Quarks

Quarks are the fundamental subatomic particles that make up all hadrons.


Types are:

  • Up quarks
  • Down quarks
  • Strange quarks


They have fractional electric charges and baryon numbers:

QuarkChargeBaryon NumberStrangeness
up+23\frac{2}{3}+13\frac{1}{3}0
down-13\frac{1}{3}+13\frac{1}{3}0
strange-13\frac{1}{3}+13\frac{1}{3}-1

Antiquarks

Antiquarks are the antiparticles to quarks with opposite baryon number and strangeness:

NameChargeBaryon NumberStrangeness
anti-up-23\frac{2}{3}−13-\frac{1}{3}0
anti-down+13\frac{1}{3}-13\frac{1}{3}0
anti-strange+13\frac{1}{3}-13\frac{1}{3}+1

Hadron quark compositions

The difference between Baryons and Mesons is the number of quarks that they contain. Baryons contain combinations of 3 quarks or 3 antiquarks.

Example: Proton

The proton contains 2 up quarks and 1 down quark.

Illustration showing a proton with two up quarks and one down quark.
PropertyCalculation
Charge23 + 23−13=+1\frac{2}{3}\text{ + }\frac{2}{3}-\frac{1}{3}=+1
Baryon number13+13+13 = + 1\frac{1}{3}+\frac{1}{3}+\frac{1}{3}\text{ = + 1}

Example: Neutron

The neutron contains 1 up quark and 2 down quarks.

Diagram showing the quark composition of a neutron with one up quark and two down quarks.
PropertyCalculation
Charge23 - 13−13=0\frac{2}{3}\text{ - }\frac{1}{3}-\frac{1}{3}=0
Baryon number13+13+13 = + 1\frac{1}{3}+\frac{1}{3}+\frac{1}{3}\text{ = + 1}

Mesons:

Mesons contain one quark and one antiquark. They have a baryon number of 0.


Example: π+

The π+ meson is comprised of 1 up quark and 1 anti-down quark

Diagram showing a meson composed of one up quark and one anti-down quark.
PropertyCalculation
Charge+23+13 = +1+\frac{2}{3}+\frac{1}{3}\text{ = +1}
Baryon number13+−13 = 0\frac{1}{3}+-\frac{1}{3}\text{ = 0}

Discoveries in particle physics

Predicting existence of quarks and other particles relies on collaborative analysis from large teams (e.g. at CERN).


Confirming predictions cements acceptance of theories like quarks making up all hadrons.


So quarks form the basis for all composite particles feeling the strong interaction. Their properties explain how hadrons gain their mass, charge and stability.

Quarks & Antiquarks

This lesson covers: 

  1. Quarks as fundamental particles combining to form hadrons
  2. The properties of quarks
  3. How antiquarks are the antiparticles to quarks
  4. Examples of quark compositions in protons, neutrons and mesons