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Surprise To Physicists -- Protons Aren't Always Shaped Like A Basketball!
Science Daily ^ | 2003-04-08 | Editorial Source

Posted on 04/08/2003 6:16:11 AM PDT by vannrox

Surprise To Physicists -- Protons Aren't Always Shaped Like A Basketball

PHILADELPHIA -- When Gerald A. Miller first saw the experimental results from the Thomas Jefferson National Accelerator Facility, he was pretty sure they couldn't be right. If they were, it meant that some long-held notions about the proton, a primary building block of atoms, were wrong.

But in time, the findings proved to be right, and led physicists to the conclusion that protons aren't always spherically shaped, like a basketball.

"Some physicists thought they did the experiment wrong," said Miller, a University of Washington physics professor. "Even I thought so initially. And then I remembered that it looked like something else I thought was wrong -- our own conclusion in 1995."

In fact, by 1996 he and two colleagues were ready to publish a paper theorizing the angles at which protons would bounce off electrons after collisions in a nuclear accelerator. The measurements would tell a lot about protons' internal electric and magnetic properties, and virtually everyone expected the two effects to cause the same kinds of collisions. But the 1996 paper described collisions that were quite different.

Miller was sure he and his colleagues had gotten it wrong somehow -- until he saw the results of the actual experimental work at Jefferson, a national laboratory in Newport News, Va. Researchers at Jefferson published their initial results in 2000 and updated their findings last year.

What Miller discovered from those results is that a proton at rest can be shaped like a ball -- the expected shape and the only one described in physics textbooks. Or it can be shaped like a peanut, like a rugby ball or even something similar to a bagel.

He was able to use his model to predict the behavior of quarks, and he discovered that different effects of the quarks could change the proton's shape. The model showed that the highest-momentum quarks, those moving nearly at light speed inside the proton, produced the peanut shape. "The quarks are like prisoners walking around in a jail cell. They just are walking very fast, and when they come to a wall they have to turn around and we can see that, indirectly, and measure it," Miller said.

If the quarks are moving more slowly, the surface indentations of the peanut shape fill in and the proton takes on a form something like a rugby ball, or a beehive. The slowest quarks produce the spherical shape that physicists generally expected to see. Another shape -- a flattened round form like a bagel -- is sort of a cousin to the peanut shape with the high-momentum quarks. In the peanut shape, the quarks spin in the same direction as the proton, while in the bagel shape they spin in the opposite direction as the proton.

The variety of shapes is nearly limitless and depends on the speed of the quarks inside the proton and what direction they are spinning, said Miller, who presents his findings today (April 5) during a news conference and an invited talk at the American Physical Society meeting in Philadelphia.

The Jefferson results, he said, are a small piece of the puzzle for physicists who are trying to unify the four forces of nature -- gravity, electromagnetic, strong and weak -- into a "theory of everything" by which they can understand the form and function of all matter. Taking this step, Miller said, allows physicists to make better predictions so other experiments can get even closer to a unified theory, and it provides clues for how to devise those experiments.

The first implication of the Jefferson findings, he said, is that "a bunch of textbooks will have to have some of their pages updated."

Beyond that, he said, it isn't clear right now whether there will be practical implications. However, he tells the story of Michael Faraday, who presented findings in the 1830s on electromagnetic induction but was at a loss to explain the value of his findings. Yet today, the principles he developed are responsible for all the electric generators sending juice from power stations. "You just never know until you understand something where it might lead," Miller said.

Note: This story has been adapted from a news release issued for journalists and other members of the public. If you wish to quote any part of this story, please credit University Of Washington as the original source. You may also wish to include the following link in any citation:

