Class #9 (March 28) Reading Questions - Particle Physics, Secs. 30-36

 

 

1. Why does the original Gell-Mann model for quark structure of hadrons seems to require an additional quantum number (known as color) for the quarks.  Is there any direct experimental evidence for this extra quantum number.

 

2.  What is meant by "flavor" SU(3) and "color" SU(3).  How does the hypothesis that all hadrons must be colorless help to "clean up" the SU(3) representation of the hadrons?

 

3. Noether's theorem states that for every symmetry property of the Lagrangian there is a conservation law and visa versa.  Thus, conservation of electric charge and conservation of color charge can be viewed as the origins of QED and QCD, respectively.  What is the difference between electric charge and color charge?  How are photons similar to and different from gluons? 

 

4.  The short-range nature of the weak interaction is attributed to the large masses of the force transmitting W and Z bosons.  Can we use the same argument to explain the short range nature of the strong interaction?

 

5.  Fig. 32.2 shows that as one gets closer to an electron its electric charge increases while as one gets closer to a quark its color charge decreases.  Explain how this distance dependence comes about and how, in the quark case, it gives rise to what is known as asymptotic freedom.

 

6. Figs. 33.2 and 33.3 show the difference between electric field lines and color force lines.  Explain why the color force lines form "flux tubes" and how this results in quark confinement.

 

7. Explain what is shown in Fig 35.2.  In particular, what is R and why does it jump from a value of 2 to a value near 4 in the energy range E = 3-5 GeV?  Also, what are the J/psi and upsilon particles?

 

 

Your Question:  Please give a well-formulated question that you have regarding the material covered in this reading assignment.