CIE A Level Physics复习笔记11.2.1 Fundamental Particles

• Quarks are fundamental particles that make up other subatomic particles such as protons and neutrons
• Protons and neutrons are in a category of particles called hadrons
  • Hadrons are defined as any particle made up of quarks
• Fundamental means that quarks are not made up of any other particles. Another example is electrons
• Quarks have never been observed on their own, they’re either in pairs or groups of three
• There are six flavours (types) of quarks that exist:

The six flavours of quarks

• The charge of a hadron is determined by the sum of the charges of its quarks
• Each flavour of quark has a certain relative charge:

Each flavour of quark has a charge of either +⅔e or -⅓e

• 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:

+⅔e + ⅔e - ⅓e = +1e

• The equivalent antiparticle of the quark is the anti-quark
• These are identical to quarks except with opposite relative charges

Each flavour of anti-quark has a charge of either -⅔e or +⅓e. The quark composition of anti-protons and anti-neutrons changes to anti-quarks

• Leptons are a group of fundamental (elementary) particles
• This means they are not made up of any other particles (no quarks)
• There are six leptons altogether:

The six leptons are all fundamental particles

• The muon and tau particle are very similar to the electron but with slightly larger mass
• Electrons, muon and tau particles all have a charge of -1e and a mass of 0.0005u
• There are three flavours (types) of neutrinos (electron, muon, tau)
• Neutrinos are the most abundant leptons in the universe
  • They have no charge and negligible mass (almost 0)
• Leptons interact with the weak interaction, electromagnetic and gravitational forces
• However, they do not interact with the strong force
• Although quarks are fundamental particles too, they are not classed as leptons
• Leptons do not interact with the strong force, whilst quarks do