Where are the Quarks ?

[Widdekind]

According to Fundamentals in nuclear physics: from nuclear structure to cosmology, by Jean-Louis Basdevant, James Rich, Michel Spiro (pg. 156), the Electric Charge distributions, of nucleons, are essentially spherically symmetric:

 

Uploaded with

ImageShack.us

 

Where is the evidence of 3 quarks, in the aforegoing figures ?

[elas]

Just as a graph of Earth's gravity field cannot be used to deduce the presence of individual atoms so the graphs you quote cannot be used to discern the internal structure of proton and neutron; take a look at the chapter on quarks in The Particle Explosion by Frank Close, Michael Marten, and Christine Sutton.

[swansont]

Are those graphs being presented as evidence of three quarks?

[Widdekind]

Not to my knowledge, which was why I'm confused. Frank Close's The New Cosmic Onion explicitly states that the charge of the proton is concentrated inside 3 distinct quarks, embedded in "electrically neutral material", thought to be the gluon field "glue".

---

Merged post follows:

Consecutive posts merged

In D.Griffiths' Intro. to Elementary Particles (2nd ed.), quark Wave Functions are often modeled using standard, electronic, Hydrogen Atom Wave Functions -- the same also "recycled" for modeling Positronium.

 

Thus, maybe quarks are "small" (10^-18 m) in the same sense as electrons are always said to be "small" (10^-18 m) (as seen here), even tho their WFs are much larger (10^-18 m for quarks, 10^-10 m for electrons).

[swansont]

Not to my knowledge, which was why I'm confused. Frank Close's The New Cosmic Onion explicitly states that the charge of the proton is concentrated inside 3 distinct quarks, embedded in "electrically neutral material", thought to be the gluon field "glue".

 

We have distinct charges in atoms, yet they are electrically neutral as a whole and can have various values of magnetic moment. So I'm not seeing the connection. The charge distribution in neutrons and protons is not offered as evidence of quarks. The evidence of quarks lies elsewhere.

[Widdekind]

From analyzing the aforecited figure, it looks like, compared to those of up quarks, the Wave Functions, of down quarks, are more "squeezed", into intermediate radii. To wit, the positive charge distributions of up quarks dominate, even relative to their greater electrical charges, in the inner core, and outer limbs, of the nucleons.

 

Uploaded with

ImageShack.us

[Widdekind]

"Best of Both Worlds" Resolution (???) -- Unperturbed Quark Wave Functions are extended [~10^-15m], but collapse into quasi-structureless points [< 10^-18m] upon Perturbation

 

(1) Quark Wave Functions collapse upon perturbation by impinging Electrons / Neutrinos

 

According to Robert Lanza's Biocentrism:

No small object actually assumes a particular place, or motion, until its Wave Function collapses. What accomplishes this collapse? Messing with it in any way. Hitting it with a bit of light, in order to "take its picture", would instantly do the job.

(pp. 50-51)

 

 

(2) Immediately after perturbation impact, Nucleons are comprised of 3 point-like [Valence] Quarks in a "sea" of Gluons & Quark/Antiquark pairs [produced upon Gluon bonds breaking]

 

According to F.E.Close's An Introduction to Quarks & Partons:

pion production begins at Q² = 0.1 GeV²

gluon & quark-antiquark sea production begins at Q² = 5 GeV²

valence quark contributions [to nucleon momentum] are [swamped by continuum [sea] excitations at Q² = 100 GeV²

(pg. 195)

 

u & d [valence] quarks dominate nucleon momentum at the lowest energy collisions

quarks emit gluons at higher energy transfers

more gluons & quark-antiquark pairs are produced at still higher energies

at the highest energies (~100 GeV), an equilibrium is reached where the nucleon momentum shared amongst all types of quarks & gluons equally

(pg. 196-7)

 

exotic (s,c) quarks are always produced in the sea [by gluon bond breaking (?)]

below the charm quark production threshold, roughly half of the nucleon's momentum is carried by gluons

 

More specifically, the nucleon's momentum budget breaks down as:

5%

antiquarks

*

(all in the sea)

45%

quarks

50%

gluons

[electrically neutral material unaffected by

Eletro-Weak

interactions]

(pg. 231-34; 242-43, 256)

* Antiquarks are only produced in quark/anti-quark pairs. Therefore, these figures seemingly suggest, that 10% of the nucleon's momentum comes from broken gluon bonds (quark/antiquark pairs), 50% from gluons, and 40% from the three (3) main Valence [or "structural"] quarks. So, glue mass dominates sea quarks, even as it may dominate the masses of valence quarks (m₀ = 4-5 MeV, m_eff = 330 MeV)

 

The sea is an SU(N) singlet [spin zero, Quantum Entangled (?)] state

(pg. 247)

 

 

 

 

 

Edited July 24, 2010 by Widdekind

[Widdekind]

Asymptotic Freedom -- Quarks are like Tether-Balls, "feeling free off the fist", but bound back to the pole after a few feet (???)

