 confined within a region 0.87 femtometers wide — or is it 0.84?)
The proton's three quarks are (mostly) confined within a region 0.87 femtometers wide — or is it 0.84?
Image: Flickr/Argonne National Laboratory
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One of the Universe's most common particles has left physicists completely stumped. The proton, a fundamental constituent of the atomic nucleus, seems to be smaller than thought. And despite three years of careful analysis and reanalysis of numerous experiments, nobody can figure out why.
An experiment published today in Science only deepens the mystery, says Ingo Sick, a physicist at the University of Basel in Switzerland. "Many people have tried, but none has been successful at elucidating the discrepancy."
The proton's problems started in 2010, when a paper published in Nature seemed to show that the particle was 4% smaller than originally thought. Researchers began with a target of hydrogen, an atom that consists of one proton and one electron. When they bombarded the hydrogen with muons — heavier cousins of electrons — from a particle accelerator, a muon would occasionally replace an electron. Probing the muonic hydrogen with a laser yielded a high-precision measurement of the proton's size. The problem is that the measurement differed from those obtained by two other methods by 4%, or 0.03 femtometers (fm). That's a tiny amount — 1 fm is 0.000000000001 millimeter — but is still significantly larger than the error bars on either of the other measurements.
The latest experiment also used muonic hydrogen, but probed a different set of energy levels in the atom. It yielded the same result as the Nature paper — a proton radius of 0.84 fm, says Aldo Antognini, a physicist at the Swiss Federal Institute of Technology Zurich in Switzerland and an author of both muonic papers. The second measurement "is totally compatible with the previous value," he says.
But it is still not compatible with the measurements taken by non-muonic techniques, says John Arrington, a nuclear physicist at Argonne National Laboratory in Lemont, Illinois. Errors in the muon-based measurements of the proton radius are unlikely to be to blame, Arrington says, and yet it seems equally unlikely that all the other measurements are wrong, too.
Perplexing puzzle
One possibility is that Antognini's team has inadvertently discovered new physics. It is the only one to use muons to probe the proton — the others all used electrons, and there is a small possibility that muons interact with protons differently from electrons. The effect would have to be small, or it would also show up in other places, such as the Large Hadron Collider, the big particle accelerator near Geneva, Switzerland.
Arrington and Sick both have their doubts. "I'm a big believer in our understanding of physics," Arrington says. Given the power of existing theories, Sick says, the idea of fundamental differences between muons and electrons is "sort of hard to imagine".
But equally hard to imagine is what might have gone wrong. Experimentalists have combed back over their data. Theorists have recrunched their equations. There could be a problem with the models used to estimate the proton size from the measurements, but so far, none has been identified. "Many of the ideas that have been stated have all been looked at in more detail," Sick says. "Nobody has come up with a clear result."
This article is reproduced with permission from the magazine Nature. The article was first published on January 24, 2013.
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61 Comments
Add CommentA new very high precision measurement of the proton radius is 5-sigma lower than QED-based expectations.
Reply | Report Abuse | Link to thisThe QED-based value is 0.877 fermi to 0.9 fermi.
The new measurement indicates that the proton radius is 0.84 fermi.
Decades ago Discrete Scale Relativity predicted that the proton radius would equal about 0.81 fermi, based on the Schwarzschild metric and the corrected value of G. Going to the more realistic Kerr-Newman metric gives a slightly higher value of 0.814 fermi.
http://www.ejtp.com/articles/ejtpv6i22p167.pdf
So on the proton radius test, Discrete Scale Relativity not only competes well with QED, it actually beats QED and gives a more accurate retrodiction.
There is a whole new way to understand the cosmos.
Want to enter the 21st century?
Robert L. Oldershaw
http://www3.amherst.edu/~rloldershaw
Discrete Scale Relativity/Fractal Cosmology
"How can physics live up to its true greatness except by a new revolution in outlook which dwarfs all its past revolutions? And when it comes, will we not say to each other, 'Oh, how beautiful and simple it all is! How could we ever have missed it for so long!'."
John Archibald Wheeler
This puzzle's solution seems too obvious: The size of the proton is measured in terms of electron scattering by the nucleus; the scattering of a muon with a rest mass of 105.7 MeV/c^2 is smaller that the scattering of an electron with a rest mass of 0.511 MeV/c^2. This seems entirely understandable - there must be some unmentioned, unexplained reason why the additional mass of the muon is _not_expected_ by physicists to produce less scattering than an electron - like apples and oranges...
Reply | Report Abuse | Link to thishttp://en.wikipedia.org/wiki/Proton#Charge_radius
http://en.wikipedia.org/wiki/Charge_radius
could be that the muon resonates differently with the proton than an elextron would, possibly causing a suppression or weakening of the strong force.
Reply | Report Abuse | Link to thisSigh.
Reply | Report Abuse | Link to thisThe new muonic atom experiments do not involve scattering muons off protons.
The experiments measure energy-level shifts in the muonic atoms using laser excitation.
A slightly more detailed discussion of the experiments can be found at:
http://www.sciencedaily.com/releases/2013/01/130124140704.htm .
