AS AQA Phys Unit 1- Quarks

Background

Quarks are fundamental particles which are found in hadrons (baryons and mesons). To make protons and neutrons only two quark types are needed; an up quark (u) and a down quark (d). A strange quark (s) is found in particles which possess the physical property of strangeness. Antiparticles of hadrons are made from antiquarks.

Properties

Antiquarks have opposite properties to quarks:

Quarks

Name: Up Symbol: u Charge: +2/3 Baryon number: +1/3 Strangeness: 0

Down, d, -1/3, +1/3, 0

Strange, s, -1/3, +1/3, -1

Antiquarks

Name: Anti-up Symbol: u (with line on top) Charge: -2/3 Baryon number: -1/3 Strangeness: 0

Anti-down, d (with line on top), +1/3, -1/3, 0

Anti-strange, s (with line on top), +1/3, -1/3, +1

Baryons and quarks

The evidence for quarks came from hitting protons with high-energy electrons. The way in which the electrons scattered showed that there were three concentrations of charge (quarks) inside the proton. Therefore, baryons are always made from three quarks and different baryons have different combinations;

Proton (uud) -Total charge = 2/3 + 2/3 - 1/3 = 1…