Thierry Stolarczyk

Cosmic particle hunter

Particles : Quarks, leptons, bosons and... Higgs

An interaction in the CMS detector (LHC, Cern) showing particle tracks as expected from the decay of a Higgs boson ((c) CMS collaboration, 2013. Learn more.)

Other pages on this site

  • The Neutrino, a ghost particle.
  • Gallex, detecting solar neutrinos
  • Nomad, looking at neutrino osicllations
  • Antares, an undersea telescope for cosmic neutrinos.
  • CTA, detecting cosmic very high energy photons.
    • Enrico Fermi
    (1901 - 1954)    		 Wolfgang Pauli
    (1900-1958)

    Fermions : quark and leptons

    Particle physics describes matter from 12 elementary particles, 6 quarks (from characters in a novel by James Joyce) and 6 leptons (from leptos, meaning light in greek). These 12 matter particles are fermions, named after the italian physicist Enrico Fermi. They obey to Wolfgang Pauli's exclusion principle, which forbids two fermions to be simultaneously in the same state at the same position.
    Quarks and leptons are classified each in 3 families, or flavours, of which only the first one is present in ordinary matter. Other quarks and leptons are produced in particle accelerators or within the cosmic rays.

    The tables below show all the quarks and leptons from the standard model of particle physics.

    Three pairs of leptons exist forming three families with a distinct flavour: (e, νe), electron, neutrino-electron; (μ, νμ), muon, neutrino-muon; (τ, ντ), tau, neutrino-tau.

    Only the first flavour can be found in ordinary matter: Electrons gravitate around the protons and neutrons of the nucleus. The neutrino-electron, νe, is emitted during β decays, a kind of natural radioactivity. The neutrino has been the most mysterious particle for a very long time. A fundamental property of the leptons is that, during an interaction, the flavour is unchanged (namely an electron, e, can be associated to a νe, not to a νμ nor to a ντ).

    Leptons

    electron muon (μ) tau (τ)
    neutrino-e (νe) neutrino-μ (νμ) neutrino-τ (ντ)

    The leptons. Each column represents a family (or flavour).
    Drawings : © Th.Stolarczyk-1994

    Quarks

    u (up) c (charm) t (top)
    d (down) s (strange) b (bottom or beauty)

    The quarks. Each column represents a family (or flavour).
    Drawings : © Th.Stolarczyk-1994

    		 Six quarks (u, d, c, s, b, t) exist that form 3 families. Only u and d quarks, the first flavour, are presents in ordinary matter : they combine into protons (u+u+d) and neutrons (u+d+d).

    Satyendranath Bose
    (1894-1074)

    Bosons carry the forces

    Bosons, from the indian physicist Bose that first postulate their existence, can -unlike fermions- be at the same position in the same state. It is the basis of the Laser working principle : the Laser beam consists in photons -that are bosons- in the same state (they have all the same wavelength or energy). In the standard model of particle physics, the 12 matter particles, leptons and quarks, interact between themselves through vector bosons.

    Photon: The photon carries the electromagnetic force; Yes a photon is not an ordinary mattter particle like electron, u and d quarks, although it is part our daily life.
    The bosons named W+, W- and Zo for the weak interaction (responsible for the β radioactivity and the weakness of the interaction of neutrinos with matter)
    Gluon: The gluons (a total of 8) for the strong interaction (responsible for the stability of the nucleus).
    The graviton carries the gravitationnal force (it has not been discovered yet as a particle but gravitationnal waves were discovered in 2015).

    Drawings : © Th.Stolarczyk-1994

    The Higgs boson

    This particle was recently discovered at LHC at CERN. It plays a very special role in the particle physics standard model in giving masses to all other particles.