In science, it is always best to fuly understand the the problem before offering solutions.
Robert L. Oldershaw
http://www3.amherst.edu/~rloldershaw
Discrete Scale Relativity/Fracta; Cosmology
There is a very complete web site produced by the research team:
Reply | Report Abuse | Link to thishttps://muhy.web.psi.ch/wiki/
Reply | Report Abuse | Link to thisSometimes people forget that the higher mass of the muon means it orbits closer to the nucleus (than an electron), which in turn means it has a higher probability of present IN the nucleus. This presence in the nucleus will result in increased shielding (between protons) and other higher order QED effects. Are the researches sure they aren't missing any terms that ordinarily can be neglected for electrons but cannot be for muons? Relativistic terms (the closer orbit also means more relativistic effects, not much more, but still more.
Robert L Oldershaw- It's a message board, not a peer reviewed journal. Lighten up.
Thanks so much for the 'expert' explanation:
Reply | Report Abuse | Link to this"The new muonic atom experiments do not involve scattering muons off protons?"
"The rms charge radius is a measure of the size of an atomic nucleus, particularly of a proton or a deuteron. It can be measured by the scattering of electrons by the nucleus and also inferred from the effects of finite nuclear size on electron energy levels as measured in atomic spectra."
http://en.wikipedia.org/wiki/Charge_radius
Might not the much greater mass of the muon not only produce a smaller 'orbit' but smaller shift in its energy level upon photon absorption?
http://www.psi.ch/media/proton-size-puzzle-reinforced
"... The exotic atoms were generated by bombarding a target of regular hydrogen with muons from an accelerator at PSI. Muons behave a lot like electrons, except for their mass: muons are 200 times heavier than electrons. The atomic orbit of the muon is therefore much closer to the proton than the electron’s orbit in a regular hydrogen atom. This results in a much larger sensitivity of the muon’s energy level to the proton size and hence to a stronger shift of the energy levels. Measuring the level shifts is very technologically demanding: muonic hydrogen is very short-lived (muons decay after about two millionths of a second), so the light pulses for the excitation of the resonance have to be fired onto the hydrogen target only nanoseconds after the detection of a muon."
"In the experiment described in the newly published Science article, the energy shift was determined for another transition. This leads to a new measurement of the electric charge radius of the proton. Its value of 0.84087(39) femtometres (1 fm = 0.000 000 000 000 001 metre) is in good agreement with the one published in 2010, but 1.7 times as precise. The discrepancy with existing radius measurements made in regular hydrogen or by electron-proton-scattering, the so-called proton size puzzle, has thus been reaffirmed."
Thanks very much for much better explaining, I think, what I was trying to express...
Reply | Report Abuse | Link to thisthe proton has obviously slimmed down to impress the new wife
Reply | Report Abuse | Link to thisTo be clear I think I'm suggesting something slightly different than what you're saying (unless I'm misunderstanding you). I'm saying the Muon, orbiting closer to the nucleus, has an increased probability of being INSIDE the nucleus (than an electron would). This increased probability of presence of a negatively charged particle inside the nucleus will interfere with the Proton's Electromagnetic Interactions with each other (the muon effectively shields the protons from each other a little in the nucleus). Such an increased in shielding between protons in the nucleus (who repel each other)would reduce the radius of the nucleus a small amount.
Reply | Report Abuse | Link to thisIn other words, I'm not saying that the measurement is wrong, I'm saying the nucleus is probably actually smaller for muonic hydrogen than the regular (electronic) hydrogen atom. In other words, the assumption they are making that the radius of muonic hydrogen and regular hydrogen are the same is wrong, or if they are not making that assumption, then the corrections (QED) they are using to account for muon effects to nucleus radius are insufficient. They're leaving out terms that they shouldn't. Terms that don't matter for an electron calculation but do for muon due to it's increased presence in the nucleus.
That is not to say your statement about the shifted orbital energy levels is incorrect, they are definitely shifted. I just know based having read about this proton story in the past that they account for those orbit shifts in their calculations (it's an obvious detail to them that they account for).
I hope that makes sense. The idea of the electron or muon being present within the nucleus itself catches surprises people by surprise sometimes (though it shouldn't based on the radial solution of the hydrogen atom). You can even see the influence of weak force asymmetry biasing electron orbital transitions because of it in large atoms (check out the old but brilliant paper below)
First-Principle Analysis of Strength of Parity Nonconservation in Atomic Thallium by Relativistic Many-Body Theory; B. P. Das, J. Andriessen, Mina Vajed-Samii†, S. N. Ray‡, and T. P. Das; Phys. Rev. Lett. 49, 32–35 (1982)
Ummm... has anyone noticed that the more recent
Reply | Report Abuse | Link to thisvalue "0.84 fm" is almost exactly 4 times the
reduced proton compton wavelength, which is
about .2103089*10^-15 m. ? Not a clue what
this might mean if true though. :-)
As you indicated and Antognini's team succinctly stated in their 2010 press release:
Reply | Report Abuse | Link to this"Muons are much like electrons, but they are 200 times heavier. According to the laws of quantum physics, the muon must, therefore, travel 200 times closer to the proton than the electron does in an ordinary hydrogen atom. In turn, this means that the muon energy levels are significantly influenced by the proton size."
