# 2.2.5 Quarks & Antiquarks

### 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

#### Worked Example

A K particle has a strangeness of –1. Determine the quark structure of this particle.

#### Exam Tip

You will not be expected to remember the charge of each quark as this information is provided on the datasheet. So, instead of memorising the charges of anti-quarks too, just remember they are identical but with opposite signs.

### 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

#### Worked Example

Step 1: Calculate the number of protons

The number of protons is from the proton number = 26 protons

Step 2: Calculate the number of neutrons

Number of neutrons = nucleon number – proton number

Number of neutrons = 56 – 26 = 30 neutrons

Step 3: Up quarks in a proton

Protons are made up of uud quarks = 2 up quarks

Step 4: Up quarks in a neutron

Neutrons are made up of udd quarks = 1 up quark

Step 5: Total number of up quarks

26 protons × 2 up quarks = 52 up quarks

30 neutrons × 1 up quark = 30 up quarks

Total number of up quarks = 52 + 30 = 82 up quarks

#### Exam Tip

The quark combinations for protons, neutrons, pions and kaons will be expected to be memorised for the exam.

### Author: Ashika

Ashika graduated with a first-class Physics degree from Manchester University and, having worked as a software engineer, focused on Physics education, creating engaging content to help students across all levels. Now an experienced GCSE and A Level Physics and Maths tutor, Ashika helps to grow and improve our Physics resources.
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