http://www.sciencedaily.com/releases/2003/04/030408085744.htm


TOPICS: Business/Economy; Culture/Society; Extended News; Foreign Affairs; Government; News/Current Events; Philosophy
KEYWORDS: discovery; physics; proton; protons; realscience; science; stringtheory; technology; unusual
This is surprising!
1 posted on 04/08/2003 6:16:11 AM PDT by vannrox
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To: vannrox
I thought that in a high speed accelerator, protons flattened out like pancakes? Also, Doesn't Gell-Mann's liquid droplet model of the nucleus allow for some "floppiness"?
2 posted on 04/08/2003 6:20:11 AM PDT by Flightdeck
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To: vannrox
Kewl!
3 posted on 04/08/2003 6:20:50 AM PDT by The_Victor
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To: vannrox
and wierd. very wierd. one must wonder whether "protonic" shapes might influence nuclear structure in any way, whether certain shapes of "protons" are more closely associated with certain elements than others, and whether the classification of all positively charged nuclear particles as "protons" might need to be revised into a family of diverse particles.
This is quite possibly a revolutionary discovery.
Thanks for posting it.
4 posted on 04/08/2003 6:22:18 AM PDT by demosthenes the elder (The Jesuits TRAINED me - they didn't TAME me)
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To: Physicist
Ping!
5 posted on 04/08/2003 6:25:28 AM PDT by petuniasevan (Non-paying FReepers: "Put your money where your mouth is!")
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To: vannrox
I thought that the point of quantum mechanics is that atomic particles only have certian probabilities of existance at any given point and that the Heisenberg uncertianty principle precludes us from actual true measurement of shape?
6 posted on 04/08/2003 6:25:37 AM PDT by CollegeRepublican
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To: vannrox
Good to know that protons don't just play one kind of ball game.
7 posted on 04/08/2003 6:26:06 AM PDT by Cicero (Marcus Tullius)
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To: vannrox
I seem to remember scattering experiments from about 30 years ago which showed structure within protons. I always had the impression that protons looked like pawn-shop signs, but my sub-atomic intuition is rather miniscule.
8 posted on 04/08/2003 6:29:01 AM PDT by Doctor Stochastic (Vegetabilisch = chaotisch is der Charakter der Modernen. - Friedrich Schlegel)
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To: Flightdeck
I thought that in a high speed accelerator, protons flattened out like pancakes?

To an observer with respect to whom the proton is moving, yes. The shapes discussed in the article are presumably in the proton's rest frame.

Also, Doesn't Gell-Mann's liquid droplet model of the nucleus allow for some "floppiness"?

Yes. I'm not sure why these results are so surprising; as a bound state of three quarks, it stands to reason that the proton would have excited states as well as a spherical ground state. Maybe the excited states are at lower energies than previously assumed ...

9 posted on 04/08/2003 6:36:18 AM PDT by MrLeRoy ("That government is best which governs least.")
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To: demosthenes the elder
one must wonder whether "protonic" shapes might influence nuclear structure in any way, whether certain shapes of "protons" are more closely associated with certain elements than others,

Possibly to both.

and whether the classification of all positively charged nuclear particles as "protons" might need to be revised into a family of diverse particles.

Don't bet on it; these nonspherical shapes are probably just excited states of the three-quark bound state that is the proton.

10 posted on 04/08/2003 6:38:20 AM PDT by MrLeRoy ("That government is best which governs least.")
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To: CollegeRepublican
I thought that the point of quantum mechanics is that atomic particles only have certian probabilities of existance at any given point and that the Heisenberg uncertianty principle precludes us from actual true measurement of shape?

You have to expect a certain amount of oversimplification in a science article written for a general audience. The shapes discussed are presumably the shapes of the surfaces of equal probability density.

11 posted on 04/08/2003 6:39:56 AM PDT by MrLeRoy ("That government is best which governs least.")
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To: vannrox
Protons Aren't Always Shaped Like A Basketball!

No wonder they're so hard to dribble.

12 posted on 04/08/2003 6:47:11 AM PDT by razorbak
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To: MrLeRoy
as well as a spherical ground state
The article seems to imply that a spherical shape isn't the ground state, did I read that right?
If that's the case, does that mean that experiments where you assume that you're bouncing particles off of one another and you're expecting billard ball reactions will be to be re-examined?
13 posted on 04/08/2003 6:48:24 AM PDT by lelio
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To: lelio
The article seems to imply that a spherical shape isn't the ground state, did I read that right?

I don't think so. The article states a sphere is possible, and makes the analogy to prisoners walking around in a cell. The non-spherical shapes arise from the prisoners walking around and bumping into the walls. In the ground state there is no walking - and hence no bumping.

