Lectures 11-15 Flashcards
Describe the CPLEAR Experiment
proton anti-proton collisions produces K_0 which will eventually mix, can know from decay products of pion. Measurement may be expressed as (unmixed - mixed) / (unmixed + mixed) - Asymmetry. Depends on cos(delta_M t). Asymmetry graph looks like eloctromagnetic repulsion.
What is the Fitch & Cronin Experiment?
In 1964, Discovered K_long -> two pions. Expected zero. Used a long decay volume, where all K_short could decay. Two axes for detection, collimator, then helium bag then two axes to detect pipi or pipipi.
What are the two possible explainations for CP violation?
1) - Indirect CP violation - K_L and K_S not equivalent to eigenstates K_1 and K_2. Modified by e ~ 2e-3.
2) - Direct CP violation - K_L = K2, which may decay to both CP even and CP odd eigenstate.
It is thought both contribute, however, Indirect CP dominates.
Thinking of Wolfrenstein Parametrisation, where does CP violation orginate from?
WP can be drawn as a triangle. Area of triangle (hence angles) determines the level of CP violation.
What are the three triangles involved in CP violation for the Kaon, B_s and B_d decays?
Kaon - 2nd row 1st column
B_s - 3rd row 2nd Column
B_d - 3rd row 1st column.
Remember matrix and can deduce these.
How is CP violation measured with B_d meson decays?
How are the required particles for this produced?
B_heavy and B_light have almost the same lifetimes, cannot wait certain length of time to allow either to decay. Instead, Produce copius amounts of B_0 B_0_bar pairs, and measure decays to the same final state.
The difference between B_0 and B_0_bar decay rates imply CP violation. This is due to interference between the direct decay and mixing.
The golden Channel to measure this is B_0(bar) - > J/psi K_s.
Can measure the asymmetry of this event. Sensitive to the unitary mixing angle beta. and sin(delta_m).
B_0(bar) pairs are produced using asymmetric electron-positron colliders, so that the Y(4S) is moving in the lab frame, to allow for B decay time measurements.
They Propagate as a coherent pair until one B decays.
What is time-dependent CP asymmetry?
This is to do with B_0/B_0_bar decays. Can measure tag of decay and hence the distance travelled before the other one decays. The sign of the tagged decay causes different delta_t distribution (looks Gaussian).
Desrcribe mixing among the three neutrino generations
Which are atmospheric and solar neutrinos?
Firstly, the neutrinos we think of are the weak (production) eigenstates. These couple to the mass (propagation) eigenstates through a mixing matrix which just specifies a certain rotation. Known as the PMNS matrix. Form orthogonal basis sets, and matrix is Unitary.
In 2d, the mass eigenstates are free-particle solutions. Therefore, v_e can be decomposed into cos(theta)v_1 + sin(theta)v_2.
delta_m31/delta_m32 ~ atmospheric
delta_m21 ~ solar
From oscillations, there are two possible assignments of mass hierarchy. Normal or Inverted
What are the difference Neutrino Sources to study oscillations?
Sun (solar), Cosmic Rays (Atmospheric), Nuclear Reactors (Reactor), Accelerators (Beam).
Using these sources, we can either study Dissappearance (deficit compared with expectations due to oscillations away from flvaour produced into flavours that the experiment cannot detect).
Appearance - of Neutrino flavours that were not present at production.
Give an example of neutrino dissapearance in CC threshold kinematics?
Electron Neutrinos from the sun and from Reactors that oscillate into muon or tau neutrinos cannot interact via charged current interactions. Energy of about 1 MeV so below threshold for CC with nucleons.
Describe the Parameterisation of the PMNS matrix
Composed of 3 rotation angles and a complex phase. theta_12 from solar and reactor neutrino experiments. theta_23 from atmospheric and beam neutrino experiments. theta_13 from Reactor neutrino + future experiments.
DONT yet know phase, will get this from future experiments.
Super-Kamiokande Detector. Desribe what it is?
How does it detect Neutrino oscillations?
50kton of ultra-pure water 1km underground in Kamioka, Japan. Relativistic e and mu produced when neutrinos interact with neutrons in CCWI. Cherenkov rings are produced detected in 11,000 Photomultiplier tubes. Mu scatter less so rings are sharper as oppose ot e.
Neutrinos coming from above detector do not travel enough to oscillate. However those coming from below trave lsignifcant further distance, hence have time oscillate. Measure as a function of the zenith angle (vertical). See dissapearance for muon neutrinos, so must be oscillating into the tau neutrino.
At large distances, around half survive.
How is Neutrino Beam Physics Studied?
Atmospheric, solar neutrinos have wide spread of initial energies. Beam neutrinos do not. Collide high energy protons with a fixed target - mainly produce pions. Focus the positive pions and they will decay to muon, muon neutrino. Focus the beam to collect the neutrinos that are slightly off axis - these have the the narrower energy distribution. Make sure L/E is at a oscillation maximum.
Near detector can measure components at production, while far detector measures dissapearance of muon neutrino.
Depth of minimum - sin^2(theta_23). The position of minimum gives delta_m squared.
