Quarks and leptons

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  • these are particles and antiparticles which interact through the strong nuclear force (e.g. protons, neutrons, Pi mesons and K mesons)
  • Unlike a particle like an electron, hadrons are NOT fundamental particles because they are made up of smaller particles called quarks.
  • There are two types of hadrons:

1. Baryons - protons and all other hadrons that decay into protons, directly or indirectly

2. Mesons: hadrons that do not decay into protons

* Baryon number - the number of baryons. All baryons have a baryon number of +1. All antibaryons have a baryon number of -1. Particles that aren't baryons are 0

  • muon: (heavy electron) ų, a negatively charged particle with a rest mass 200x of an electron
  • pion: Pi+, Pi- and Pi0. Have a rest mass GREATER than a muon but less than a proton. 
  • kaon: (K meson) can be +, - or neutral with a rest mass GREATER than a pion but less than a proton. they decay through the weak interaction but are created through the strong force
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  • fundamental particles that interact through the weak nuclear force and the EM force if charged.
  • electrons are stable leptons. 
  • muons are heavier, unstable versions of electrons, which eventually decay into electrons or e+
  • these particles each have their own neutrinos, which only take part in weak interaction. 
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Quarks and Antiquarks

  • quarks are fundamental particles: up, down, strange, charm, top and bottom
  • baryons are made up of 3 quarks and anti baryons of 3 antiquarks
  • mesons as made up of quark-antiquark pair. Pions are made up of up, down, anti up and anti down. Kaons are made up of strange quarks as well.

Quark and beta decay:

  • in beta minus decay - a NEUTRON in a neutron rich nucleus changes into a proton, releasing an electron and an electron antineutrino. Quarks: d --> u
  • in beta plus decay - a PROTON in a proton-rich nucleus changes into a neutron, releasing a positron and an electron neutrino.
    Quark confinement: it is not possible to get a quark by itself as blasting a proton etc with energy just gets changed into matter - more quarks and antiquarks
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Conservation rules:

1. Conservation of energy and charge: this applies to any change in science and includes rest energy of particles.

2. Conservation of baryon numbers:

3. Conservation of lepton numbers

4. Conservation of strangeness: this is conserved only in strong interactions. If it isn't conserved then it is a weak interaction.

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Excellent resource thanks!!!!

royby dixon


Short, informative and to the point, it will be very useful for my international students. I like it!

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