Can particle colliders create Bare Quarks ??

[Widdekind]

Have scientists seen "bare" exotic quarks (s, c, b, t), or do they only appear in Mesons & Baryons ?

[PaulS1950]

As I understand it - and I could be way wrong - free quarks have a limited life because they bond so readily.

[Mr Skeptic]

No one has been able to get a bare quark of any kind. You can get your quarks in quark-antiquark pairs or triplets of either quarks or antiquarks. Recently I've even heard of getting a combination of the above. But I haven't heard of any lone quarks. The reason for this is that the binding energy for the quarks is bigger than the quark mass, so anything that would have enough energy to separate a quark from his buddies would have enough energy to make a quark-antiquark pair instead.

[Severian]

The top quark is always free, because it decays before it can become confined in a hadron.

[Widdekind]

"Quarks never appear in isolation. This process of Hadronization occurs before quarks formed in high-energy collisions can interact in any other way. The only exception is the top quark, which may decay before it Hadronizes" (ISBN 9781155255507, pg. 50).

 

Thanks for all the responses

Edited July 31, 2010 by Widdekind

[Widdekind]

If one can say, that "there are no free quarks"...

 

then, can one say, that "there are no Delocalized quark Wave Functions" ? Does not the Color Force, carried by the "glue", constantly "compress" the Wave Functions, of quarks, "jacking up" their effective mass-energy, from 4-5 MeV, to 100 MeV (Mesons) or 300 MeV (Baryons) ? And, wouldn't this Color Confinement also imply, that the resulting composite-particle Hadron Wave Functions would also be highly localized (~1 fm) ?

 

A qualitatively plausible mechanism is suggested by the 'MIT Bag Model'. Free quarks, of [bare] mass m, confined within a spherical shell [bag "skin"] of radius R, are found to have an effective mass [math]m_{eff} = \sqrt{m^2 +(\hbar x/ R c)^2}[/math], where x is a dimensionless number around 2.5. Using the radius of the proton (say, 1.5 fm) for R, we obtain m_eff = 330 MeV/c² for the up & down quarks. See Close, F.E. (1979) An Introduction to Quarks & Partons, Academic, London, Section 18.1.

 

D. Griffiths. Introduction to Elementary Particles, pg. 151.

[Bob_for_short]

No one has been able to get a bare quark of any kind. You can get your quarks in quark-antiquark pairs or triplets of either quarks or antiquarks. Recently I've even heard of getting a combination of the above. But I haven't heard of any lone quarks. The reason for this is that the binding energy for the quarks is bigger than the quark mass, so anything that would have enough energy to separate a quark from his buddies would have enough energy to make a quark-antiquark pair instead.

Quarks were conceived as bound entities, let us not forget it. So whatever energy is used to "separate" them, they will always come together.

The reason for this is that the binding energy for the quarks is bigger than the quark mass, so anything that would have enough energy to separate a quark from his buddies would have enough energy to make a quark-antiquark pair instead.

It is popular but not correct explanation because it may still imply some probability of creating separated quarks in pairs. In fact, the only "explanation" is the quark definition as charged species in bound states. In other words, gluons are always meant to be inplace. Unfortunately a "gauge" way of introducing quarks and gluons (via "gauge covariant derivative") makes an illusion that quarks may be free, at least theoretically - if we neglect the gluon field.

 

If we introduce quarks as quasi-particles in compound systems, there will be no question about their observing as free particles. This way is quite phenomenological and physical.

 

Very simplified and comprehensible model is given in my "Reformulation instead of Renormalizations" paper (http://arxiv.org/abs/0811.4416).

Edited August 5, 2010 by Bob_for_short

[Widdekind]

It is popular but not correct explanation because it may still imply some probability of creating separated quarks in pairs. In fact, the only "explanation" is the quark definition as charged species in bound states. In other words, gluons are always meant to be inplace.

 

If a quark is bound to other (anti-)quarks, that whole system of particles is completely confined in a "bag", whose "skin" is the "slime" of glue, that "epoxies" them together. In order to extract a quark, you must stretch the "slime skin" of the "bag". Eventually, the "bag" tears, and, where it rips, "in the middle", the gluon's color creates a quark (on one side of the rip), while its anti-color creates an anti-quark (on the other side of the gap).

 

I understand, that there is a "slow stretch mode" (my words), wherein gluons can "spawn" more glue, and gradually lengthen the bond; and, a "fast tear mode" (my words), wherein hard-hit quarks can "rip free" straight away, before the glue "tendons" have time to self-generate more glue (from the input mechanical stretch energy). This is why, at higher & higher energies, quarks look lighter & lighter -- they "rip free" trailing less & less glue.

 

Apparently, it looks like, as you asymptote towards infinite incident energy, free quarks would "rip free & clear", completely, and "bare quarks", of mass-energy equivalent 4-5 MeV would be (briefly) born.

 

Is this an accurate (if not particularly precise) picture ? Could you, in theory, create an "infinitely" long glue "tendril" gluon bond, by "slowly stretching" the bond, sufficiently slowly, for sufficiently long ?

 

Here's another picture, from Hey & Walters' New Quantum Universe (pg. 270):

 

 

Uploaded with

ImageShack.us

[Bob_for_short]

If a quark is bound to other (anti-)quarks, that whole system of particles is completely confined in a "bag", whose "skin" is the "slime" of glue, that "epoxies" them together. In order to extract a quark, you must stretch the "slime skin" of the "bag". Eventually, the "bag" tears, and, where it rips, "in the middle", the gluon's color creates a quark (on one side of the rip), while its anti-color creates an anti-quark (on the other side of the gap).

 

I understand, that there is a "slow stretch mode" (my words), wherein gluons can "spawn" more glue, and gradually lengthen the bond; and, a "fast tear mode" (my words), wherein hard-hit quarks can "rip free" straight away, before the glue "tendons" have time to self-generate more glue (from the input mechanical stretch energy). This is why, at higher & higher energies, quarks look lighter & lighter -- they "rip free" trailing less & less glue.

 

Apparently, it looks like, as you asymptote towards infinite incident energy, free quarks would "rip free & clear", completely, and "bare quarks", of mass-energy equivalent 4-5 MeV would be (briefly) born.

 

Is this an accurate (if not particularly precise) picture ? Could you, in theory, create an "infinitely" long glue "tendril" gluon bond, by "slowly stretching" the bond, sufficiently slowly, for sufficiently long ?...

 

Let us consider two bodies connected with a spring. It is a mechanical system and is described with mechanical equations. I analyzed it (with another purpose though) and I see that according to the mechanical equations for, say, particle 1, it feels the force (attractive or repulsive depending on phase of oscillations) from the second particle. So if you hit the first particle quickly, its back reaction (effective mass) will essentially depend on the phase of oscillation. In other words, the spring (the glue) may "help" the external force push particle 1 or may "resist". We must keep this peculiarity in mind while analyzing the scattering data. The picture with static quarks and gluons is not realistic - they oscillate.

Edited August 26, 2010 by Bob_for_short