Why Isn't a "Gluon Beam" Possible?
Radium
If a *photon* beam [Maser for Microwave, Laser for light] can be made,
then why can't a *gluon* beam be made? The *Gluon* is to the STRONG
force what the *Photon* is to the ELECTROMAGNETIC force. Right?
Thanks,
Radium
Igor Khavkine
There are several obstructions. Due to quark confinement, ordinary
matter is highly color neutral. This means it would be hard to build
the components that a laser needs (cavity, medium, pump, etc.) Also due
to quark confinement, it is very unlikely to see free gluons at all.
Lastly, since QCD is non-Abelian, the gluon field interacts with
itself. In other words, we cannot rely on the ground state of a large
collection of gluons to be the same as the ground state of a large
collection of photons (i.e. all of them bunching up in the lowest
energy state). The last property is essential for the construction of a
laser.
In short, it'd be really tough. Hope this helps.
Igor
Jay R. Yablon
news:1134619994....@z14g2000cwz.googlegroups.com...
The photon is massless and therefore has unlimited range. That is, to
speak classically, the "Coulomb force" spreads out precisely according
to an inverse square law, and there is not any "decay" along the way.
The gluon acts over a very short range, which is why the strong
interaction is short range and so does seem to have a "decay" factor,
classically speaking. So a gluon "beam" with any range we can
experience on a finite scale would seem to not be possible.
This meets up with a very important, and not-yet-answered question,
which is why the gluons, although massless, still have a short range.
The fact that the gluons also carry a color charge (i.e., that strong
interactions are non-Abelian) and so gum each other up in so-called
glueballs, is probably part of the answer, but we do not yet have a
complete answer. This problem sometime goes under the name of the "mass
gap" problem, and it is thought to relate to three interrelated and very
fundamental questions:
1) the short range of the strong nuclear force;
2) the confinement of quarks (especially important); and
3) how and why chiral symmetry is broken.
Solve this problem, and you'll win $1,000,000 from the Clay Mathematics
Institute, and probably pick up a prize in Stockholm as well.
Jay.
_____________________________
Jay R. Yablon
910 Northumberland Drive
Schenectady, New York 12309-2814
Phone / Fax: 518-377-6737
Email: jya...@nycap.rr.com
frisbie...@yahoo.com
I know almost nothing about the strong force, so please allow me to ask
some stupid questions.
So a "free gluon" seems highly unlikely. So now I'm caught in a
dilemma: if the gluons are never free, then how do they get from one
particle to the other, which they must do in order order to exert a
force.
My guess as to the answer: gluons don't really exist, they are a
convenient fiction for calculation of the gluon field. Like photons,
gluons are never really observed. They could be considered an artifact
of the interaction of matter and the strong force.
Another dumb question: are gluons colored?
John Schutkeker
news:1134988916.6...@o13g2000cwo.googlegroups.com:
Not a dumb question, and I think it is the answer to the reason why
gluon beams aren't observed. Since it contains two quarks, gluons *are*
colored, and thus can't be observed directly, because they aren't
"white." However, it would be expected that *some* gluons would be
white, because they would contain a quark and an anti-quark of the same
color.
The reason those can't be observed would then be because existing
accelerators can't produce high enough energies to create them. And if
they could, they would be so short lived that producing a "beam" would
be unrealistic. That's because Heisenberg's uncertainty principle says
that E & T scale inversely with each other. As one increases, the other
must decrease.
AFAIK, the closest possible thing to a gluon beam would be a meson beam.
Those might be roughly similar to q/q_bar pairs I mentioned of the same
color. AFAIK, a meson is a q/q_bar pair, held together by a gluon
field. AFAIK, all mesons have finite lifetimes.
Ulf Torkelsson
> frisbie...@yahoo.com wrote in
> news:1134988916.6...@o13g2000cwo.googlegroups.com:
>
[text snipped]
>>I know almost nothing about the strong force, so please allow me to
>>ask some stupid questions.
>>
>>So a "free gluon" seems highly unlikely. So now I'm caught in a
>>dilemma: if the gluons are never free, then how do they get from one
>>particle to the other, which they must do in order order to exert a
>>force.
Gluons are binding together the quarks inside an elementary particle,
either a baryon like the proton or a meson. A proton consists of
three quarks with different colours, which we can call red, blue and
yellow. The combination of these three colours lead to that the
baryon itself is colourless. The meson on the other hand consists of
a quark with some colour and an antiquark with the corresponding
anticolour, so also the meson is colourless. Each gluon carries one
colour and one anticolour, so they are not colourless. For that reason
they are confined to stay inside the elementary particle that they
belong to, but the quarks in that particle can still exchange gluons,
which is the way in which they change colour. For instance a blue
quark can change to yellow, by emitting a gluon which is blue and
antiyellow, and this gluon can then be absorbed by another yellow quark
which then turns blue, and that way the elementary particle stays
colourless. It is these gluon exchanges that bind the quarks together,
and which is the core of the strong force. A little bit of these forces
will then leak out of the individual particles and bind the protons and
the neutrons in the atomic nuclei together. This is equivalent to how
some of the electromagnetic forces that binds the atoms together in
molecules leak out from the molecules and form the van der Waal's forces
between the molecules.
>>
>>My guess as to the answer: gluons don't really exist, they are a
>>convenient fiction for calculation of the gluon field.
What exists, and what is a convenient fiction is mostly a
philosophical question. You can argue that the gluons are simply
a way to talk about QCD calculations without using mathematics,
and you can say that photons serve the same purpose when we discuss
QED, however.
>> Like photons,
>>gluons are never really observed.
A dark-adapted eye can actually detect an individual photon.
>>They could be considered an
>>artifact of the interaction of matter and the strong force.
>>
>>Another dumb question: are gluons colored?
Yes, each gluon has one colour and one anti-colour.
>
>
> Not a dumb question, and I think it is the answer to the reason why
> gluon beams aren't observed. Since it contains two quarks, gluons *are*
> colored, and thus can't be observed directly, because they aren't
> "white." However, it would be expected that *some* gluons would be
> white, because they would contain a quark and an anti-quark of the same
> color.
No, gluons do not consist of quarks.
>
> The reason those can't be observed would then be because existing
> accelerators can't produce high enough energies to create them. And if
> they could, they would be so short lived that producing a "beam" would
> be unrealistic. That's because Heisenberg's uncertainty principle says
> that E & T scale inversely with each other. As one increases, the other
> must decrease.
You can apply the Heisenberg uncertainty principle to virtual
particles, but particle accelerators produce real particles, thus it
does not say anything about the reason that we do not see free gluons
in accelerator experiments.
>
> AFAIK, the closest possible thing to a gluon beam would be a meson beam.
> Those might be roughly similar to q/q_bar pairs I mentioned of the same
> color. AFAIK, a meson is a q/q_bar pair, held together by a gluon
> field. AFAIK, all mesons have finite lifetimes.
>
Yes, all mesons have finite lifetimes.
Ulf Torkelsson