Elementary Particles

Elementary Particles

Common Properties

  • Mass
    • The mass of a particle is measured in units of energy / (speed of light)2, which per E=mc2 is equivalent to mass 
    • Energy in turn is measured by electron-volts (eV), mega-electron-volts (MeV = 1 million eV), and giga-electron-volts (GeV = 1 billion eV)
    • Common units of particle mass are thus eV/c2, MeV/c2, and GeV/c2
    • For example, the mass of a proton is 938.28 MeV/c2
  • Electric Charge
    • The electric charge of a particle is measured in terms of the elementary charge e, the charge of an electron
    • The charge of a proton, for example, is 1e
  • Spin
    • The spin or angular momentum of a particle is measured in units of h-bar (ℏ) 
    • ℏ = Planck Constant / 2π

Matter Particles

Quarks
  • Six Flavors of Quarks
    • Up Quark = quantum of the Up Quark Field
    • Down Quark = quantum of the Down Quark Field
    • Four heavier, exotic Flavors of Quarks 
      • Charm, Strange, Top, Bottom
  • Six Antiquarks, antimatter versions of the fix flavors of quarks.
  • A proton consists of two up quarks and a down quark
  • A neutron consists of two down quarks and an up quark
  • Murray Gell-Mann coined the word quark, taking it from a passage in James Joyce Finnegans Wake:
    • Three quarks for Muster Mark!
      Sure he hasn’t got much of a bark
      And sure any he has it’s all beside the mark
Leptons
  • Six Flavors of Leptons
    • Electron = quantum of the Electron Field
    • Five exotic flavors of leptons
      • Muon, Tau, Electron Neutrino, Muon Neutrino,Tau Neutrino
  • Six Antileptons, antimatter versions of the six flavors leptons.
    • For example, the antimatter positron is like the electron except for its positive charge.
Properties of Leptons and Quarks
Structure of the Helium-4 Atom

Higgs Boson

  • Peter Higgs postulated the Higgs Field and Higgs Boson in 1964 to account for the masses of the other elementary particles.
  • The Higgs Boson’s lifespan is so short (10-22 seconds) it leaves no tracks in particle detectors.  It’s detected through the tracks of its decay particles, which were observed at the Large Hadron Collider at CERN in 2012.

Exchange Particles

Exchange Particles and Interactions
  • Particles interact by exchanging Exchange Particles (aka Messenger Particles, Force-Carrier Particles, Gauge Bosons).
    • Electromagnetic Interaction
      • Electrically charged particles interact by exchanging Photons
    • Strong Interaction
      • Color-charged particles interact by exchanging Gluons
    • Weak Interaction
      • Particles with half-integer spin interact by exchanging W+, W, and Z0 Bosons
Properties of Exchange Particles

Diagrams