pion

[pahy-on]
noun Physics.
the first meson to be discovered: it has spin 0 and may be positively or negatively charged or neutral; charged pions decay into a muon and a neutrino or antineutrino. Symbol: π
Also called pi meson.


Origin:
1950–55; pi (meson) + -on1

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World English Dictionary
pion or pi meson (ˈpaɪɒn)
 
n
physics a meson having a positive or negative charge and a rest mass 273.13 times that of the electron, or no charge and a rest mass 264.14 times that of the electron
 
[C20: from Greek letter pi1 + on]
 
pi meson or pi meson
 
n
 
[C20: from Greek letter pi1 + on]

Collins English Dictionary - Complete & Unabridged 10th Edition
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American Heritage
Science Dictionary
pion   (pī'ŏn')  Pronunciation Key 
A meson occurring 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. The pion was once believed to be the particle that mediates the strong force, which holds nucleons together in the nucleus; it is now believed that the gluon is the mediator particle. Pions do interact with nucleons, however, and are able to transform neutrons into protons and vice versa. Also called pi-meson. See Table at subatomic particle.
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Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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American Heritage
Abbreviations & Acronyms
pion
pi-meson
The American Heritage® Abbreviations Dictionary, Third Edition
Copyright © 2005 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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Example sentences
Place subatomic particles-pion or muons-on one side of the light cylinder, and a particle detector on the other side.
And then the lambda decays into a negative pion and a proton.
The time-reversed movie shows a pion and a deuteron colliding and producing two protons.
When physicists first observed the pion in cosmic ray experiments, they were puzzled.
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