7. Weak Interaction Phenomena Flashcards
What does the parity operator P do?
Changes signs of all the components of the three vectors in the system
What is a consequence of a system being symmetrical under parity wrt its handedness?
If it is symmetrical under P, you cannot distinguish between the LH and RH coordinate systems
- The equations governing the system are the same in either coord system and vv
What are the eigenvalues of the parity operator P and when is it conserved?
Eigenvalues of +1 and -1
It is conserved when the description is symmetrical
What does the charge conjugation operator C do?
Interchanges particles with anti particles
What is a consequence of a system being symmetrical under charge conjugation
Cannot distinguish between particles and anti particles and vv
What are the eigenvalues of the charge conjugation operator C and when is it conserved?
Eigenvalues of +1 and -1
It is conserved when the description is symmetrical
Which fundamental forces are conserved by the C and P operators?
Strong and EM conserve C and P
Weak does not due to its V-A structure
Describe what was observed in the experiment which exhibited the weak interaction violating parity
Used a polarised sample of cobalt and in beta decay, the electrons were emitted preferentially in teh direction opposite to the spin polarisation
- Maximally violated
Describe what is meant by maximal parity violation, and how this is calculated
Calculates N(↓) - N(↑) / N(↓) + N(↑)
- N(↓) is the number of electrons emitted in the opposite direction of polarisation
- N(↑) is the number of electrons emitted in the parallel direction of polarisation
- Calcualted to be +1 for the WI parity violation which is the max number
What does the C symmetry imply about the decay rate
The particle decay rate is equal to the anti particle decay rate
What does the CP symmetry imply about the total rate of a process
The total rate for a process (decay or interaction) is equal to the total rate of the anti process
What does CP violation allow you to distinguish between
Matter and anti matter and LH and RH
What is the CP symmetry of the universe?
CP asymmetric as the observed universe is made of matter
How is CP related to the BB
It is thought that the U contained equal amounts of matter and anti matter
- CP would have been necessary to eliminate all the anti matter while retaining a tiny portion of matter
How is CP related to the BB
It is thought that the U contained equal amounts of matter and anti matter
- CP would have been necessary to eliminate all the anti matter while retaining a tiny portion of matter
What are the three Sakharov conditions
- A baryon number violating process existed, so the total U baryon number could change
- C and CP violating processes were taking place. This means the baryon number violating process affects baryons and anti baryons at different rates
- Processes forwards wouldn’t equal processes backwards as the U is out of thermal equilibrium
Which of the C,P,T operators are unitary?
C and P are
T is not
Describe what the T operator does and how it is different to the C and P operators
The T operators reverses the time direction of the theory
- As it is not unitary it does not result in a conservation law
Describe what happens to parameters under the T operator
Momenta, spins change sign
- complex scalars in the Lagrangian or Hamiltonian become complex conjugated
What is the CPT theorem and state the two consequences of it?
CPT symmetry is respected in any QFT which is local, unitary and Lorentz invariant
- Consequences are that mass and lifetime of a given particle is equal to the antiparticle
Describe how we can test for CP and T symmetry violations
Neutral meson oscillations
- The probability of a meson to oscillate into its antiparticle and reverse process are related by both CP and T symmetries
- They have different probabilities
What are penguin diagrams?
A one loop process where a quark temporarily changes flavour and this quark engages in a tree interaction
Describe why we can see FCNCs in penguin diagrams
They are forbidden in tree diagrams, but can appear rarely in loop diagrams, such as penguin diagrams
What are box diagrams?
Second order weak interaction (flavour changes by 2 units)
- Transitions between meson particles and anti particles
Does strangeness commute with the Hamiltonian?
No as it does not conserve flavour
What is the intrinsic parity of a pion?
-1
