Class #4 (Jan. 31) Reading Questions - Particle Physics, Secs. 9-10, Handout pgs. 37-47



1. Resonance particles are so short-lived that they can never be directly observed.  How then is one able to determine both the lifetime and mass of such particles?


2.  The baryon and meson multiplets shown in both the text and the handout organize the particles using different axes.  Explain how these different sets of axes related.


3. The octet mass relations found by Gell-Mann (given on pg 68) do not suggest a clear picture of the underlying structure of these sets of particles.  A much more straightforward mass relationship is found for the baryon decuplet: m(delta)-m(sigma*) = m(sigma*)-m(xi*), i.e., there appears to be an equal mass spacing between rows.  Gell-Mann used this to predict the mass of the omega-minus before this particle was discovered.  Using the particle tables included at the end of the handout, repeat Gell-Mann's calculation of the omega-minus mass and compare with the experimental result.


4. Are the sigma-plus and sigma-minus baryons antiparticles of each other?  How about the K-plus and K-minus mesons?


5. The proton and the delta-plus are built from the same quarks.  Are they the same particle?  Please explain.


6. According to the quark model, can we have a baryon with S=0 and Q=-2?  Can we have a baryon with S=1 and Q=-2?  Can we have a meson with Q=-2?


7. Why were people so skeptical about the reality of the quark model for over a decade after the idea was introduced?



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