 

According to the Bag Model, inside Hadrons, quarks are kept confined by a bag-like "skin" of "sticky slime". That "glue" is concentrated at the surface "skin" of the Hadron (r ~ 10^-15m). When high-energy Leptons are beamed at, and into, Hadrons, they stream through that "sticky slime skin", probably (???) w/o interacting with those gluons, since Leptons are "color blind", and do not interact via the Strong (Color) Force. Once inside the Hadron, the Leptons interact with the constituent 'structural' quarks, causing their Wave Functions to collapse, or localize, into little (apparently) point-particles (r < 10^-18m). At first, before those collapsed constituent quarks can careen out into the "sticky slime skin" of the gluon field, they scatter the incident Leptons like free particles.

 

Now, at low Lepton energies, when gluon bonds begin to break, perhaps (???) a little like taughtened taffy thinning in the middle, those gluons can beget more gluons, to help hold together the tendon-like bond. In this "slow stretch" mode, the Lepton's incident energy can be absorbed into the "glue", perhaps (???) a little like kevlar bringing a bullet to a soft stop. But, at high Lepton energies, quarks are thrust through the "sticky slime" far too fast for that "re-forming effect", of the gluons' broken bonds, to take place. Thus, the threads of "sticky slime" simply "snap", before any incident Kinetic Energy can be absorbed into those bonds -- perhaps (???) a little like a swiftly speeding sniper bullet penetrating a kevlar coat. Thereby, harder & harder hit quarks act as if they are "entrained" with less & less glue, and so look like lighter & lighter (point) particles.

 

To resolve the interior structures of nucleons (r ~ 10^-15m), Leptons must have high energy (l < 10^-15m, E > 1 GeV). Thus, nucleons (m c² ~ 1 GeV) can disintegrate under such circumstances, shattering into a "scree spray" of naked quarks, antiquarks, & gluons, each carrying only a tiny fraction of the original nucleon's momentum. However, such collisions are often quasi-elastic, so that the incident Lepton only transfers a tiny fraction, of its incident energy, into the nucleon. In some sense, the Lepton's Wave Function, then, "flows through", and only "ruffles", the nucleonic Wave Functions, of the three structural quark cores, and all of their entrained gluons.

 

 

 

 

 

 

References:

 

G. Aubrecht. Quarks, Quasars, & Quandries, pp. 68-72.

 

We talked about electron-positron annihilation, into Hadrons, proceeding through the formation of a quark-antiquark pair. The quarks materialize into Hadrons... which remember the direction of their parent quarks [Conservation of Momentum ???]. That gives us two-jet events.

 

In much the same way, now that we have invented gluons interacting w/ the quarks, we may imagine that sometimes one of the outgoing quarks radiates a gluon:

 

electron-positron --> quark + antiquark --> (quark + gluon) + antiquark

...When that happens, I expect my two-jet event to change into a three-jet event. One quark jet splits into a quark jet and a gluon jet.

 

At high energies, in electron-positron annihilations, three-jet events are quite common... [Often] you can see one fully developed jet, and two smaller jets. The fully developed jet may represent debris from the quark. Then, the smaller jets are the offspring of the antiquark & gluon. The frequency at which these events are seen, and the detected properties of the events, are all consistent with the idea that the mechanism for generating them really is a quark, an antiquark, and a gluon, in the semifinal state before the Hadrons materialize [Hadronization].

 

Now I want to talk about [vacuum] polarization effects, & the effective [colour] charge of the quarks. There will be similar screening effects to the one we discussed for [quantum] electrodynamics... Just as before, if I ask, "at a certain radius, how much redness lies w/in a circle [sphere]?", the result will be less than the redness of the test [colour] charge, b/c some of it is screened out, or canceled... There is color charge screening in this case, which tells you that the effective [colour] charge tends to become larger, as you probe on shorter distance scales. This is entirely analogous to what we saw in QED.

