Quark Composition (CIE A Level Physics)

• Protons and neutrons are not fundamental particles
• They are each made up of three quarks
• Protons are made up of two up quarks and a down quark
• Neutrons are made up of two down quarks and an up quark

 Composition of protons & neutrons

Protons and neutrons are made up of three quarks

• You will be expected to remember these quark combinations for exam questions

• Hadrons are the group of subatomic particles that are made up of quarks
• Hadrons can be either: 
  • Baryons
    • Made up of 3 quarks
  • Mesons
    • Made up of a quark and anti-quark pair

Hadrons

Hadrons may be either a baryon or a meson

• Anti-hadrons can be either:
  • Anti-baryons
    • Made up of 3 anti-quarks
  • Anti-mesons
  • Made up of a quark and anti-quark pair

Anti-hadrons

Anti-hadrons may be either an anti-baryon or an anti-meson

• Note that all baryons or mesons have integer (whole number) charges eg. +1e, -2e etc.
• This means quarks in a baryon are either all quarks or all anti-quarks
  • Combinations of quarks and anti-quarks do not exist in a baryon

would not be a quark combination that exists

• The anti-particle of a meson is still a quark-antiquark pair
• However, the quark becomes the anti-quark and vice versa