What is the physical appearance of a proton?

[stonehaven]

Electrons are not really stationary in an atom, the revolve around the neucleus (protons and neutrons). Heres a question that I would like to ask.

We theorize the structure of atome pretty good, as in, the protons and neutrons bunched togeather in the center with the electrons revolving around. But do we have any ideas on what a proton particle looks like? List any links if you know any, thannks.

 

[Astronuc]

Electrons are not really stationary in an atom, the revolve around the neucleus (protons and neutrons). Heres a question that I would like to ask.

We theorize the structure of atome pretty good, as in, the protons and neutrons bunched togeather in the center with the electrons revolving around. But do we have any ideas on what a proton particle looks like? List any links if you know any, thannks.

Protons and neutrons are believed to be composite systems of three quarks. http://hyperphysics.phy-astr.gsu.edu/hbase/particles/proton.html

Structure Evidence from Deep Inelastic Scattering
http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/scatele.html#c1

It is essentially meaningless to ask "what a proton or neutron looks like", since what something looks like is simply a consequence of what the eye perceives from photons scattering from atoms. At the subatomic level, the boundaries are not necessarily as definite as our eyes perceive in the 'observable' reference frame.

 

[Hurkyl]

Electrons are not really stationary in an atom, the revolve around the neucleus (protons and neutrons).

I wanted to object to this. The electron doesn't look like a point particle revolving around the nucleous: it's smeared out across its entire orbital! It really is stationary in the sense that it doesn't change over time. (Sort of like a stationary current)

 

[Bannon]

I am pretty sure protons would not emit any visible light due to its high energy level. I believe if any radiation emits from it..the electromagnetic fequency would be to high for the eye to perceive, unless it were the pain of your retna burning up..

 

[chroot]

Bannon,

For starters, single particles don't emit photons, because they have no energy states. Only composite particles (like atoms, or the nucleus of an atom) have energy states.

Some nuclei definitely do emit electromagnetic radiation -- in the X- or gamma-ray part of the spectrum.

- Warren

 

[Astronuc]

The term X-ray is reserved for the EM radiation coming from electrons in the K or L shells of the atom, that is the photons have sufficient energy to penetrate.

The term gamma-ray is reserved for EM radiation from the nucleus and subatomic particles.

Visible light energy is in the range of 2 - 3 eV.

Brief overview of EM spectrum - http://csep10.phys.utk.edu/astr162/lect/light/spectrum.html

 

[Rade]

Protons and neutrons are believed to be composite systems of three quarks. http://hyperphysics.phy-astr.gsu.edu/hbase/particles/proton.htmlStructure Evidence from Deep Inelastic Scattering http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/scatele.html#c1

There is also evidence that ~5% of magnetic moment of proton results from presence of strange quark--thus it is more complex than (uud) quarks = proton--see these links:http://focus.aps.org/story/v16/st7
http://prl.aps.org/abstract/PRL/v95/i9/e092001

Also is the presence of the "proton sea"--see this from Science:

PARTICLE PHYSICS: Exploring the Proton Sea
Science; 1/22/1999; Watson, Andrew

Recent studies probing deep inside the proton are revealing much more than the expected three quarks and the gluons holding them together. Physicists are finding a churning and bubbling sea of "virtual" particles that pop into existence for an instant, then disappear again, bathing the more enduring components in a quantum flux. The more researchers study this sea, the more surprises it throws up, but charting it is important for future experiments: The world's most powerful particle accelerator, the Large ...

 

[marlon]

We theorize the structure of atome pretty good, as in, the protons and neutrons bunched togeather in the center with the electrons revolving around. But do we have any ideas on what a proton particle looks like? List any links if you know any, thannks.

THIS is what a proton, or neutron looks like when you operate on them.

You always have three quarks that interact with each other via the strong force by emitting and absorbing gluons. In between these three quarks you have a gazillion of virtual quark/anti-quarkpairs (the socalled dynamical quarks) that pop up and die shortly after.

These quarks are responsible for the fact that the protonmass is BIGGER than the sum of the three quarkmasses. This is contrary to the atomic nuclei masses being smaller than the sum of all proton and neutron masses that are involved because of the negative binding energy.

marlon

 

[arivero]

These quarks are responsible for the fact that the protonmass is BIGGER than the sum of the three quarkmasses. This is contrary to the atomic nuclei masses being smaller than the sum of all proton and neutron masses that are involved because of the negative binding energy.

