1. Nuclear Physics
Question: Why do the heavy nuclei clump above the red line ?
Hint: What are the competing interactions ?
Ans: Attractive Strong Interaction and repulsive Coulomb interaction. Easier to add neutrons when there is a large Coulomb repulsion.
Question: Which are β+ or β- emitters ?

2. Question : Which of the following has the most stable isotopes:
N odd, Z odd
2) N odd, Z even
3) N even, Z even
4) N even, Z odd
Remember the shell model and Pauli exclusion principle.

3. Today’s plan Chapter 8 on oscillations
Return homework and quizzes.
Quiz review
More on the weak interaction: CKM matrix
Warm up material on mixing (Chapter 8).
Quiz on Weak Interactions
(Friday April 14th)
Chapter 8 on oscillations
and mixing of mesons on Wednesday.
“Warm up” material today.

4. Quiz 6:

5. Question: Why is the J/ψ so narrow (factor of 50) ?
Hint if needed.
Ans: OZI suppression and running of αS

6. Upsilon(1S), Upsilon(2S), Upsilon(3S) can only decay through 3 gluons and hence their widths are strongly suppressed.
Upsilon(4S) can decay to pairs of B-anti B mesons (hence it is quite broad)
Similarly, the J/ψ(1S), ψ(2S) are narrow while the ψ(3S) is above threshold for decay to D Dbar and is broad.

7. Review:
Recall only 4 interactions possible.

8. Review:
PDG Plot
Ratio of 0.45; valence quarks are fractionally charged with some sea contribution

9. Review: Dimensional arguments for neutrino fixed target
Note GF ~ 1/E2 and s ~E2 . Now calculate s in the fixed target neutrino nucleon scattering.
Another example, e+e- hadrons or e+e- μ+ μ-
Here alpha is dimensionless and sigma~L2

10. Review question: Draw the dominant Feynman diagrams for the decay of the top quark ?
Hint: There are two classes of final states: those with quarks and those with leptons
Hint: Does t ->s or t->d ?

11. Note that Vus and Vcd are singly Cabibbo suppressed.

12. Big Bang Theory Episode
Whiteboard by David Saltzberg

13. How to observe top quark decay at the Tevatron
Question: How is the LHC different ?
Ans: Gluon-Gluon fusion rather than quark-antiquark

14. Measurement of Vub
Two methods: use an exclusive bu decay mode or inclusive bu
Question: Can you draw the Feynman diagram for this decay mode (show the couplings)
Question: What would be an “inclusive” bu decay ?

15. Inclusive measurement of Vub
Look for leptons with momenta beyond the kinematic limit for bc decay

16.
CLEO collaboration at CESR in Ithaca, NY

17. Inclusive measurements of V_ub (CKM example)

18. Weak Interaction Review Problem
The former has a branching fraction of 100% and the latter is 16%. The muon lifetime is 2.2 microseconds. Calculate the tau lifetime.
Hint: the tau mass is 1776 MeV and the muon mass is MeV
Another hint: How does the width of the weak leptonic decay depend on its mass ? (Use weak interaction and dimensional analysis)

19. Weak Interaction Review Problem
The former has a branching fraction of 100% and the latter is 16%. The muon lifetime is 2.2 microseconds. Calculate the tau lifetime.
How do we get the tau lifetime from the width ?

20. Weak Interaction Review Question
Muons have the same electromagnetic charge and weak interactions as electrons and yet a muon with an energy of a few GeV passes through an iron slab while an electron of the same energy does not. Explain why.
Ans: Electrons bremsstrahlung and produce electromagnetic showers
2.5 GeV electron in liquid argon

21. Weak Interaction Review question:
Find the valence quark composition, dependence on CKM matrix elements and relative rates of the following processes (order them by strength).
Hint: B0 = bbar d or anti-B0= b dbar

22. Feynman diagram for process 1)
Can you draw the Feynman diagram for process 4) ? (Hint it is Cabibbo suppressed).

23. Feynman diagrams for process 3)

24. Find the valence quark composition, dependence on CKM matrix elements and relative rates of the following processes.

25. Warm-up for Chapter 8 (neutral mesons’ oscillation and CP violation)
Neutral mesons such as the K0 or B0 may transform into their anti-particles (anti-K0, anti-B0) and vice versa.
Question: Which interaction is responsible for this phenomena called “mixing” ? Why
Ans: Weak interaction, these are ΔS= 2 or ΔB=2 transitions. 2nd order processes !
Question: Are these strong, weak or EM processes ?
Ans: Weak; strangess changing.
Question: Are the decay process strong, weak or EM ? Why

26. Neutral kaon are produced by the strong interaction but decay by the weak interaction.
This is described by simple time-dependent quantum mechanics.
The strong interaction eigenstates differ from the weak interaction eigenstates. They are linear combinations.

27. Question: How much do the KS and KL lifetimes differ
Question: How much do the KS and KL lifetimes differ ? What is the mass difference in milli-electron volts ?