Question: Why do the heavy nuclei clump above the red line - PowerPoint Presentation

Slide1

Question: Why do the heavy nuclei clump above the red line ?

Nuclear Physics

Hint: What are the competing interactions ?

Question: Which are β

+ or β- emitters ?

Ans

: Attractive Strong Interaction and repulsive Coulomb interaction. Easier to add neutrons when there is a large Coulomb repulsion.Slide2

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.Slide3

Today’s plan

Return homework and quizzes.

Quiz reviewMore on the weak interaction: CKM matrixWarm 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.Slide4

Quiz 6:Slide5

Question: Why is the J/

ψ

so narrow (factor of 50) ?

Hint if needed.

Ans

: OZI suppression and running of α

SSlide6

Upsilon(4S) can decay to pairs of B-anti B mesons (hence it is quite broad)

Upsilon(1S), Upsilon(2S), Upsilon(3S) can only decay through 3 gluons and hence their widths are strongly suppressed.

Similarly, the J/

ψ

(1S),

ψ

(2S) are narrow while the

ψ

(3S) is above threshold for decay to D

Dbar

and is broad.Slide7

Review:

Recall only 4 interactions possible.Slide8

Ratio of 0.45;

valence quarks are fractionally charged with

some sea contribution

Review:

PDG PlotSlide9

Review: Dimensional arguments for neutrino fixed target

Note G

F

~ 1/E

2 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~L

2Slide10

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 ?Slide11

Note that

V

us

and

V

cd

are singly

Cabibbo

suppressed.Slide12

Big Bang Theory EpisodeSlide13

How to observe top quark decay at the

Tevatron

Question: How is the LHC different ?

Ans: Gluon-Gluon fusion rather than quark-antiquark Slide14

Measurement of V

ubTwo 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 ?Slide15

Inclusive measurement of

V

ub

Look for leptons with momenta beyond the kinematic limit for

bc decaySlide16

https://

arxiv.org/

pdf/hep-ex/0202019.pdf

CLEO collaboration at CESR in Ithaca, NY Slide17

Inclusive measurements of

V_ub

(CKM example)Slide18

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 105.6 MeV

Another hint: How does the width of the

weak

leptonic

decay depend on its mass ? (Use weak interaction and dimensional analysis) Slide19

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 ?Slide20

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 argonSlide21

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: B

0

= bbar

d or anti-B

0

= b

dbarSlide22

Feynman diagram for process 1)

Can you draw the Feynman diagram for process 4) ? (Hint it is

Cabibbo

suppressed).Slide23

Feynman diagrams for process 3)Slide24

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

Slide25

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

. 2

nd

order processes !

Question:

Are these

strong, weak or EM

processes

?

Question: Are the decay process strong, weak or EM ? Why

Ans

: Weak;

strangess

changing.Slide26

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.Slide27

Question: How much do the K

S

and K

L

lifetimes differ ? What is the mass difference in milli-electron volts ?