![]() ![]() The neutron and all heavier baryons decay directly to protons or eventually form protons, the proton being the least massive baryon. No known decay process or interaction in nature changes the net baryon number. This implies that the mesons, with one quark and one antiquark, have a baryon number B=0. This can be considered to be equivalent to assigning each quark a baryon number of 1/3. Each of the baryons is assigned a baryon number B=1. One of the most important of these is the conservation of baryon number. Nature has specific rules for particle interactions and decays, and these rules have been summarized in terms of conservation laws. Any interaction which is observed can be used to predict other related interactions by "crossing" any particle across the reaction symbol and turning it into its antiparticle. Called CPT invariance, this symmetry plumbs the depths of our understanding of nature.Īnother part of the high energy physicist's toolkit in anticipating what interactions can be expected is " crossing symmetry". ![]() The combination of charge conjugation (C), parity (P) and time reversal (T) is considered to be a fundamental symmetry operation - all physical particles and interactions appear to be invariant under this combination. This approach has been fruitful in helping to determine the rules for particle decay.Ĭonservation laws for parity, isospin, and strangeness have been developed by detailed observation of particle interactions. From this point of view, any decay process which is expected but not observed must be prevented from occurring by some conservation law. This idea is even stated as a principle called the " totalitarian principle" which might be stated as "every process that is not forbidden must occur". Specific quantum numbers have been assigned to the different fundamental particles, and other conservation laws are associated with those quantum numbers.įrom another point of view, it would seem that any localized particle of finite mass should be unstable, since the decay into several smaller particles provides many more ways to distribute the energy, and thus would have higher entropy. Strong overall conservation laws are the conservation of baryon number and the conservation of lepton number. These conservation laws are in addition to the classical conservation laws such as conservation of energy, charge, etc., which still apply in the realm of particle interactions. The study of interactions has led to a number of conservation laws which govern them. In developing the standard model for particles, certain types of interactions and decays are observed to be common and others seem to be forbidden. Particle Interactions and Conservation Laws Particle Interactions and Conservation Laws ![]()
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