Leptons At Work

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Leptons

  • The other type of matter particles are the leptons
  • There are 6 leptons: Three have electrical charge and three do not.
  • They appear to be point-like particles without internal structure
  • They are fundamental particles (cant be broken down into anything smaller)

Charged Leptons

  • Muon
  • Electron
  • Tau [Don't need for A Level]

Uncharged Leptons

  • Muon-neutrino
  • Electron-neutrino
  • Tau- Neutrino

The neutrinos have no charge and no mass so they are hard to find.

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Antiparticles

  • For each lepton there is a corresponding antimatter antilepton.
  • Named as you would expect (antitau and antimuon)
  • Except for the antielectron which is called a positron
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Lepton Decays

  • The heavier leptons, taus and muons are not found in ordinary matter
  • They quickly decay or transform into higher leptons
  • Sometimes they even transform into quarks
  • Electrons and the 3 tpes of neutrinos are all stable
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Lepton Type Conservation

  • Electron number, muon number and tau number refer to the family
  • Electrons and their neutrinos have an electron number of +1
  • Electrons have an electron number of +1
  • Electron neutrinos have an electron number of +1
  • Positrons have an electron number of -1
  • Antielectron neutrinos have an electron number of -1
  • This structure above is followed by Muons and their Muon Number as well as Taus and their Tau Number.
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Conservation Laws

  • Lepton number is always conserved
  • Electron number, muon number and tau number are also always conserved
  • Take an example: A muon decays into a muon-neutrino and an electron and an antielectron-neutrino

m num: (+1) -> (+1) + (0) + (0) <- Conserved 

e num: (0) -> (0) + (+1) + (-1) <- Conserved

l num: (+1) -> (+1) + (+1) + (-1) <- Conserved

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Lepton Number

  • We described lepton number as a means of categorising leptons
  • Just as with baryon nmber, lepton number is conserved
  • This explains why leptons are always formed from non-leptons in pairs as one lepton and one antilepton
  • An antilepton is created with a neutrino of the same generation
  • All leptons have a lepton number of +1
  • All antileptons have a lepton number of -1
  • Everything else has a lepton number of 0
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