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Name: Unknown
Status: N/A
Age: N/A
Location: N/A
Country: N/A
Date: Around 1993


Question:
I would appreciate someone updating the situation with the quark theory. I ran across an article, I think it was in People magazine, maybe Time, about how researchers were close to finding the last of the quarks that make up the atomic nucleus. Does this mean that the quark model will soon be complete? What about the make-up of the various other sub-atomic particles, have all those quarks been found? As an aside to this, I would also greatly appreciate an explanation of the method that is used to detect quarks, I had heard that they could not exists outside the particles they made up. Also, I know what a 'bubble chamber' is used for but what physically is it and how exactly does it work? One additional thought, what are your opinions on some of the other quantum theories esp. the 'bootstrap' theory? And do you absolutely believe the quark model?



Replies:
Essentially, if you assume that quarks make up the baryons (3) and mesons (2) and that the quarks are conserved, i.e., they can only be made in quark and anti-quark pairs, you can make sense of the kind of products that come about from high energy particle reactions. If you look at the energy that goes into a collision and comes out, along with the momentum you can often, for certain reactions, determine the missing mass of particles that would have participated in the collision, but could not escape the interior of the particles except for short times and distances. These indirect calculations based on the observations of the particles that came out are the way in which we measure and "observe" quarks. Fermilab is rumored to have enough data to give the mass of the last heaviest quark in the standard model. This will give us a final piece of data. However, we do not really know how to calculate the masses of the particles themselves. Our best theory uses a large number of parameters. You will have to read to get a more complete picture.

Sam Bowen


Well, first of all, this last quark (the top quark) really does not appear in the atomic nucleus, except maybe very rarely in the "virtual" sense. The quarks that are supposed to make up the proton and the neutron are the "up" and "down" quarks, which have been known for a long time (the existence of the proton and neutron would be considered evidence for their existence, for example). There is considerable evidence that quarks do exist, or at least that the neutron and proton have internal structure consistent with the quark model. A Nobel prize was awarded two or three years ago for studies of electrons bombarding protons at quite high energies to try to discern this internal structure - there is a Scientific American article by the people who won this prize, published sometime within the last two years.

Arthur Smith



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