Leptons At Work

1
Leptons At Work

• Particle Physics Lesson 8

2
Research Task

• some questions to research
• What is a positron?
• Who suggested it must exist?
• Who discovered it?
• What is a muon?
• When was it discovered?
• Who said, Who ordered that?
• What is a neutrino?
• Who suggested it must exist?
• Who discovered it?

3
Todays Objectives

• To learn about lepton conservation rules
• Start practicing questions!

4
Recap

• Baryon Number and Lepton Number Practice
• Particle Classification Exercise - What Am I?

5
Leptons

• There are six particle-antiparticle pairs known. 
  Leptons (Greek light thing or small coins)
  are the smallest of the fundamental particles. 
  They have the following properties
• fundamental particles without structure
• they interact by the weak interaction.  If they
  are charged, they interact by the electromagnetic
  interaction, but NOT the strong interaction.

6
Leptons

• Leptons come in a family of three
• electron electron neutrino lightest
• muon muon neutrino ?
• tauon tauon neutrino heaviest
• Note that each has a corresponding neutrino.

7
Video

• In Search of Giants The Quark Model
• ? Conservation of Q, B L sheet.

8
Muon Decay

• This happens-
• What about this-
• Why?

9
The names of the leptons are
Lepton Name Lepton Symbol Charge Lepton Number
electron e- -1e Le 1, Lµ 0, Lt 0
electron neutrino ?e 0 Le 1, Lµ 0, Lt 0
muon µ- -1e Le 0, Lµ 1, Lt 0
muon-neutrino ?µ 0 Le 0, Lµ 1, Lt 0
tau t- -1e Le 0, Lµ 0, Lt 1
tau neutrino ?t 0 Le 0, Lµ 0, Lt 1
10
Do these happen?
Conservation of Lepton Type Sheet
11
Lepton Notes

• charge and lepton number are conserved in all
  allowed lepton processes.
• There are three categories of lepton number, Le,
  Lµ, and Lt.  Each lepton has a lepton number, 0
  or 1, in each category, and each antilepton has a
  number 0 or -1 in each category.  You need to
  know the lepton numbers.

12
Lepton Notes

• Each particle has an antiparticle
• for the electron, it is the positron,
• the muon the antimuon,
• and the tau, the antitau. 
• We show the anti-particle either by an opposite
  charge (e) or by putting a bar across the
  symbol.