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.
Answer:
Step 1: Determine the types of quarks in this particle
The kaon is a meson, so is made up of a quark and an anti-quark.
Step 2: Determine the quark that gives a strangeness of −1
The strange quark has a strangeness of −1, so this kaon must include an s quark
Step 3: Determine the quark that gives an overall charge of −1
The kaon has an overall charge of −1
The strange quark has a charge of .
Adding the charges of the quarks together gives the overall charge:
Hence, the missing charge
The anti-up quark () has a charge of
Step 4: State the quark structure of the particle
Strange anti-up =
Examiner 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.