Charge, Baryon Number and Lepton Number

To apply the conservation laws you need three numbers for every particle.Charge (Q), in units of e: proton +1, neutron 0, electron −1, positron +1, neutrinos 0, π⁺ +1, π⁰ 0, π⁻ −1.Baryon number (B): every baryon (proton, neutron) has B = +1 and every antibaryon has B = −1. Each quark has B = +1/3 and each antiquark −1/3, so mesons (quark + antiquark) have B = 0. Leptons and photons have B = 0.Lepton number (L): every lepton (e⁻, μ⁻, τ⁻ and their neutrinos) has L = +1 and every antilepton (e⁺, antineutrinos) has L = −1. Hadrons and photons have L = 0. Strictly, electron, muon and tau lepton numbers are each conserved separately.An antiparticle always has the opposite charge, baryon number and lepton number to its particle. A photon has zero for all three.Worked example: is β⁺ decay, p → n + e⁺ + ν_e, allowed by these laws?Q: +1 → 0 + 1 + 0 = +1 ✓B: +1 → +1 + 0 + 0 = +1 ✓L: 0 → 0 + (−1) + (+1) = 0 ✓All three are conserved. (A free proton does not actually decay this way, because energy would not be conserved; inside a nucleus the energy can be supplied.)