Chapter 2 - Quarks and Leptons Flashcards
How are cosmic rays a source of high energy particles?
Cosmic rays are fast-moving protons or small nuclei. They collide with gas atoms in the atmosphere, creating showers of particles and antiparticles that can be detected by ground level
How can cosmic ray showers be detected?
- Use of two geiger counters placed one above the other, separated by absorbing lead.
- If both counters detect radiations simultaneously then it’s most likely that a particle from a cosmic ray shower has been detected
What 2 classifications are particles put in?
Hadrons and leptons
What are hadrons?
Particles + antiparticles that interact through the strong interaction.
- Interact through all 4 fundamental interactions (if charged)
What are leptons?
Particles + antiparticles that don’t interact through strong interaction
What are the basic properties of hadrons and leptons?
Hadrons - strong and heavy
Leptons - weak and light
What 2 groups are hadrons split into?
Baryons and mesons
What are baryons?
Protons and all the other hadrons that decay into protons, directly or indirectly
What are mesons?
Hadrons that do not include protons in their decay products
- kaons and pions
Are hadrons fundamental particles?
No their made of quarks (composite)
Why don’t protons decay?
It’s stable
What are the rules for baryon number?
- Total baryon number in any particles interaction never changes
- Proton and the neutron (and all other baryons) have baryon number +1
- Antibaryons have a baryon number -1
- Other particles have baryon number 0
What are the 4 fundamental interactions?
- gravitational interaction
- electromagnetic interaction
- strong interaction
- weak interaction
Which particle doesn’t decay into another?
Neutrino and proton
What is a pion?
The pion or pi meson, is a particle which can be positively charged (pi+), negatively charged (pi-) or neutral (pi0) and has rest mass greater than a muon but less than a proton
What do mesons do?
Interact with baryons via the strong force
What is the exchange particle for the strong nuclear force?
Pion
What do kaons decay into?
Pions
Are leptons fundamental particles?
Yes
Name the leptons
Electrons(e-), positron(e+), muon, antimuon, electron neutrino, electron antineutrino, muon neutrino, muon antineutrino
What are muons?
Muon is a negatively charge particle with a rest mass over 200x the rest of an electron
State the rules of lepton number
- lepton - lepton number +1
(electron and muon lepton number counted separately - antiparticle have lepton number -1
- electron and muon lepton number must be conserved
What does a muon decay into?
Electron
What are strange particles?
Particles that are created via the strong interaction and decay through the weak interaction
What is a kaon?
Kaon or k meson; which can be positive (k+), negative (k-) or neutral (k0) and has a rest mass greater than a pion but still has less than a proton
Why are the strange particles always created in pairs?
Strange particles created via strong interaction, in which strangeness is conserved - so strange particles can only be created in particle - antiparticle pairs
What do strange particles decay by? What is significant in this?
Weak interaction
strangeness is not conserved (can change by +1, -1 or 0)
What are conserved in particle interactions?
Energy and momentum
What are the 4 particle numbers to think about in particle interactions?
Baryon number, lepton number, charge and strangeness
What are quarks? What types of quarks are there?
- Fundamental particles that are building blocks of hadrons
- Up, down and strange and their antiquarks
Why does a proton have a +1 charge?
Overall charge of quarks that make it up have an overall charge of +1
What are he charges and baryon number of 3 quarks?
up - charge: +2/3 baryon number: +1/3
down: charge: -1/3 baryon number: +1/3
strange charge:-1/3 baryon number: +1/3
What is the quark composition of baryons?
Made up of 3 quarks
What is the quark composition of a proton and a neutron?
proton - uud
neutron - udd
What is the quark composition of meson?
- one quark and 1 antiquark
What is the quark composition of a pion and a kaon?
pion - combination of up, down, antiup and antidown quarks. pi- - du^ pi+ -ud^ and pi0 - uu^ or dd^.
kaon - addition of strange particle k- - su^ , k+ - us^ and k0 - ds^ or sd^
What happens in terms of quark’s character in beta minus and plus decay?
minus - d turns into u
plus - u turns into d
Give some characteristics of a strange particle that makes it different from a particle that is not strange
- Contains a strange quark
- Shorter half life than expected
- Decays via weak interaction
Which interaction allows quark flavour/character to be changed?
Weak interaction