14 posted on 04/08/2003 6:57:59 AM PDT by coloradan
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To: coloradan
In the ground state there is no walking

Not "no" walking, but the slowest walking.

15 posted on 04/08/2003 7:02:29 AM PDT by MrLeRoy ("That government is best which governs least.")
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To: vannrox
In fact, by 1996 he and two colleagues were ready to publish a paper theorizing the angles at which protons would bounce off electrons after collisions in a nuclear accelerator.

This looks funny. A proton has about 1835 times the mass of an electron. Generally it would be the electron that really goes flying after a collion.

16 posted on 04/08/2003 7:08:58 AM PDT by VadeRetro
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To: VadeRetro
More oversimplification; I strongly suspect that electrons and protons were both accelerated.
17 posted on 04/08/2003 7:24:04 AM PDT by MrLeRoy ("That government is best which governs least.")
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To: MrLeRoy
Yes, the momentum of both particles is different, post-collision. The article's wording was funny, however. (" ... The angles at which protons would bounce off electrons ...") When you say you're bouncing cannon balls off of BBs, you imply that the BB is the immovable object and the cannonball is a relatively resistible force.
18 posted on 04/08/2003 7:37:32 AM PDT by VadeRetro
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To: MrLeRoy
sub-nuclear particle physics is too deep for my little mind, so forgive me if these questions are utterly idiotic:
1. Can the "state" of quarks while bound within the structure of a proton be changed without outside influence? ie: can they go from "excited" to "ground" (? I am assuming these states are at some level comparable to the states of electrons) without some external trigger?
2. If they can make such an untriggered change in state, do they emit anything (some quarkish equivalent of a photon)?
3. If they cannot make such a change, des this not mean that a "lethargic quark" proton is a different beastie than a "lively quark" proton? Wouldn't their behaviors and characteristics be different? (again, the question of proton-shape/element correlation arises) Doesn't that mean that they are not really the same things?
19 posted on 04/08/2003 7:38:27 AM PDT by demosthenes the elder (The Jesuits TRAINED me - they didn't TAME me)
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To: MrLeRoy
True. The zero point energy may be why the diameter is non-zero in the ground state. It is certainly why hydrogen atoms are as big as they are (how small they are notwithstanding).
20 posted on 04/08/2003 7:59:59 AM PDT by coloradan
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To: *RealScience
http://www.freerepublic.com/perl/bump-list
21 posted on 04/08/2003 8:08:33 AM PDT by Free the USA (Stooge for the Rich)
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To: VadeRetro
Yes, the momentum of both particles is different, post-collision.

Sorry, I meant I strongly suspect that both protons and electrons were accelerated pre-collision, that is, both were in motion.

22 posted on 04/08/2003 8:10:59 AM PDT by MrLeRoy ("That government is best which governs least.")
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To: demosthenes the elder
1. Can the "state" of quarks while bound within the structure of a proton be changed without outside influence? ie: can they go from "excited" to "ground" (? I am assuming these states are at some level comparable to the states of electrons) without some external trigger?

Yes, any system in an excited state can spontaneously drop to its ground state.

2. If they can make such an untriggered change in state, do they emit anything (some quarkish equivalent of a photon)?

I would expect exactly an electromagnetic emission, whether a real photon or an EM interaction with some other charged particle.

23 posted on 04/08/2003 8:14:25 AM PDT by MrLeRoy ("That government is best which governs least.")
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To: vannrox
The "protonic" shapes are really the "Almond Joy" shape
--- sometimes it's shaped like a nut; sometimes
it's not...
24 posted on 04/08/2003 8:19:05 AM PDT by TRY ONE (")
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To: MrLeRoy
Yes, any system in an excited state can spontaneously drop to its ground state.

