Particles

Particles

1. Quarks

   • Baryons consist of 3 quarks
     • Proton = uud
     • Neutron = udd
   • Mesons consist of a quark and and antiquark pair
   • Quarks are fundamental particles

2. Particles and Antiparticles

   • Every particle has a matching antiparticle that has the same mass and rest energy but the opposite charge
     • Proton = +1 Antiparticle = -1
     • Electron = -1 Positron = +1
     • Neutrino = 0 Antineutrino = 0
   • Annihilation is when a particle and an antiparticle collide and destroy each other
     • All of the mass is converted into the energy of TWO PHOTONS
       • Two photons are necessary to ensure both energy and momentum are conserved
   • Pair production happens when when one proton has enough energy and splits into a particle and an antiparticle pair
     • The minimum energy for a photon to undergo pair production is the total rest energy of the particles produced
       • Usually you get electron-positron pairs produced because they have a low mass

3. Forces

   • Strong nuclear
     • Attractive from 0.5fm to 3-4fm Repulsive from less than 0.5fm
     • Acts only on HADRONS
     • Exchange particle = GLUON
   • All forces are caused by the exchange of particles
   • Gravity
     • Is only attractive
     • Exchange particle = GRAVITON
   • Weak Nuclear
     • Change the 'flavour' of quarks E.g. causes beta decay
     • Affects all particles
     • Exchange particle = W BOSON (W+, W-)
   • Electromagnetic
     • Is only attractive
     • Exchange particle = VIRTUAL PHOTON

4. Particle interactions

   • Charge is always conserved
   • Baryon number is always conserved
   • Strangeness is always conserved in strong interaction
   • Lepton number is always conserved

5. Radiation

   • Beta minus = a NEUTRON into a PROTON Accompanied by the emission of an anti-neutrino
     • The existence of the neutrino is to account for the conservation of energy
   • Beta plus = PROTON into a NEUTRON
   • An alpha particle is a helium atom with TWO PROTONS and TWO NEUTRONS.
   • Gamma ray has NO PROTONS and NO NEUTRON