Strange Quarks (AQA A Level Physics): Revision Note

Strange Particles

• Strange particles are particles that include a strange or anti-strange quark

• An example of these are kaons

• Strange particles always:

  • Are produced through the strong interaction

  • Decay through the weak interaction

  • Are produced in quark-antiquark pairs

• An example of a kaon production could be:

Kaons are produced through the strong interaction. This is shown by the gluon exchange particle.

• An example of kaon decay could be:

Kaons decay via the weak interaction. This is shown by the W⁺ boson.

Strangeness

• Strangeness, S, like baryon and lepton number, is a quantum number

• Strangeness is conserved in every interaction except the weak interaction

• This means that strange particles are always produced in pairs (e.g. K+ and K–)

• S depends on whether the particle contains a strange quark, anti-strange quark, or no strange quarks

  • Particles with an anti-strange quark have S = +1

  • Particle with a strange quark have S = –1

  • Particles with no strange quark have S = 0

Only particles with a strange quark have a strangeness of +1 or –1

• Strangeness can change by 0, +1 or –1 in weak interactions