Particle Physics- Unit 1 Flashcards
What is specific charge?
Total charge÷Total mass
Isotope definition
An atom with the same number of protons but a different number of neutrons
Specific charge units
Ckg^-1
Why must teams of scientists collaborate for advances to be made?
Results of experiments must be peer reviewed before they’re confirmed
Particle accelerators are expensive so collaboration helps spread the cost
Many skills and disciplines required
4 fundamental forces
Gravity
Electromagnetic
Strong nuclear
Weak nuclear
What does the strong nuclear force do?
Hold the nucleus of atoms together because gravity is too weak at this scale.
Is also responsible for decay/creation of particles
What does the weak nuclear force do?
Responsible for the decay/creation of atoms
What does the electromagnetic force do?
All objects with charge are repelled or attracted to eachother
What does gravity do?
All objects with mass are attracted to eachother
What is 1 femtometer in meters
1x10^-15
What happens to the SNF is nucleons are 0-0.5 fm apart
It is repulsive
What happens to the SNF if nucleons are 0.5-3 fm apart
It is attractive
What happens to the SNF beyond 3 fm?
No effect
When does beta minus decay occur?
When a nucleus is neutron rich(has too many neutrons)
When does alpha decay occur?
Unstable nucleus
-Too much mass
-Too much energy
-Imbalance of protons/neutrons
What is produced in beta minus decay?
Anti neutrino
What is the energy of a photon directly proportional to?
It’s frequency
What property is the same in a particle and it’s corresponding antiparticle?
Mass
What happens when matter and antimatter meet?
They annihilate
What energy is released in annihilation?
The rest energy(energy stored in the mass of the matter/antimatter)
How many joules in one electronvolt
1mev=1.6x10^-19 J
Mega prefix
10^6
What is pair production
A high energy photon converts it’s energy into a particle and corresponding antiparticle pair
What is needed for a photon to produce a particle and an antiparticle?
It’s energy at a minimum must equal the rest energies of the 2 particles produced
The more energetic the photon:
-Heavier particles produced
-Particles with extra kinetic energy
-Lots of smaller particles
How are the photons emitted after annihilation?
They are emitted in opposite directions to conserve momentum
What’s the difference between baryons and mesons?
Baryons are made of 3 quarks
Mesons are made of a quark and an antiquark
Hadrons vs leptons
-Hadrons feel the SNF, leptons can’t
-Hadrons can be broken up into quarks whereas leptons are fundamental
What’s the only stable hadron?
Protons
What’s the only stable lepton?
Electrons
What’s a muon?
A big unstable electron
4 meson rules to find quark composition of a meson
-Must contain a quark + antiquark
-Charge must add up to +1,-1,0
-If strangeness=0 - - > pion
-If strangeness≠0 - - > Kaon
What is always conserved?
Charge
Baryon number
Lepton electron number
Lepton muon number
Strangeness(Strong interaction)
Exchange particle of electromagnetic force
Virtual photon
Exchange particle of weak nuclear force
W+ and W- bosons
Exchange particle of strong nuclear force
Pions if force between nucleus
Gluons if force between quarks
Feynman diagram rules
Before interaction at bottom
After interaction at top
Baryons on the left
Leptons on the right
Range of weak nuclear force
Very short
Range of strong nuclear force
3fm
Range of gravity
Infinite
Range of electromagnetic force
Infinite
How is the nucleon number calculated.
Is it calculated from the different isotopes that exist for each element
What quark transformation happens in beta minus decay
Down quark becomes up quark
How does the weak nuclear force operate
It used w+ or W- bosons or conserve energy/momentum
Proton quark composition
Uud
Neutron quark composition
Udd
Why do SNF and wnf have short ranges?
The mass of these large exchange particles require large amounts of energy to be borrowed (to create it). Meaning, it only exists for a short time and hence had a short range.
Why must the strong nuclear force be repulsive at small separations?
If it wasn’t it would crush nucleus to a point
Range of alpha particles
Short range in air
How were neutrinos hypothesised?
-Experiments showed the energy of particles after Bega decay was less than before
-Wolfgang Paulo suggested another particle was emitted too which carried the missing energy
-Had to be neutral to conserve charge
-Observed 25 years later
What is the minimum energy for pair production
Total rest energy of the particles produced
Quark confinement
It’s not possible to get a quark by itself
When is strangeness always conserved?
When is it sometimes conserved?
Always: Strong interaction
Sometimes: Weak interaction
How do mesons interact with baryons?
Via the strong force
How are strange particles created and decayed?
Created via strong interaction
Decayed by weak interaction
Kaons
Kaons are heavier and more unstable than pions
Short lifetime
Decay into pions
Name the particle believed to be responsible for mass
Higgs boson
Name the particle that is difficult to detect
Anti neutrino
Beta minus decay exchange particle
W- boson
Exchange particle definition
Force carrier for the 4 fundamental forces
Explain why there is a minimum energy for a photon to do pair production
Because the photon needs to provide enough energy to provide for the rest mass
Explain why there is a minimum energy for pair production
Energy of photon just provide at least the rest masses of the particle and antiparticle
How to calculate frequency of annihilation
Find the energy first
Then you need to divide this by 2
Because there are 2 photons
Role or exchange particles
-Transfer energy
-Transfer momentum
-Transfer force
Why are 2 photons produced in annihilation?
momentum must be conserved
so need two photons travelling in different direction
How do we know if an interaction is WNF?
-Strangeness not conserved
-Decay
electron capture and electron-proton collision equation
p+e- -> n + ve
Electron capture exchange particle
W+ boson
Electron proton collision exchange particle
W- boson
