PX156 - H3 - the weak force

charged current (CC)

• bosons: $W^{\pm }$
  • rest mass: $0$
  • electrically charged
  • weak isospin
  • $m_W\approx 80GeV/c^2$ (very heavy)
• the only force that can change flavour
• couples states of different weak isospin
• leptons:
  • have $T_W=\pm 1/2$
  • transform particles from top row to bottom, and vice versa, in the same generation
• quarks
  • have $T_W=\pm 1/2$
  • transform particles from top row to bottom, and vice versa, in same and different generations
    

neutral current (NC)

• boson: $Z^0$
  • neutrally charged
  • $m_Z\approx 90GeV/c^2$
• it cannot change flavour
• decay into any particle-antiparticle pair of the same flavour
  • eg: $Z^0\to l^{+}{l}^{-}$ or $q\overline{q}$ or $\overline{\nu }\nu$

• range:

- where, $R=\frac{\hslash }{m_{W,Z}c}$

• large boson mass $⟹$ exponential term supresses the force at moderate distances
• note: ${\alpha }_{W,Z}\approx 5{\alpha }_{EM}$
  • the 'weakness' of the weak force comes from the mass of the bosons