The keyword is "glue". It is said that most of the mass of the proton comes from the glue.

 

[marlon]

The keyword is "glue". It is said that most of the mass of the proton comes from the glue.

Well, but, the glue and virtual pairs are directly related to each other, so how can you split up their influence ?

marlon

 

[Mk]

The keyword is "glue". It is said that most of the mass of the proton comes from the glue.

Glue doesn't taste as good as it looks.

For starters, single particles don't emit photons, because they have no energy states. Only composite particles (like atoms, or the nucleus of an atom) have energy states.

What about spontaneous emission?

 

[Gokul43201]

What about spontaneous emission?

That post was by chroot, not Zz.

Spontaneous emission from where ?

 

[Astronuc]

Glue doesn't taste as good as it looks.


What about spontaneous emission?

Of what? Gamma-rays? Or other particles.

Like ZapperZ indicated a single particle, e.g. a proton does not emit anything. Even deutrons (pn) do not spontaneously emit gamma-rays, since it is fairly stable, and even alpha particles (2p,2n) are stable, so they don't emit spontaneously. Atomic nuclei (with numerous protons and neutrons) can be 'bumped' into higher energy states, and the excited stated will decay by gamma-emission.

 

[Rade]

Like ZapperZ indicated a single particle, e.g. a proton does not emit anything

But, a "proton" may "decay" via beta (+) or positron decay, whereby a proton is converted into a neutron. A common example is Carbon-11, used in PET scans in medical sciences. The beta (+) emitted from Carbon-11 decay thus joins with an electron (-) from human tissue to yield gamma rays. So, are we saying then that there are not "single protons" within Carbon-11 isotope -- since a single particle does not emit anything ?

 

[ZapperZ]

Whoa!

I get "credited" for saying something in this thread even when I never participated, till now! Amazing!

:)

Zz.

 

[Orion1]

But do we have any ideas on what a proton particle looks like?

Affirmative, based upon classical nuclear theory, a proton is an extremely dense and spherically symmetric point-like particle.

The proton's spherically symmetric volume geometry is supported by hard nuclear scattering cross sectional experiments.

Average Proton density:
$$\boxed{\rho_p = \frac{3}{4 \pi M_0 r_0^3}}$$
$$M_0 = 6.022 \cdot 10^{26} \; \text{amu} \cdot \text{kg}^{-1}$$ - kilo Avogadro's number
$$r_0 = 1.2 \cdot 10^{-15} \; \text{m}$$ - empirical constant

Imaging the proton with particles or photons with wavelengths of the order $$r_p = \overline \lambda_{\gamma}$$ would produce a 'fuzzy' interference patterned image similar to that of a probability cloud.

Reference:
http://en.wikipedia.org/wiki/Proton

 

[reilly]

During the late 1950s and early 60s, Robert Hofstadter did a series of brilliant electron scattering experiments with the old Stanford Linear Electron Accelerator. And, his work conclusively showed that protons and neutrons were not point particles, but instead had an internal structure, which was described by the so-called electromagnetic form factors. His work established the rms electric and magnetic radii as 0.7 X 10-13 cm. , and consequently that nucleons were not point particles.

While this is in the same order of magnitude ball park as the nuclear scattering radii, there'e no strong reason to suppose that the two quantities are equal. The scattering circumstances are very different; the electron scattering experiments are at much higher energy than typical nuclear interactions. They involve different forces -- electromagnetic vs. strong.

Nowadays, electron proton scattering is still alive and well at Jefferson Lab in Virginia. A nice summary of current thinking on nucleon structure, including non-spherical shapes can be found in:

http://www.azonano.com/details.asp?ArticleID=409

Regards,
Reilly Atkinson

 

[Andrew Mason]

Bannon,

For starters, single particles don't emit photons, because they have no energy states. Only composite particles (like atoms, or the nucleus of an atom) have energy states.

Some nuclei definitely do emit electromagnetic radiation -- in the X- or gamma-ray part of the spectrum.

- Warren

Would you consider an electron-positron pair a composite particle? If so, can it be said that this composite particle emits the two gamma rays that result from its annihilation?

