2.3 - Conservation Laws & Particle Interactions Flashcards
What are the 4 fundamental forces/interactions?
- Gravity
- Electromagnetism
- Strong nuclear (or strong interaction)
- Weak nuclear
What is the weakest of the 4 fundamental forces?
Gravity
What is the strongest of the 4 fundamental forces?
Strong nuclear
What is the range of the weak force?
up to 10⁻¹⁸m.
(an atto-metre)
What are the fundamental interactions in order of strength?
- Strong
- Electromagnetism
- Weak
- Gravity
What do gravitational interactions only affect?
Particles with mass.
What do electromagnetic interactions only affect?
Particles with charge.
What do weak interactions only affect?
They actually affect all particles.
What do strong interactions only affect?
Hadrons (Baryons and Mesons).
When is a virtual/exchange particle created?
When 2 particles exert a force on each other (it is then formed).
What is the reason for an exchange particle?
To carry the fundamental force between each particle in the collision. (this is in a VERY short amount of time)
What are gauge bosons?
Exchange particles that mediate the 4 fundamental interactions.
What are the exchange particles of the strong interaction?
All pions (between nucleons).
What are the exchange particles of the weak interaction?
W⁺, W⁻ bosons.
(also Z⁰ but that’s not in the syllabus)
What are the exchange particles of the electromagnetic interaction?
Photon.
(specifically a gamma photon)
What are the exchange particles of the gravitational interaction?
Gravity is so weak it only has noticeable effects on large masses, so it doesn’t play a part in particle interactions.
What are the 3 main properties of photons?
- no mass
- no charge
- it is its own antiparticle
Draw the Feynman diagram of the electromagnetic repulsion between 2 electrons.
Check online for answer.
(must include electrons going inwards and the virtual photon leave and the electrons going outwards)
What are 2 examples of the weak interaction in action?
B- decay and B+ decay
What is the equation of B- decay?
n -> p + e- + /Ve
neutron decays into a proton and lets out an electron and electron antineutrino
What is the Feynman diagram of B- decay?
Check online.
(don’t forget W- boson as exchange particle)
What is the equation for beta+ decay?
p –> n + e+ + Ve
proton decays into a neutron, positron and electron neutrino
What is the Feynman diagram?
Check online.
(don’t forget the W+ boson as exchange particle)
What is electron capture and what is the equation for it?
Electron capture is a weak interaction.
Electron capture is when an atomic electron is absorbed by a proton in the nucleus.
p + e- -> n + Ve
What is the difference between an electron-proton collision and electron capture?
Electron capture is when an atomic electron is absorbed by a proton in the nucleus and electron-proton collision is when an electron collides with a photon.
They bot have the same equation.
What is the exchange particle of electron capture?
The W- boson.
What is the exchange particle of electron-proton collision?
The W+ boson.
What is the Feynman diagram for electron capture and electron-proton collision?
Check online
(they have different exchange particles btw).
What are the 4 rules of drawing Feynman diagrams? (particle interaction diagrams)
- Incoming particles start at the bottom and move upwards.
- Baryons and leptons can’t cross from one side to the other.
- Charges on both sides must balance. W bosons carry charge from one side to the other.
- W- particles going to the left has the same effect as a W+ boson going to the right.
What are the 6 conservation laws of particle interactions?
- Charge
- Baryon number
- Lepton number
- Strangeness
- Energy (or mass-energy)
- Momentum
