Quarks & Antiquarks (AQA A Level Physics)

Properties of Quarks & Antiquarks

Quarks

• The three most common flavours of quarks are: up, down and strange

• The majority of hadrons are made up of different combinations of these quarks

The three main quarks that make up most hadrons

• Each quark has a charge, baryon number and strangeness

• These will be provided on the data sheet

Quarks Table provided on the datasheet

• The charge of a hadron is determined by the sum of the charges of its quarks

• For example, a proton is made up of two up quarks and a down quark. Adding up their charges gives the charge of a proton:

• Equivalently, the baryon number and strangeness of a hadron is determined by the sum of the baryon numbers and strangeness of its quarks

Anti-quarks

• The equivalent antiparticle of the quark is the anti-quark

The three main anti-quarks that make up most hadrons

• These are identical to quarks except with opposite relative charges, baryons numbers and strangeness

Anti-quarks Table

• Quarks have a baryon number of +1/3

• Anti-quarks having a baryon number of –1/3

• Strange quarks have a strangeness of –1

• Anti-strange quarks have a strangeness of +1

  • This is unique to the strange quark

Quark Combinations

Baryons

• 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

Protons and neutrons are made up of three quarks

Mesons

• Pions and kaons are made up of a quark and anti-quark pair

• Pions are either:

  • π⁺ made up of an up quark and an anti-down quark

  • π^– made up on an anti-up quark and a down quark

  • π⁰ made up of an up quark and anti-up quark or down quark and anti-down quark

Pions consist of up and down quarks, and their respective antiparticles, depending on their sign

• Kaons are either:

  • K⁺ made up of an up quark and an anti-strange quark

  • K^– made up on an anti-up quark and a strange quark

  • K⁰ made up of an down quark and anti-strange quark or anti-down quark and strange quark

Kaons consist of up, down and strange quarks, and their respective antiparticles, depending on their sign