Particle Physics & The Standard Model Cheat Sheet

Key Facts

• Matter particles are fermions, and each fermion has spin $\frac{1}{2}$.
• Quarks have fractional electric charges of $+\frac{2}{3}e$ or $-\frac{1}{3}e$, while leptons have charges of $-e$, $0$, or $+e$ for antiparticles.
• A proton is made of quarks $uud$, so its charge is $+\frac{2}{3}e + \frac{2}{3}e - \frac{1}{3}e = +e$.
• A neutron is made of quarks $udd$, so its charge is $+\frac{2}{3}e - \frac{1}{3}e - \frac{1}{3}e = 0$.
• The photon $\gamma$ carries the electromagnetic force and has charge $0$ and rest mass $0$.
• The strong force is carried by gluons, and it binds quarks together inside protons, neutrons, and other hadrons.
• The weak force is carried by $W^+$, $W^-$, and $Z^0$ bosons, and it can change one type of quark or lepton into another.
• In particle reactions, total electric charge, total energy, total momentum, and total baryon number must be conserved.

Vocabulary

Standard Model

The Standard Model is the theory that classifies known elementary particles and describes the electromagnetic, weak, and strong interactions.

Fermion

A fermion is a matter particle with spin $\frac{1}{2}$, including quarks and leptons.

Boson

A boson is a force-carrying particle, such as the photon $\gamma$, gluon $g$, $W^+$, $W^-$, $Z^0$, or Higgs boson $H$.

Quark

A quark is an elementary particle that combines with other quarks to form hadrons such as protons and neutrons.

Lepton

A lepton is an elementary particle that does not feel the strong force, such as the electron $e^-$, muon $\mu^-$, tau $\tau^-$, and neutrinos.

Antimatter

Antimatter is made of antiparticles that have the same mass as their matching particles but opposite electric charge and other opposite quantum numbers.