AM

 

[SpaceTiger]

There seem to be a lot of correct but unqualified facts being thrown around here, so maybe we could try stepping back a little. One of the main points of contention seems to be the following statements:

For starters, single particles don't emit photons, because they have no energy states. Only composite particles (like atoms, or the nucleus of an atom) have energy states.

This makes sense if chroot (not ZapperZ ) is referring to free particles that don't change their identity after radiating. A free electron, for example, cannot spontaneously radiate. To see this, just boost to its rest frame and try to conserve both momentum and energy after photon emission. In order to conserve momentum, the electron must begin moving in the direction opposite the emitted photon (zero net momentum). However, a moving electron has more energy than a stationary one, so the initial state (stationary electron) and final state (moving electron plus photon) do not have the same energy. In the absence of an external energy source (i.e. for a free particle), this is not possible.

However, if the particle is composite, then the interactions of its components can have energy. This means that the effective mass of the composite particle (say, a hydrogen atom) can be different after photon emission. The "moving atom plus photon" can, in some circumstances, have the same energy as the initially stationary atom.

This is all well and good, but I'm not sure it explains why a free proton can't radiate. After all, we have already determined that the proton is, in fact, a composite particle (made of quarks and gluons). It is still an open question in the physics community as to whether or not a proton can decay (producing other particles that can decay into photons), but I don't think I've ever heard anyone discuss "energy states" for the proton. Why is this?

 

[samalkhaiat]

This is all well and good, but I'm not sure it explains why a free proton can't radiate. After all, we have already determined that the proton is, in fact, a composite particle (made of quarks and gluons).

It seems that (at length scale ~0.1fm) the constituent quarks do not get excited (or bothered) by each others em-fields. So no radiation is expected from their bound state (the proton).
One can also say;
since the quarks "inside" the proton are almost "free", therefore they can not emit photons.

It is still an open question in the physics community as to whether or not a proton can decay (producing other particles that can decay into photons),

One should distinguish between decay processes and radiation processes, specially when the decay is an em-process.
It is better to agree on the following:
a process that changes the identity of the system is (called) a decay process. And call radiation process (emiting photons), a peocess that keeps the system intact.

For example;

$$\pi^{0} \longrightarrow 2 \gamma$$

is an em-decay process ( the pion is gone),
but

$$e^{-} + (Z,A) \longrightarrow e^{-} + (Z,A) + \gamma$$

is a radiation process ( the electron and the nucleus are still there after radiation).

I don't think I've ever heard anyone discuss "energy states" for the proton. Why is this?

The problem of bound states in QCD is still unsolved.
If one knows the exact form of the q-q potential, then (with great patience) one could find the energy levels (states) of proton and all other hadrons by solving Dirac (or even Schrodinger) equation.
People have "experimented" with many potentials, the frequently used potentials (adjusted to fit the observed states of the charmonium and bottomium) are

$$V(r) = -\frac{1}{2r} + 0.2 r$$

$$V(r) = 0.7 ln(r/2)$$

However, even the exact dependence on the quark separation (r) does not solve the 2-body(meson) or 3-body(baryon) problem completely. as well as (r) the potential should also depend on the ordinary and the unitary spins of the quarks. Well, the story does not end here. The exact potential should account for the fact that the proton "lives" as 5-body system for a considerable length of time;

$$p = uudq\bar{q}$$

So, I do not think we will live to see the

$${}^{2S+1}L_{J}$$

(energy) states of the proton.

There is another model for the q-q potential. Feynman et al.(1971) considered a relativistic hadron consisting of 2 or 3 quarks bound together by a covariant harmonic oscillator potential. It was shown (Kim & Nos 1977) that the Lorentz-squeezed wave function of the covariant oscillator can be used to resolve a paradox in the parton model of hadrons;( here the OP can see what the proton looks like)

When the hadron (meson or baryon) is at rest, it appears as a "bound state" of 2 or 3 quarks. When it moves with its velocity close to that of light, the hadronic matter becomes concentrated along one of the light-cones, with wide-spread distributions in both space-time and momentum-energy. As a consequence, the hadron appears as a collection of a large number of "free" partons.
So for a stationary observer, the proton appears as a bound state of 3quarks. But, for an observer who is moving very fast, the same proton appears as a plasma of free partons
Obviously, the two observers will quarrel over the structure of the proton.
The Lorentz-squeezed wave function of the covariant harmonic oscillator (model of potential) settles this quarrel (the paradox).


