Day 8.7 Taming the Particle Zoo (13.5)
We have come a long way from Dalton and the indivisible atom. First Thomson finds the electron, Rutherford finds the proton and Chadwick finds the neutron. Then over the next 30 years the list expands to include over 90 different particles. Particle physics of the 50s and 60s is much like chemistry of the 1880s, there is a tremendous amount of data but no theory to provide an organizing structure.
1. Take a deck of particle cards and inspect the information on the cards. They provide the name, mass, spin , charge, Strangeness and the date of discovery. You need to sort the information into three distinct piles. To do this you should use
A) mass B) spin C) charge D) Strangeness
Explain :
2. Start with the spin = 3/2 pile. Use highlighters to colour-code the non-spin information (ie. all Q=0 are pink). Arrange the cards in a table where the rows match one variable and the columns match another. There appears to be a particle missing. Predict its characteristics and write them on the blank card.
3. Repeat with the spin = ½ pile and then the spin =0 pile. There seems to be a particle missing from each of these piles. Predict their characteristics.
4. How is this activity similar to what Mendeleev did with the periodic table?
5. The periodic table puts each element in a specific place. Why does the periodic table suggest that atoms are made of smaller pieces? What do the three tables that you have built suggest about these particles - which include the proton and neutron?

Murray Gell-Mann won the Nobel Prize in 1969 for his theory that explained all of the known particles and predicted more (just like you did in this activity). His original theory proposed the existence of three smaller, more fundamental particles called quarks and their antiparticles.
Quarks have certain characteristics such as charge, spin, and strangeness and they following a set of simple rules:

Quarks have fractional charge and combine to produce integer charge. The up quark has a charge of +2/3 and the strange and down quarks are -1/3. The charges of the antiquarks are the opposite of the quarks.

Strangeness is another property, like charge, and it is conserved in an interaction. The strange quark has a strangeness of -1 and anti-strange is =1.The up and down are zero.

Quarks have spin 1/2. This can be aligned opposite to cancel or in the same way, to add.
6. Mesons are made of one quark and one antiquark. The spins are opposite for a total spin of
0. List all the combinations and calculate their Q and S values. Use the Q and S values to match each meson with its quark-antiquark pair. qq u u ud us du dd ds su sd
Q
S
Spin 0
Mesons
What problems do you see in your results? How could you resolve them? ss
7. Baryons are made of three quarks and can be arranged with a spin of 3/2 or partially cancelled with a spin of ½. List all the combinations of quarks and calculate their Q and S values. Use the Q and S values to determine the quark content for each meson. qqq
Q
S
Spin 3/2
Baryons
Spin 1/2
Baryons ddd udd uud uuu dds uds uus dss
What problems do you see in your results? How could you resolve them? uss sss p. 709 #4, 5, p. 712 #1, 2, 9, p. 736 #21, p. 744 #51