Quarks and Leptons

Quarks and Leptons

1. Hadrons

   • Are particles that interact through the strong interaction
   • Contains Quarks
   • Examples
     • Protons, Neutrons, Positrons, Pions, and Kaons

2. Leptons

   • Are particles that do not interact through the strong interaction
   • Have no quarks
     • No internal structure
   • Examples
     • Electrons, Positrons, Muons, and Neutrinos

3. Baryons

   • Contain 3 quarks
     • qqq
   • Are hadrons that are protons (or will decay into them)
   • Proton is the only stable baryon
   • Neutrinos are baryons because they decay into protons with a half life of 12 mins
     • Other baryons have a much shorter half life
   • Are also called Fermions

4. Mesons

   • Contain 1 quark and 1 anti quark
     • q q
       • (Anti quark has a flat line above it)
   • Are hadrons that do not include protons in their decay products
   • All mesons are unstable
   • Examples
     • Pions (π Mesons) and Kaons ( K Mesons)
   • Kaons (K Mesons)
     • Are all unstable and decay by the weak interaction
       • Far more slowly than pions
   • Pions (π Mesons)
     • Can be positively, negatively, or un charged
     • Have rest masses between the muon and proton
       • About 300 X the electron
     • Are all very unstable and decay by the weak interaction
       • π positive decays into an antimuon and a neutrino
       • π negative decays into a muon and an antineutrino
       • π uncharged decays into two high energy photons