of a number of bound states of a heavy quark and its antiquark, especially that formed from a bottom quark and an anti-bottom quark.
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