- Either of two subatomic particles in the baryon family, one neutral and one positively charged, with masses of 4,826 and 4,834 times that of an electron and average lifetimes of 3.5 X 10-13 and 9.8 X 10-14 seconds, respectively. See Table at subatomic particle.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.