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Chapter 4 Scientific research applications and usage 87

Quarks and Leptons are the building blocks which build up matter, i.e., they are seen
as the “elementary particles” In the present standard model, there are six “flavors” of
quarks. They can successfully account for all known mesons and baryons (over 200). The
most familiar baryons are the proton and neutron, which are each constructed from up
and down quarks. Quarks are observed to occur only in combinations of two quarks
(mesons) and three quarks (baryons). There was a recent claim of observation of
particles with five quarks (pentaquark), but further experimentation has not borne it out.

Quark Symbol Spin Charge Baryon number S C B T Mass*
Up U 1 / 2 þ2 / 3 1 / 3 0 0 0 0 1.7e3.3 MeV
Down D 1 / 2 1 / 3 1 / 3 0 0 0 0 4.1e5.8 MeV
Charm C 1 / 2 þ2/3 1 /3 0 þ1 0 0 1270 MeV
Strange S 1 / 2 1/3 1 /3 1 0 0 0 101 MeV
Top T 1 / 2 þ2 / 3 1 / 3 0 0 0 þ1 172 GeV
Bottom B 1 / 2 1/3 1 /3 0 0 1 0 4.19 GeV(MS)
4.67 GeV(1S)