Quark Velocity

deal4428

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Oct 24, 1999, 3:00:00 AM10/24/99

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I seem to remember reading somewhere that one of the problems in detecting
quarks was that their mean free path was small since they tended to run into
gluons quickly and so lose the free path quickly.
My question is before they interact with gluons do quarks travel at c? And
do they move in the straightest possible path (like photons)?
Thanks

Moataz H. Emam

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Oct 25, 1999, 3:00:00 AM10/25/99

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That is more difficult to answer than may seem. My initial reaction was
to answer yes to both questions. But on second consideration, I realize
that quarks are always in a bound state, like the electrons to the
atoms. And quantum mechanically, particles in bound states do not
"really" move, but exist as energy eigenstates of the system - whatever
that may be. However, working roughly, the answers to your questions are
YES.

--
Moataz H. Emam

URL: http://www-unix.oit.umass.edu/~emam/
The Department of Physics and Astronomy
1129, Lederle Graduate Research Tower C,
University of Massachusetts, Amherst
e-mail : em...@physics.umass.edu
Tel. : (413) 545 0559
============================================

Matthew Nobes

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Oct 25, 1999, 3:00:00 AM10/25/99

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On Sun, 24 Oct 1999, deal4428 wrote:

> I seem to remember reading somewhere that one of the problems in detecting
> quarks was that their mean free path was small since they tended to run into
> gluons quickly and so lose the free path quickly.

Well, I'm not sure that's how I would picture confinement of quarks. The
standard picture is the "flux tube" one. Basically you can think of a
quark and antiquark as connected by a thin tube of "electric" field lines.
(here the "electric" means the color force analogue of the elecrice
field). As the quarks are pulled apart the potential energy between the
two quarks gets larger (as opposed to smaller, as is the case in standard
E&M). When the energy exceeds twice the mass of the quarks a new
quark-antiquark pair is created. (some of this is backed up by lattice
QCD studies).

> My question is before they interact with gluons do quarks travel at c?

No, all of the quarks have mass, therefore they do not travel at c.

> And do they move in the straightest possible path (like photons)?

That is a complicated question. I don't think that classical notions like
paths really apply inside hadrons, for two reasons.

1) The whole thing is quantum mechanical, as the other response to this
post pointed out it is better to think of energy levels

2) The interaction is extremly strong. You have a whole "sea" of virtual
quark-antiquark pairs popping in and out of the vaccuum. This complicates
questions like "which quarks make up the hadron?"

Ian Bannister

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Oct 25, 1999, 3:00:00 AM10/25/99

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In article <el8K1KmH$GA.265@cpmsnbbsa03>, "deal4428"

<deal...@email.msn.com> wrote:
>
> I seem to remember reading somewhere that one of the problems in detecting
> quarks was that their mean free path was small since they tended to run
> into gluons quickly and so lose the free path quickly.

> My question is before they interact with gluons do quarks travel at c? And

> do they move in the straightest possible path (like photons)?

> Thanks

Quarks are generally considered to have a rest mass so cannot move at c.
Their E/c^2 is significant though so the mass of a bound system like a
proton is much greater than the mass of it's constituents.
Trying to create an unbound quark fails because the energy required to
separate them is enough to create a new quark/anti-quark pair.

uud -> uu----d -> uud + dd(bar) -> uud + 2photons
etc.

--
|-*- Ian Bannister