The Standard Model

The Standard Model

1. Classifies Elementary particles

   • leptons
     • interact via the weak nuclear force
     • If the lepton has an electric charge it also interacts via the electromagnetic force
     • electron
     • muon
     • tau
     • electron neutrino
     • muon neutrino
     • tau neutrino
     • Anti-leptons
       • positron
       • anti-muon
       • anti-tau
       • electron anti-neutrino
       • muon anti-neutrino
       • tau anti-neutrino
   • quarks
     • Hadrons
       • Made up of quarks
       • Meson = 2 quarks
         • bound by the strong nuclear force
         • Inherently unstable
         • Comprised of a quark and an anti-quark
         • Net 'colour' is always white eg. red quark and anti-red anti-quark
       • Baryon = 3 quarks
         • Net 'colour' is always white e.g. red/blue/green quarks
         • proton = UP, UP , DOWN
         • neutron = UP, DOWN, DOWN
         • Omega minus = STRANGE, STRANGE, STRANGE
     • Anti-quarks
       • Flavour
         • anti-up (û)
         • anti-down
         • anti-strange
         • anti-charm
         • anti-top
         • anti-bottom
       • Charge
         • fractional charge
           • +1/3 e
           • -2/3 e
       • "Colour charge"
         • anti-red (cyan)
         • anti-green (magenta)
         • anti-blue (yellow)
     • Flavour
       • up (u)
       • down (d)
       • strange (s)
       • charm (c)
       • top (t)
       • bottom (b)
     • Charge
       • fractional charge
         • +2/3 e
         • -1/3 e
     • "Colour charge"
       • red
       • green
       • blue
       • has nothing to do with actual 'colour' or actual 'charge'
       • quarks of different colour charge exert an attractive force on one another
     • Interact via the strong nuclear force
   • Elementary particles have no internal structure
   • gauge bosons
     • photon
       • Is its own anti-particle
     • W+, W-
     • Z
     • gluons
   • the Higgs boson
     • known as the 'God particle'
     • Associated with the Higgs field
       • The Higgs field gives mass to fundamental particles
   • All particles have anti-particles
     • Very little anti-matter survived the Big Bang

2. Describes three of the fundamental forces:

   • weak nuclear
     • Responsible for radioactive decay of atoms
     • Mediated by W+, W- and Z^0 particles
   • strong nuclear
     • holds the nuclei of atoms together
     • Strongest of the fundamental forces
     • acts only between quarks within nucleons
       • Only acts over a distance of 1 femtometer (fm) [1x10^-15 m]
       • strength increases as particles get further apart
     • mediated by gluons
   • electromagnetic
     • holds electrons in their atoms, and binds matter together as molecules
     • mediated by photons
     • 2nd strongest fundamental force - approx. 1% of the strong nuclear force
     • Only acts between charged particles
   • Gravity is excluded :(
   • act between bodies of matter
   • are mediated by the exchange of particles (gauge bosons)