I have long been puzzled by that. Nothing comes from nothing. That electrons and quarks can change state from excited to ground without external stimulus offends my mechanistic mindset. ;)

25 posted on 04/08/2003 8:25:40 AM PDT by demosthenes the elder (The Jesuits TRAINED me - they didn't TAME me)
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To: vannrox
Is the claim that protons can have spin angular momentum greater than 1/2?
26 posted on 04/08/2003 8:31:12 AM PDT by Right Wing Professor
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To: vannrox
A proton is a composite particle so I'm not really sure why this is surprising. I believe some of the atomic electron orbits (the first two, I seem to remember) don't make an atom entirely spherical, either.
27 posted on 04/08/2003 8:44:08 AM PDT by Question_Assumptions
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To: coloradan
So this proton looks like a "ball" for lack of a better term, of liquid floating around in a weightless environment (piture the "blobs" of juice, or whatever floating around inside the space shuttle, undulating. make sense?
28 posted on 04/08/2003 9:35:18 AM PDT by Doomonyou
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To: VadeRetro
A proton has about 1835 times the mass of an electron

So they say. But neither has been seen, just inferred. Probably neither, and none of the other elementary particles either, are any more than entries in an algebraic symmetry table.

29 posted on 04/08/2003 9:43:04 AM PDT by RightWhale (Theorems link concepts)
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To: vannrox
The shape of a proton depends on the speed of the quarks inside. Of the four shapes shown here, the spherical shape (lower right) is the shape most physicists expected to find. The peanut shape (top left) is produced by quarks traveling nearly at light speed and spinning the same direction as the proton. (Gerald A. Miller, University of Washington)

30 posted on 04/08/2003 9:55:09 AM PDT by AndrewC
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To: CollegeRepublican
the Heisenberg uncertianty principle precludes us from actual true measurement of shape?

His principle doesn't stop us from measuring anything. The principle says we can't measure everything, as once we measure part of it, we change other things - or the thing we measure. So we can measure shapes, but in doing so we alter characteristics.

31 posted on 04/08/2003 10:55:59 AM PDT by lepton
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To: RightWhale
But neither [proton or electron] has been seen, just inferred. Probably neither, and none of the other elementary particles either, are any more than entries in an algebraic symmetry table.

Electrons and protons are as real as the hydrogen atoms which result when one particle takes up orbit around the other. They're as real as you and I, although you can debate about how real you and I are.

32 posted on 04/08/2003 12:15:47 PM PDT by VadeRetro
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To: CollegeRepublican
You can apply quantum mechanics to the quarks inside a proton and derive their distribution just like you can to electrons inside an atom to derive their distribution (I've never attempted this).

The field where quantum mechanics is applied to the universe in total is called Quantum Cosmology.
33 posted on 04/08/2003 12:34:56 PM PDT by <1/1,000,000th% ((How come we haven't seen any pictures of Ann Coulter lately?))
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To: <1/1,000,000th%
As Mr. Spock would say - Facinating!
34 posted on 04/08/2003 12:41:18 PM PDT by NEWwoman
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To: vannrox
Beyond that, he said, it isn't clear right now whether there will be practical implications. However, he tells the story of Michael Faraday, who presented findings in the 1830s on electromagnetic induction but was at a loss to explain the value of his findings. Yet today, the principles he developed are responsible for all the electric generators sending juice from power stations. "You just never know until you understand something where it might lead," Miller said.

Something we should all remember.
35 posted on 04/08/2003 12:43:16 PM PDT by aruanan
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To: Flightdeck
Each particle behaves as I understand like that: a "water drop" model is probably the best image to show the "waviness" (non-solid, quantumly-controlled) attributes of the particle plus the "solid" idea of a two particles colliding and rebounding.

Plus, the nucleus overall then can be visualized "vibrating" and randomly bouncing into different "droplet" shapes: fission can occur when the nuetrons get too far apart and reduce the strong bonds holding everything together. A pure solids model doesn't communicate the idea of ission breaking up very well.
36 posted on 04/08/2003 12:48:14 PM PDT by Robert A. Cook, PE (ABBCNNBCBS (continue to) Lie!)
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To: NEWwoman
(Eyebrow rising.)
37 posted on 04/08/2003 12:51:13 PM PDT by <1/1,000,000th%
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To: <1/1,000,000th%
Like Spock's ears, you make a good point.
38 posted on 04/08/2003 1:00:17 PM PDT by NEWwoman
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To: VadeRetro
Electrons and protons are as real as the hydrogen atoms

If you say so. I have never known anyone before who has actually seen an electron. JJ Thompson's charge measurement experiment was interesting, but he never saw an electron either, not that he claimed anyway.

