Quarks

Quarks are fundamental particles that make up hadrons. There are six flavours, in three generations:• up (u) and down (d)
• charm (c) and strange (s)
• top (t) and bottom (b)Their charges (in units of e, the charge on a proton):
• u, c and t: +2/3
• d, s and b: –1/3
Every quark has a baryon number of +1/3. Ordinary matter is made of up and down quarks only; the heavier quarks appear in high-energy collisions and cosmic rays.Each quark has an antiquark, written with a bar, e.g. u. An antiquark has the opposite charge and baryon number to its quark: u has charge –2/3 and d has charge +1/3, and every antiquark has baryon number –1/3.Quarks are never observed on their own. This is called quark confinement: they only exist in combinations with a whole-number total charge:
• three quarks (a baryon), or three antiquarks (an antibaryon)
• a quark and an antiquark (a meson)Worked example: find the charge and baryon number of a hadron made of three strange quarks, sss.
charge = (–1/3) + (–1/3) + (–1/3) = –1e
baryon number = 1/3 + 1/3 + 1/3 = 1, so it is a baryon (the omega-minus).