Feynman R.A., Kislinger M and Ravndal F.(1971) Phys.Rev. D3, 2706-2732.
Kim Y.S. and Noz M.E.(1977), Phys.Rev. D15, 335-358.


regards

sam

 

[captain black]

The problem of the shape of hadrons and more specially of the nucleons was firstly posed by S.Glashow in 1979.This problem is of fundamental interest.The conclusions of the research till now is that the proton is not spherical but probably looks like an ''egg''.The mechanismus that causes this distortion are the chromotensor (colortensor) forces between the quarks and the pion cloud.The reaction used to study the hypothesis of the distortion of hadrons is γ+N->Δ

 

[SpaceTiger]

One should distinguish between decay processes and radiation processes, specially when the decay is an em-process.

Well, yes, that's what the italics were meant to do.

The exact potential should account for the fact that the proton "lives" as 5-body system for a considerable length of time;

$$p = uudq\bar{q}$$

How was this determined experimentally?

 

[Farsight]

Can anybody tells me what a gluon "looks" like? I'm looking for a nice simple concept.

 

[Meir Achuz]

A gluon is the photon of QCD. The differences are:
1. There are 8 gluons.
2. Gluons have direct gluon-gluon interactions.
3. Because gluons have color and color is confined, free gluons have not been observed.

 

[jtbell]

The exact potential should account for the fact that the proton "lives" as 5-body system for a considerable length of time; $$p = uudq\bar{q}$$

How was this determined experimentally?

One way is deep inelastic scattering of neutrinos. For example, when you scatter neutrinos off of nuclei (protons and neutrons), you get events from interactions with strange quarks. When I was a grad student around 1980, I worked on a neutrino experiment that among other things studied the "quark structure functions" of nucleons. There were contributions from "valence quarks" (the qqq part) and "sea quarks" (in the "sea" of virtual $q\bar{q}$ pairs surrounding the valence quarks).

 

[Farsight]

Thanks Meir. I have some knowledge of this from various books and web pages like the one below.

http://webphysics.davidson.edu/mjb/qcd.html

"Both quarks and gluons carry a type of charge called 'color.' Like electric charge, color charge is always conserved. But unlike the electric charge, the color charge (the chromo in chromodynamics) comes in six varieties, three colors and three anti-colors... There are 8 gluons as they each have one of the eight possible color/anti-color combinations."

But I've never been able to get a simple concept of a gluon. You mentioned photon. I have a simplistic mental picture of a photon being a traveling warp in a rubber-tent universe, where a tent pole "charged particle" has just been kicked.

Is this a useless analogy, and if not is there some other analogy wherein a proton is eg a small three-dimensional rubber pocket?

 

[Farsight]

Come on guys. Somebody give me an image of a gluon, that starting-point component of the proton. Otherwise I'll start thinking thinking that a proton is a rubber punch bag hanging down from my rubber tent.

 

[samalkhaiat]

How was this determined experimentally?

I am a theoretician, I do not know how to do experiments .
What I do know is that the probability of finding a proton in each of the configurations,

$$uudu\bar{u},uudd\bar{d},uuds\bar{s}$$

is approximatly 5%. This explains the small discrepancies between the measured proton magnetic moment and that predicted by the simple quark model with its "valence" quarks uud.

I also know how one can calculate the average number of "sea" quarks from the "experimentally" extrapolated graph of the proton structure function.

With or without experimental verification, We know that the quark vacuum is polarized inside hadrons. We also know (with no experimental indication) that quarks have hidden degree of freedom (colour). I call such knowledge as theoretical facts.

regards

sam

 

[SpaceTiger]

With or without experimental verification, We know that the quark vacuum is polarized inside hadrons. We also know (with no experimental indication) that quarks have hidden degree of freedom (colour). I call such knowledge as theoretical facts.

Theory without experimental support is just philosophy, so I don't think this is the answer you want to give. Color is indeed based upon experimental evidence -- for example, the lack of qq hadrons mentioned in another thread. It is only fact insomuch as the model (or models) that predict it (such as QCD) hold up under experiment.

