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Quark Theory
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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Update: June 2012
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