The Quarks

	
Charge:  +2/3    -1/3  
          up     down
          charm  strange
          top    bottom

(The lightest quarks are at the top, and the most massive at the bottom of each column. The corresponding antiquarks have the same masses as their "twins", but their electric charges have the opposite sign.)

Quarks are the building blocks of all the particles of matter except the leptons. They form the well known proton and neutron, and a host of other short- lived particles that have been discovered during the past 50 years.

Quarks have a striking property: their electric charges are a fraction of the "standard" amount of charge, as carried by the electron or proton. However, they combine only in ways that lead to whole unit charges (or no charge) in their composites.

Quarks form only two kinds of composites:

  1. Baryons are formed by groups of three quarks or three antiquarks. Protons are baryons, formed by two up and one down quark. (A proton's electric charge is +2/3 + 2/3 - 1/3 = 1.) Neutrons are baryons, formed of one up and two down quarks (charge = 0). An antiproton is a baryon composed of one down and two up antiquarks, giving a net charge of +1/3 - 2/3 - 2/3 = -1.
  2. Mesons consist of one quark combined with one antiquark, and they may carry a charge of +1 or -1 or 0, depending on the quarks involved. This antimatter- matter combination is very unstable, so mesons usually last for only a few billionths of a second before breaking down into lighter particles and/or energy. Lightest is the pi-meson or pion (pi), composed only of a combination of up and down quarks or antiquarks, and produced abundantly at TRIUMF. Its mass is about 1/7 that of a proton. The kaon is another meson. A kaon always contains a strange quark or antiquark, and it has half a proton's mass.

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