Conservation Rules

Every particle interaction must obey a set of conservation rules. Checking these is how you decide whether a proposed interaction or decay can happen.Energy (including rest energy), momentum and charge are conserved in all interactions. The total charge before must equal the total charge after.Baryon number is always conserved. Baryons have B = +1, antibaryons B = -1, and mesons and leptons B = 0. Lepton number is also always conserved, and electron lepton number and muon lepton number must be conserved separately.Strangeness is conserved in strong interactions, which is why strange particles are always produced in pairs. In weak interactions strangeness can change by 0, +1 or -1, which is how a kaon decays into particles with no strangeness.To test an equation, add up charge, baryon number, lepton number and strangeness on each side. For example, in p + p → p + p + π⁰ charge is +2 on both sides and baryon number is 2 on both sides, so the interaction is allowed.