 

The difference, in this case, is that there is something else that can happen, b/c gluons carry color [charge]. B/c the gluons carry color [charge], quarks can Camouflage themselves, and hide their color... [imagine a] red quark. We now send some emissary in, to say, "hello, are you red?" While our emissary is on the way in to ask whether this is a red quark, the quark can fluctuate, quantum mechanically, into a quark and a gluon. And, if it chooses to, it can fluctuate into a green quark, and a red-antigreen gluon. The red-antigreen gluon goes out, and takes a walk, in quantum mechanics space...

 

Our probe arrives, and says, "hello, are you red?" And the quark says, "no, I'm green, go away." So, b/c of the fluctuations made possible by the fact that gluons can carry color, you find, if you look too closely, less red charge than you thought was there. In order to see the full red charge, you've got to look on a bigger scale, the scale of the promenade of the gluons.

 

We have two effects going on: one, the normal screening effect as in [quantum] electrodynamics; the second, the Camouflage effect, made possible b/c, unlike photons, which don't have an electric charge, the gluons do have a color charge.

 

There's a competition, between these two effects, and in the theory we believe to be true, QCD, Camouflage wins. The consequence of this, is that the Strong [Colour] Force, as measured by the effective color charge, becomes weaker and weaker at short distances. If you look closer and closer, you find that the strong [colour] charge is getting tinier and tinier. What this means, is that, for practical purposes, if you find quarks close together, in a small space inside a bubble or a little balloon or bag, they behave almost as independent particles. B/c of this Camouflage effect, as long as the quarks remain close together, each one hardly feels the color charge of the others.

 

On the other hand, if you try to separate two quarks by a large distance, then each is able to see more clearly the full charge of the neighboring (but no longer very close) quark. And, so, the Strong [Colour] Force becomes more formidable, as you go to large distances. We believe that this effect, properly implemented, is responsible for the fact, that we can talk about the quarks as being quasi-free particles w/in protons, but we can't extract the quarks from the protons. The net antiscreening of color charge gives us the possibility of understanding that apparent paradox.

 

Fig. 3 --

Apparent relation, of

Gluon

density, to gradient of

Quark

density, seemingly suggests

(???)

some sort of "self-consistent" solution, and/or that

Quark

momentum is associated w/

Gluon

emission. This picture apparently purports, that

Nucleons

are a little like "

glue

bubbles". The "sticky slime" slathers the surfaces of

quarks

, "constricting" them radially inwards, with powerful implosive pressure.

 

 

Fig. 5 --

By

Camouflage

,

quarks

expel their

color charge

, thereby "blanching" and becoming

color neutral

(

White

). In crude conception,

quarks

"blanch" by "oozing" a shrouding "

Camouflaging

cocoon" cladding of "sticky slime"

glue

, composed of a

gluon triplet

. Each

gluon

in the

triplet

carries, quantum mechanically, 1/3

^rd

of the emanating

quark

's color charge

, combined with 1 of the 3

anticolors

. Thus, each

gluon triplet

, in sum, carries 1

color

, whilst being

anticolor antineutral

(

Black

). Then, each "blanched"

color neutral

quark

(

White

) attracts the "blackened"

anticolor antineutral

gluon triplet

(

Black

) that it emanated

(

White <---> Black

)

. Meanwhile, those 3

gluon triplets

, each carrying, quantum mechanically, the

monochromatic color charge

, of their parent

quarks

, are themselves mutually attracted & bound, by the

Strong (Color) Force

, thereby becoming, in combination,

color neutral

(

White

). Thus, in

Lepto-production

collisions, the incident

Leptons

interact

Electromagnetically

with the

Camouflaged

constituent quark cores

, which interact

Chromodynamically

with their own

Camouflaging

"cocoon cladding" of

colored

glue

, which "sticky slime shrouding shells" mutually interact, again

Chromodynamically

:

 

Lepton

<---EM--->

quarks

<---CD--->

own

gluons

<---CD--->

others'

gluons

This "loose linkage" may act as a kind of "shock absorber", complicating the dynamics of

Lepto-production

collisional interactions.

 

 

 

 

 

 

Andrew Watson. The Quantum Quark, pp. 285-287.

