Classification of Particles

Classification of Particles

1. Neutrons are baryons that decay into protons

   • Beta decay= a neutron changes into a proton
     • Happens when there are many more neutrons than protons in a nucleus
       • Or when a neutron is by itself, outside of a nucleus
     • Caused by the weak interaction
   • When neutron decays it forms a proton, electron and antineutrino
   • Electrons and antineutrinos aren't baryons so they have a baryon number B=0
     • Neutrons and protons are baryons so have a baryon number B=1
       • This means that the baryon numbers on both sides are equal to 1 so the interaction can happen

2. Mesons = Pions & Kaons

   • 1. All mesons are unstable and have baryon number B=0(theyre not baryons)
   • 2.Pions are the lightest meson. 3 versions with different charges
   • 3.Kaons are heavier and more unstable than pions, they have a very short lifetime and decay into pions
   • 4.Pions and kaons were discovered in cosmic rays- cosmic ray showers are a source of both particle. You can observe the tracks of these particles with a cloud chamber
   • 5. Mesons interact with baryons via the strong force.

3. Leptons (e.gelectrons and neutrinos) dont feel the strong nuclear force

   • 1. Leptons are fundamental particles and they dont feel the strong nuclear force. They only raelly interact with other particles via the weak interaction
   • 2.Electrons are stable and very familiar but there are other electons like the muon that heavy electrons
   • 3.Muons are unstable and eventually decay into ordinary electrons
   • 4. The electron and muon leptons each come with their own neutrino.
   • 5.Neutrinos have 0 or almost 0 mass and 0 electric charge, they only take part in the in weak interactions

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