Charge conservation elementary charge on positive and negative particles must be extremely close to equal, differing by no more than a factor of 10 for the case of protons and electrons. Ordinary matter contains equal numbers of positive and negative particles, protons and electrons, in enormous quantities. If the elementary charge on the electron and proton were even slightly different, all matter would have a large electric charge and would be mutually repulsive. The best experimental tests of electric charge conservation are searches for particle decays that would be allowed if electric charge is not always conserved. No such decays have ever
Particle decay to further decay. The term is typically distinct from radioactive decay, in which an unstable atomic nucleus is transformed into a lighter nucleus accompanied by the emission of particles or radiation, although the two are conceptually similar and are often described using the same terminology. Particle decay is a Poisson process, and hence the probability that a particle survives for time "t" before decaying is given by an exponential distribution whose time constant depends on the particle's velocity: All data is from the Particle Data Group. Note that this section uses natural units, where formula_4 The lifetime of a particle