39 posted on 04/08/2003 1:05:22 PM PDT by RightWhale (Theorems link concepts)
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To: vannrox
In the peanut shape, the quarks spin in the same direction as the proton, while in the bagel shape they spin in the opposite direction as the proton.

Isn't the proton's spin simply the sum of the spins of it's quarks?

40 posted on 04/08/2003 1:16:54 PM PDT by edsheppa
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To: MrLeRoy
JLab, formerly known as CEBAF, is an electron accelerator. I suspect the protons were in a fixed target.
41 posted on 04/08/2003 1:43:29 PM PDT by Cooter
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To: vannrox
mark to read later
42 posted on 04/08/2003 2:06:59 PM PDT by CyberCowboy777 (In those days... Every man did that which was right in his own eyes.)
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To: RightWhale
I have never known anyone before who has actually seen an electron.

I have never known anyone who has actually seen the wind.

43 posted on 04/08/2003 2:32:58 PM PDT by MrLeRoy ("That government is best which governs least.")
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To: MrLeRoy
I have never known anyone who has actually seen the wind.

That's more like it. Like my philosophy prof likes it. Like Socrates liked it. I've never seen these three famous dimensions of space, or four if you count time. Never seen time either. Is time hourglass-shaped? Are protons antisymmetric spin sets?

44 posted on 04/08/2003 2:38:54 PM PDT by RightWhale (Theorems link concepts)
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To: NEWwoman
When we were kids my dad used to rush us home to see Star Trek when it was originally broadcast on network TV (NBC?). My brothers and I all learned the "raised eyebrow". ;)
45 posted on 04/08/2003 3:40:29 PM PDT by <1/1,000,000th%
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To: <1/1,000,000th%
Oh, yes. It dates me. I remember as a kid seeing Star Trek's first run on our Black and White TV. (Color sets were a luxury.) During college, we gathered in the dorm TV room to watch the reruns on cable and it was in color.
46 posted on 04/08/2003 4:09:40 PM PDT by NEWwoman
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To: edsheppa
Isn't the proton's spin simply the sum of the spins of it's quarks?

If they behave like atoms, there's also an orbital contribution.

47 posted on 04/08/2003 4:19:08 PM PDT by Right Wing Professor
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To: Right Wing Professor
I didn't understand your post so I searched around the web a little and found this.
When quark-gluon field theory (QCD) corrections are taken into account, the analysis of all published data indicates that quark spins account for only about 30% of the nucleon spin. The origin of the remaining fraction of the spin is not yet understood. Taken at face value, the recent SMC and E143 data indicate a significant contribution to the nucleon spin from the strange quarks and antiquarks with a net polarization opposite to that of the nucleon. This disagrees with the predictions of naive quark models, such as those proposed 20 years ago by J. Ellis and R. Jaffe as a benchmark for the subsequent data.

One possible interpretation is a large contribution from the AdlerBellJackiw "axial anomaly" by which a quantum effect destroys a classically conserved current. This effect is expected to be small unless there is a large gluon polarization. The small quark spin fraction and the polarization of the strange quark sea can alternatively be explained naturally in a class of approximate models of QCD in which the spin-1/2 nucleon corresponds to a sort of "knot" in the field of pions (topological soliton). Thus, to understand the spin structure of the proton, one has to take into account an unexpectedly large effect of either the gluon spins or the orbital angular momentum of quarks and gluons.

That said (and I only understand it roughly), what is mysterious to me is how these disparate bits add to the quark spins to equal exactly +-1/2. If the orbital motion of the quarks increases there must be a ledger balancing change in spin somewhere else.
48 posted on 04/08/2003 9:09:35 PM PDT by edsheppa
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Note: this topic is from April 8, 2003. Thanks vannrox (wherever you are).

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49 posted on 08/26/2010 5:38:17 PM PDT by SunkenCiv (Democratic Underground... matters are worse, as their latest fund drive has come up short...)
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