1.4 Hadrons and Leptons Flashcards
What is a hadron?
Particles that feel the strong nuclear force
What are the two types of hadrons?
Baryons and mesons
Are hadrons fundamental particles?
No, they are made up of quarks
What particles are baryons?
Protons, neutrons and others with 3 quarks
Are baryons unstable?
All baryons apart from a free proton can be unstable, so all decay to become other particles. Every baryon eventually decays into a proton
What are antibaryons?
The antiparticles of protons, neutrons and other baryons are antibaryons.
Does baryon number have to be conserved?
Total baryon number in any particle interaction never changes
What is the baryon number of baryons, antibaryons and other particles?
Baryon number is just the number of baryons:
- baryons have a baryon number of +1
- antibaryons have a baryon number of -1
- other particles have a baryon number of 0
What type of force is beta decay caused by?
The weak interaction
What is beta positive decay?
A proton decays into a neutron, positron and electron neutrino
What are mesons?
A type of hadron with two quarks. They interact with baryons via the strong force.
Are mesons stable?
All mesons are unstable
What are the types of mesons?
Pions, kaons and other mesons
What are pions?
- the lightest mesons
- they are the exchange particle of the strong nuclear force
What are kaons?
- heavier particles than pions
- more unstable than pions
- they have a short lifetime and decay into pions
What are cosmic ray showers?
High energy particles from space called cosmic rays interact with particles in the atmosphere and produce ‘showers’ of high energy particles
How do you observe the tracks of cosmic ray showers?
With a cloud chamber
How can you detect cosmic ray showers?
Use two Geiger counters placed one above the other, separated by absorbing lead. If both counters detect radiation simultaneously, then it’s very likely that a particle from a cosmic ray shower has been detected.
What are leptons?
Leptons are fundamental particles which don’t feel the strong force
What are the types of leptons?
Electrons, muons and taus and their neutrinos
Which leptons are the most stable?
Electrons are stable leptons, muons are heavier and more unstable.
What do muons decay into?
Electrons
What type of interactions do neutrinos take part in?
Neutrinos only take part in the weak interaction as they have zero mass and zero electric charge.
What is lepton number?
The number of leptons
What is the lepton number of electrons, muons, taus, their neutrinos and their antiparticles?
- electrons, muons and taus have lepton numbers of +1
- their neutrinos have lepton numbers of +1
- positrons, antimuons and antitaus have lepton numbers of -1
- other particles have lepton numbers of 0
What are the types of lepton number?
- electron lepton number (+1 for electrons and electron neutrinos)
- muon lepton number (+1 for muons and muon neutrinos)
- tau lepton number (+1 for taus and tau neutrinos)
Is lepton number conserved?
Both baryon number and all of the types of lepton number must be conserved in all particle interactions
