Particle Classification

Particle Classification

1. Hadrons

   • Baryons
     • B=1
       • B=-1 for anti-baryons.
     • E.G protons, neutrons
       • Proton is the only stable baryon
         • The neutron will eventually decay into a proton
           • This happens though beta minus decay
     • 3 quarks or 3 anti-quarks
       • Strange if at least 1 quark is strange
         • s=-1 (1strange quark) s=-2 (2 strange quarks)
         • If strangeness is conserved it is mediated by the strong force, if not it is the weak force.
     • Baryon number must be conserved in interactions.
   • Mesons
     • E.G pion, kaon
       • pi +, pi -, pi0
         • Pi + and pi- are antiparticles or each other. pi0 is its own antiparticle.
         • Pions are the lightest meson
       • The kaon is unstable and will decay into 2 pion
     • Quark anti-quark pair
       • If strange quark, its a kaon.
     • B=0
     • Charge and baryon number must be conserved in interactions
     • Short lifetimes
   • Non- Fundamental
     • Feel the strong force
   • Feel all 4 fundamental forces

2. Leptons

   • Fundamental Particles
   • Do not feel the strong force.
   • E.G electron, muon, tau
     • Electron is the only stable lepton
   • Lepton number and charge must be conserved in interactions.
   • Always accompanied by a neutrino