Particle Physics and the Standard Model

Fermions (Matter Particles)

Quarks (feel the strong force):

Leptons (don't feel the strong force):

• Electron ($e^-$), electron neutrino ($\nu_e$)
• Muon ($\mu^-$), muon neutrino ($\nu_\mu$)
• Tau ($\tau^-$), tau neutrino ($\nu_\tau$)

Bosons (Force Carriers)

The Higgs boson gives particles mass.

Baryons (3 quarks): proton (uud), neutron (udd) Mesons (quark + antiquark): pion (π), kaon (K)

Baryon Number

• Quarks: baryon number = +1/3
• Antiquarks: baryon number = −1/3
• Baryons: B = +1; Antibaryons: B = −1; Mesons: B = 0

Strangeness

• Strange quark: strangeness = −1
• Anti-strange: strangeness = +1
• Conserved in strong and EM interactions; can change by 0 or ±1 in weak interactions

Always conserved: charge, baryon number, lepton number Conserved in strong/EM (not necessarily weak): strangeness

Beta-minus: $n \to p + e^- + \bar{\nu}_e$ Quark level: $d \to u + e^- + \bar{\nu}_e$ (via W⁻ boson)

Beta-plus: $p \to n + e^+ + \nu_e$ Quark level: $u \to d + e^+ + \nu_e$ (via W⁺ boson)

Photoelectric effect: Light behaves as particles (photons). $E = hf$; work function: $\phi = hf_0$ $\frac{1}{2}mv_{\max}^2 = hf - \phi$

de Broglie wavelength: All matter has a wave nature. $\lambda = \frac{h}{p} = \frac{h}{mv}$

Electron diffraction through thin films proves wave nature of electrons.

• Standard Model: quarks + leptons + bosons
• Baryons = 3 quarks; Mesons = quark + antiquark
• Conserved: charge, baryon number, lepton number
• Weak interaction: changes quark flavour via W/Z bosons
• Wave-particle duality: $\lambda = h/mv$