13.2.9

Quarks & Antiquarks

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Quarks

Quarks are fundamental particles. Hadrons (including protons and neutrons) are made of quarks. Different combinations of quarks make different hadrons.

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Types of quark

  • There are six different types of quark but you only need to know about the following three:
    • Up, u.
    • Down, d.
    • Strange, s.
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Properties

  • The table summarises the key properties of up, down and strange quarks.
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Antiquarks

  • Every quark has a corresponding antiquark.
    • They have the opposite properties to their quarks.

Quark Combinations - Baryons

Different combinations of quarks form different hadrons. Here we look at two important baryons - protons and neutrons - and their antiparticles.

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Proton

  • A proton is made of two up quarks and one down quark.
    • Proton = uud
  • The charges add up to +1.
    • 23+2313=1\frac{2}{3} + \frac{2}{3} - \frac{1}{3} = 1
  • The baryon numbers add up to +1.
    • 13+13+13=1\frac{1}{3} + \frac{1}{3} + \frac{1}{3} = 1
  • Strangeness and lepton numbers add to zero.
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Antiproton

  • An antiproton is made of two anti-up quarks and one anti-down quark.
    • Antiproton = uud
  • The charges add up to -1.
    • 2323+13=1- \frac{2}{3} - \frac{2}{3} + \frac{1}{3} = -1
  • The baryon numbers add up to -1.
    • 131313=1-\frac{1}{3} - \frac{1}{3} - \frac{1}{3} = -1
  • Strangeness and lepton numbers add to zero.
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Neutron

  • A neutron is made of one up quark and two down quarks.
    • Neutron = udd
  • The charges add up to 0.
    • 231313=0\frac{2}{3} - \frac{1}{3} - \frac{1}{3} = 0
  • The baryon numbers add up to +1.
    • 13+13+13=1\frac{1}{3} + \frac{1}{3} + \frac{1}{3} = 1
  • Strangeness and lepton numbers add to zero.
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Antineutron

  • An antineutron is made of one anti-up quark and two anti-down quarks.
    • Antineutron = udd
  • The charges add up to 0.
    • 23+13+13=0-\frac{2}{3} +\frac{1}{3} + \frac{1}{3} = 0
  • The baryon numbers add up to -1.
    • 131313=1-\frac{1}{3} - \frac{1}{3} - \frac{1}{3} = -1
  • Strangeness and lepton numbers add to zero.

Quark Combinations - Mesons

Different combinations of quarks form different hadrons. Mesons are a type of hadron containing two quarks.

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Pions and kaons

  • Various mesons are created by u, d, s and their associated antiquarks.
  • Pions have u and d quarks (and antiquarks) only.
  • Kaons have one s or s quark.
  • Notice that some pions and kaons are antiparticles of each other.
    • The π0 meson is its own antiparticle!

Jump to other topics

1Physical Quantities & Units

2Measurement Techniques

3Kinematics

4Dynamics

5Gravitational Fields

6Deformation of Solids

7Thermal Physics

8Oscillations

9Communication

10Electric Fields

11Current Electricity

12Magnetic Fields

13Modern Physics

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