In your statement:

The exact potential should account for the fact that the proton "lives" as 5-body system for a considerable length of time;

I was having a little trouble understanding how this fit in with the conventional picture of hadron structure that jtbell described. When you say that it lives this way for a considerable length of time, do you mean that the five-quark state is an intermediate one in the process of hadronization? If so, how can this be based solely upon theory if the process of hadronization is not fully understood?

Or do you simply mean what you said in your last post, that there is a non-negligible probability of finding the proton in the five-quark configuration due to the sea of virtual pairs? If you're simply referring to the structure function of the proton, then I'm already familiar with the experimental evidence.

 

[Farsight]

..We also know (with no experimental indication) that quarks have hidden degree of freedom (colour)...

Sound like dimensions to me. Like the height width and depth of my rubber bag.

 

[Farsight]

This thread is entitled "What does a proton look like".

So can anybody offer a concept for a gluon, one of the components of the proton?

Something better than the s t r e t c h in a rubber pouch proton with height width and depth, hanging down from a rubber-tent universe? How about a rubber ball proton? How about bubble wrap?

Please?

 

[Imop45]

Pictures of atoms.

Hi, sorry for posting this, but I was wanting to know if there is an actual picture of an atom. Picture as in a scan or something like that. Has a Microscope even been made that can see that small a structure?

 

[Farsight]

imop45: No. But search google on scanning tunneling microscope. This basically "feels" the atoms to create an image. But it isn't a detailed image. An atom shows as a bump.

http://physics.nist.gov/GenInt/STM/stm.html

Maybe somebody knows better. Also check out crystallography.

http://en.wikipedia.org/wiki/Crystallography

 

[Farsight]

So can anybody offer a concept for a gluon, one of the components of the proton? Something better than the s t r e t c h in a rubber pouch proton with height width and depth...

Come on guys, somebody say something. Because now I'm onto electrons, and they seem to be standing-wave electric rubber onion rings. Oh yeah, with a moebius strip twist.

Help!

 

[samalkhaiat]

Theory without experimental support is just philosophy

No, It is just a theory. Supergravity is not philosophy. Any way, I meant to say that experimental physics is not a business of mine. And I do not find it interesting to talk about the various lepton-nucleon DIS experiments.

Color is indeed based upon experimental evidence -- for example, the lack of qq hadrons mentioned in another thread.

The introduction of the colour degree of freedom "was" based purely on theoretical ground, without it the $(3/2)^{+}$ decuplet baryon wavefunctions would violate Pauli principle. This is why it was called the colour hypothesis. The story here is similar to that of the neutrino hypothesis. Do you see what I meant by theoretical "facts"; we know "it" is there even though experiment does not show "it".
At that time, there was no experiment that led us to the introduction of colours.
The absence of qq hadron does not mean or imply that quarks carry colour. However, if the quark does carry colour, then the absence of qq means that colour is a hidden degree of freedom, i.e. coloured hadrons are not observable. This is why (after the introduction of colour) it was "assumed":
"only colour-singlets are observable"
But what is it about colour that makes it a hidden degree of freedom? I wish, I know the answer. It seems that the colour-singlet conjecture is not derivable from the mathematical tools of the theory.
We still do not know why the quarks can not confine themselves in a bound state of coloured hadrons like qq. But we know why we do not know: the exact form of q-q potential (which we do not know) should be able to rule out such bound-states. That is if, it is meaningful to talk about such thing as the "exact q-q potential".
We now know several direct pieces of experimental evidence which support the colour hypothesis. The first comes from the analysis of the $\pi^{0}$ lifetime (as discussed by many textbooks), this is "wrong" by roughly a factor $N^{2}=9$ without the inclusion of colour. Further support comes from measurements of:

$$R_h = \sigma ( e^{+}e^{-} \rightarrow hadrons) / \sigma (e^{+}e^{-} \rightarrow \mu^{+} \mu^{-})$$

with the inclusion of the colour factor 3, the calculations shows R = 11/3 in reasonable agreement with the data.

I was having a little trouble understanding how this fit in with the conventional picture of hadron structure that jtbell described.

I thought my statement was clear and simple

do you simply mean what you said in your last post, that there is a non-negligible probability of finding the proton in the five-quark configuration due to the sea of virtual pairs?

O Yes, this is what I meant, and this is (it seems) exactly how jtbell understood my statement.



regards

sam