Definition of "pion" []

• A semistable meson produced either in a neutral form with a mass 264 times that of an electron and a mean lifetime of 8.4 × 10-17 seconds or in a positively or negatively charged form with a mass 273 times that of an electron and a mean lifetime of 2.6 × 10-8 seconds. Also called pi meson. See Table at subatomic particle. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "“The pion is usually pictured as a relatively simple system consisting of one quark and one anti-quark,” Dr. Huber says."
• "This is known as pion punch-through and gives a fake muon signal."
• "This means that a diagram with several interactions will give a larger contribution than the naive one with the exchange of only one pion, which is the one though that does gives a rough picture of the scattering of two protons."