3.2.1.5
Leptons are fundamental particles not made of quarks
Quarks, Leptons & Conservation Laws — AQA A-Level Physics
Key Definition
Leptons — Fundamental particles that do not experience the strong interaction. They are not composed of quarks.
- Leptons include: electron ($e^{-}$), muon ($\mu^{-}$), electron neutrino ($\nu_e$), and muon neutrino ($\nu_\mu$).
- Each lepton has a corresponding antiparticle: positron ($e^{+}$), antimuon ($\mu^{+}$), $\bar{\nu}_e$, $\bar{\nu}_\mu$.
- Leptons have lepton numberA quantum number conserved in all interactions. Leptons (electrons, neutrinos) have lepton number +1, antileptons have -1, and hadrons have 0. $L = +1$. Antileptons have $L = -1$.
- The muon is heavier than the electron and decays into an electron, a muon neutrino and an anti-electron neutrino.
Lepton numberA quantum number conserved in all interactions. Leptons (electrons, neutrinos) have lepton number +1, antileptons have -1, and hadrons have 0. is conserved separately for each generation
- Electron lepton numberA quantum number conserved in all interactions. Leptons (electrons, neutrinos) have lepton number +1, antileptons have -1, and hadrons have 0. ($L_e$): electron and $\nu_e$ have $L_e = +1$; positron and $\bar{\nu}_e$ have $L_e = -1$.
- Muon lepton number ($L_\mu$): muon and $\nu_\mu$ have $L_\mu = +1$; antimuon and $\bar{\nu}_\mu$ have $L_\mu = -1$.
- In any interaction, $L_e$ and $L_\mu$ are separately conserved.
Examiner Tips and Tricks
- Leptons cannot interact via the strong force because they have no quarks.
- They interact only via the weak and electromagnetic (if charged) forces.
Related:Particle Interactions