 

How to reconcile these quark model masses, w/ the other set of oft-quoted quark mass values? In Chapter 4, the up & down quarks were ascribed masses of 4 MeV & 7 MeV, respectively, very different from the 300 MeV or so for the constituent quark masses. These smaller values, extracted from pion-decay data, are termed current quark masses... A constituent quark is a current quark surrounded by a gluon cloud, and it's this cloud that carries most of the mass, and which gives rise to the difference between the two sets of mass values...

 

The quark mass depends on energy. In this way, quark masses are not fixed, but are "running" masses that decrease as the energy is increased... For three-jet production, in electron-positron collisions, Marti i Garcia and his colleagues deduced a value of 2.67 +/- 0.50 GeV for the b quark mass. Their figure, extracted at an energy of 91 GeV, the mass of the Z boson, is just 60% of the quoted value of the b quark mass [4.5 GeV] at 1/20 of the energy [4.5 GeV], based on studies of the Upsilon meson [Bottomonium in excited Spin state (S=1)]. This fall in b quark mass with increasing energy is in line with the running mass prediction of QCD.

 

 

Books LLC. Quarks: Quark, Strange Quark, Top Quark, Isospin, Down Quark, Up Quark, Bottom Quark, Hypercharge, Charm Quark, Baryon Number.

 

Part of the effects of virtual quarks & virtual gluons, in the 'sea', can be assigned to one quark so well, that the term 'constituent' quark ['structural quark'] seems appropriate. According to the Feynman Diagrams, constituent quarks seem to be 'dressed' current quarks, i.e., current quarks surrounded by a cloud of virtual quarks & gluons. This [gluon] cloud, in the end, explains the large [effective] constituent quark masses. The effective quark mass is called the constituent quark mass. Hadrons consist of "glued [together]" constituent quarks.

(pp. 17-18)

 

Current quarks (also called naked quarks) are defined as the constituent quark cores (constituent quarks with no covering [of glue]) of a valence quark. If, in one constituent quark, the current quark is hit inside the covering with large force [high energy], it accelerates through the covering, and leaves it behind. In addition, current quarks possess asymptotic freedom (w/in the perturbation theory described limits). The mass of the current quarks carries the designation current quark mass.

(pg. 19)

 

The current quark mass is also called the mass of the 'naked' quarks. The mass of the current quark is reduced by the term of the constituent quark covering mass... The current quark masses, of the light current quarks, are much smaller than the constituent quark masses. [The] reason for this is the missing of the mass of the constituent quark covering [associated "glue"]...

 

Definition: The current quark mass [~5 MeV] means the mass of the constituent quark [~300 MeV], reduced by the mass of the respective constituent quark covering [adhering "glue"].

(pp. 20-21)

 

Two terms are used in referring to a quark's mass: current quark mass refers to the mass of a quark by itself ["naked" quark], while constituent quark mass refers to the current quark mass plus the gluon particle field surrounding the quark ["dressed" quark]. These masses typically have very different values. Most of a Hadron's mass comes from the gluons that bind the constituent quarks together, rather than from the quarks themselves. While gluons are inherently massless, they possess energy -- more specifically, Quantum Chromodynamics Binding Energy (QCBE) -- and it is this that contributes so greatly to the overall mass of the Hadron. For example, a proton has a mass of approximately 938 MeV/c², of which the rest of masses of its three valence quarks only contribute about 11 MeV/c²; much of the remainder can be attributed to the gluons' QCBE.

(pg. 49)

 

Since gluons carry color charge, they themselves are able to emit & absorb other gluons. This causes asymptotic freedom: as quarks come closer to each other, the Chromodynamic Binding Force between them weakens. Conversely, as the distance between quarks increases, the binding force strengthens. The color field becomes stressed, much as an elastic band is stressed when stretched, and more gluons of the appropriate color are spontaneously created to strengthen the field ["slow stretch" mode]. Above a certain energy threshold, pairs of quarks & antiquarks are created ["fast stretch" tearing mode]. These pairs bind with the quarks being separated, causing new Hadrons to form. This phenomenon is known as color confinement: quarks never appear in isolation. This process of Hadronization occurs before quarks formed in high-energy collisions are able to interact in any other way. The only exception is the top quark, which may decay before it Hadronizes.

(pg. 50)

Edited July 28, 2010 by Widdekind