9. The Standard Model of Particle Physics Flashcards
What theory is used to describe the electromagnetic and weak interaction in the standard model?
The electroweak theory
What theory us used to describe strong interactions in the standard model?
Quantum chromodynamics (QCD)
What are the basic constituents of matter?
Quarks and leptons
What is the spin of a quark?
1/2
What is the spin of a lepton?
1/2
Quarks come in _ flavours and _ colours.
6
3
What are the 6 flavours of quark?
Up
Down
Strange
Charm
Top
Bottom
Leptons come in _ types.
6
How do quarks and leptons interact?
Via the spin-1 (gauge) boson
Quarks and leptons are subdivided into _ generations based on ____.
3
Mass
What are the 4 fundamental forces?
- Gravity
- Weak nuclear
- Electromagnetic
- Strong nuclear
How do the 4 fundamental forces act?
By the exchange particles (or force carriers) associated with them.
Which of the 4 fundamental forces is not part of the standard model? Why?
Gravity as it doesn’t have a quantum theory
Rank the 4 fundamental forces from weakest to strongest
- Gravity
- Weak force
- Electromagnetism
- Strong force
What does gravity act between?
All objects with mass
What does the weak force do?
It governs particle decay
What does electromagnetism act between?
Electrically charged particles
What does the strong force do?
Binds quarks together
Which particles experience gravity?
All particles with mass
Which particles experience the weak force?
Quarks and leptons
Which particles experience electromagnetism?
Electrically charged particles
Which particles experience the strong force?
Quarks and gluons
What is the force carrier particle for gravity?
Graviton (not yet observed)
What is the force carrier particle for the weak force?
W+, W-, Z0 (W and Z)
What is the force carrier particle for electromagnetism?
γ (photon)
What is the force carrier particle for the strong force?
g (gluon)
What is the range of gravity?
Infinite
What is the range of the weak force?
Short range
What is the range of electromagnetism?
Infinite
What is the range of the strong force?
Short range
What is a gluon?
A massless force carrier particle with a property called colour confinement.
What does gravity give rise to?
- Newton’s Law
- General relativity
Give the equation for Newton’s law of gravity
F = force
G = gravitational constant
M = mass 1
m = mass 2
r = separation distance
What spin does the (hypothetical) graviton have?
2
What mass does the (hypothetical) graviton have?
0
Where is the weak nuclear force most commonly seen?
Nuclear beta decay
_____________ only interact via the weak force.
Neutrino’s
What spin do gauge bosons (W and Z) have?
1
What mass do gauge bosons (W and Z) have?
Large mass: ~80 GeV/c²
Give the equation that describes how the weak force varies with distance
q = charge
r = separation distance
M_W = gauge boson mass
What does electromagnetism give rise to?
The Coulomb force
Give the equation for the Coulomb force
F = force
K = constant
q = charge
r = separation distance
What is electromagnetism governed by?
Maxwell’s laws
What is the spin of a photon?
1
What is the mass of a photon?
0
A photon is a type of _____ _____.
Gauge boson
What is the purpose of the strong nuclear force?
To keep nucleons bound
Nucleons are made up of ______.
Quarks
What is the spin of a gluon?
1
What is the mass of a gluon
0
Why doesn’t the strong nuclear force have infinite range?
Because quarks and gluons carry a type of charge called colour so are limited to short range by colour confinement.
What spin do fermions have?
1/2
Do fermions obey the Pauli exclusion principle?
Yes
State the 2 main types of fermions
- Leptons
- Baryons (electrons, neutrinos, protons, neutrons)
The fermion wavefunction is ___________ under the exchange of two identical particles.
Anti-symmetric
What spin do bosons have?
Integer
Give one example of a type of boson
Force carriers
The boson wavefunction is _________ under the exchange of two identical particles.
Symmetric
Are all particles in the standard model identical?
Yes
Define quantum field theory
The theory that there is one field for each particle for the entire universe. Particles are (quantized) excitations of this field.
Are leptons bosons or fermions?
Fermions
What are the 6 flavours of lepton?
First generation: electron (e) and electron neutrino (v_e)
Second generation: muon (µ) and muon neutrino (v_µ)
Third generation: tau (τ) and tau neutrino (τ)
What is the charge of an electron?
-1 e
What is the charge of an electron neutrino?
0
What is the charge of a muon?
-1 e
What is the charge of a muon neutrino?
0
What is the charge of a tau particle?
-1 e
What is the charge of a tau neutrino?
0
Which is heaviest: the electron, the muon, or the tau particle?
- Tau
- Muon
- Electron
Are quarks bosons or fermions?
Fermions
What is the charge of a down quark?
-1/3 e
What is the charge of a charm quark?
2/3 e
What is the charge of an up quark?
2/3 e
What is the charge of a bottom quark?
-1/3 e
What is the charge of a strange quark?
-1/3 e
What is the charge of a top quark?
2/3 e
Sort the 6 quark flavours into generations
First generation: d, u
Second generation: s, c
Third generation: b, t
What are the 3 colours of quark?
Red, green, blue
Why can’t free quarks be observed?
Because coloured objects cannot be observed.
What are the two types of colourless states?
Baryons: states with 3 quarks of each of the different colours (red + green + blue = white = colourless)
Mesons: states with 2 quarks with a colour-anticolour quark pair (red+anti-red = colourless)
Which generation of leptons and quarks is most common in nature? Why?
First generation because they are lightest
What charge do gluons have?
0
What charge do photons have?
0
What charge do W± force carriers have?
±1
What charge do Z0 force carriers have?
0
Gluons, photons, W±, and Z0 force carriers are spin-_ _______.
1
Bosons
What force do gluons mediate?
Strong nuclear
What force do photons mediate?
Electromagnetism
What force do W± force carriers mediate?
Weak nuclear
What force do Z0 force carriers mediate?
Weak nuclear
Describe the Higgs Boson (H0)
It is the only spin-0 boson in the standard model. It has no electric or colour charge. Its purpose is to allow W and Z bosons (and other fermions) to acquire mass via the Higgs mechanism.
What is the mass of the Higgs Boson?
125 GeV/c²
All particles have ____-_________ with opposite charge and baryon/lepton/colour/quark flavour number.
Anti-particles
What are hadrons?
Particles composed of quarks
What are the two types of hadron?
- Baryons
- Mesons
How many quarks to baryons have?
3
Give 2 examples of baryons
- Protons
- Neutrons
________ are the only stable baryon.
Protons
How many quarks do mesons have?
2 as a quark/anti-quark pair
Are there any stable mesons?
No, they quickly decay into leptons and photons
Give 2 examples of mesons
- Pion
- Kaon
State the 3 types of pion
State the 3 types of kaon