Particle Physics - FSU Physics Department

Towards the standard model
Quark Model (Gell-Mann, Zweig, 1964)
• observed SU(3) symmetry can be explained by
assuming that all hadrons are made of “quarks”
• There are 3 quarks: u (up), d (down), s (strange);
• quarks have non-integer charge:
o u 2/3, d -1/3, s -1/3
• baryons are made of 3 quarks:
o p = uud, n = udd, Λ = uds, Σ = uus Ξ = uss,
Ω - = sss
• mesons are made of quark-antiquark pairs:
_ _
_ _
o π + = ud, π - = u d, π 0 = u u + d d, ……..
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