"Using a specially designed laser, we have measured the energy difference between two muon orbits and from that we have inferred the size of the proton very accurately."
https://muhy.web.psi.ch/wiki/index.php/Main/PR
This article states: "... there is a small possibility that muons interact with protons differently from electrons..." and goes on,
"Given the power of existing theories, Sick says, the idea of fundamental differences between muons and electrons is "sort of hard to imagine"."
Isn't the obvious conclusion that muons DO INDISPUTABLY interact with protons differently than electrons, as proved by their different 'orbital' distances?
Fundamentally, isn't that difference produced by the inertial effect of muon's greater rest mass, and wouldn't that inertial effect also fundamentally affect the measured energy difference between two orbits?
Again, "... we have measured the energy difference between two muon orbits and from that we have inferred the size of the proton very accurately." However, if the inertial differences between muon and electron orbits were not fully considered, they may explain the small differences in inferred proton sizes.
While I don't pretend to be an expert in particle physics it seems to me that you are confusing orbits and atomic orbitals. Gravitational orbits are very much dependent on mass and therefore inertia etc. However the predominant force with atomic orbitals is the coulomb force which is dependent on charGe.
Reply | Report Abuse | Link to thisTherefore it is the wave nature of the particle which must be considered to determine the various energy levels. While the wavelength of the particle has will depend on the mass all of this is still well explained within quantum electrodynamics and other physics.
Yes, your excellent explanation makes very good sense that even I can follow - thanks very much again!
Reply | Report Abuse | Link to thisI certainly don't disagree with your much more knowledgeable assessment, which is why I qualified my concluding statement in my latest comment (which I wrote prior to seeing your latest comment, despite the time difference).
However, isn't there only one proton in the nucleus of the hydrogen atom, eliminating any shielding effect in proton EM interactions?
Do you recall that the researchers not only considered the basic effect of the reduced orbital distance, but also the suggested decrease in energy differences between quantum orbits due to increased inertial effects? I haven't read any very technical descriptions, but I've only seen mention of the smaller orbit as it relates to increased mass, not any decrease in the energy level of each quantum orbital state...
Improved measurement precision might account for some of the difference between derived proton sizes that happens to correspond to the different masses of EM orbitals, but I strongly suspect that the primary factor is an effect of orbital mass that has not been adequately considered. I may not know a lot about physics, but I've debugged many complex information systems over several decades...
Thanks very much for your very helpful insights. Thanks also for you reference, but I can't locate a freely accessible copy - it appears to be too think for me, at any rate.
You certainly know more than I about physics and certainly may be right, but I still suspect mass and inertia must play a role in the energy level of even wave state quantum orbitals. After all, even the tiny inertial mass of neutrinos seems to be a critical factor in limiting their propagation velocity...
Reply | Report Abuse | Link to thisAgain, there's a 1:1 correspondence between measurements of muons rather than electrons and reduced estimation of proton size - that's quite a coincidence!
That was to be expected, I would do anything for a good looking Muon.
Reply | Report Abuse | Link to thisYou wrote "isn't there one Proton....."
Reply | Report Abuse | Link to thisYes, of course your right, and my carelessness can make me look like an idiot at times. Please replace "protons" in my earlier statement with "up and down quarks" and everything I just said still applies. The point I was trying to make before is the Muon has a presence inside the proton itself and shields the quarks electromagnetically from each other resulting in a smaller radius of the proton with muon in orbit about it.
Thank you for pointing out my mistake. I really undercut my credibility by making these simple mistakes sometimes. I'm hopeful when people read my comment and take in this correction, that they realize that what I was saying still would apply.
No, I figured there was a simple explanation, because I can envision how the smaller orbit would increase the frequency at which the muon is manifested within the charge radius of the proton and could affect the actual size, or at least the effective size of the proton derived from the diameter of its charge radius.
Reply | Report Abuse | Link to thisHowever, perhaps more fundamental to the specific measurements of this experiment, isn't it the inertial effect of the muon's greater mass that produces it's smaller orbit?
Might not that same inertial effect reduce the distance produce by a muon quantum jump to a higher energy level, since essentially a greater quanta of energy would be necessary to produce the same energy level attained by an electron?
Since the researchers say "... we have measured the energy difference between two muon orbits and from that we have inferred the size of the proton very accurately," if the energy difference between two muon orbits is slightly different than the difference between two electron orbits (they are attributing 'improved accuracy' of their measurements to some characteristic distinctions between muons and electrons), they may be considering the differences in orbital energy levels to be the result of more precise measurement rather than differences in mass effects.
I hope this is understandable. As I've said, I made a living identifying logic errors producing incorrect results in complex systems I was not very familiar with. I am very familiar with the types of errors that even subject area experts make, suggesting to me this line of investigation...
I do appreciate your expertise in this area, since I essentially have none!
I think I understand your point regarding the orbitals. To explain why that is not likely the issue, you need to understand why Muons orbit the nucleus closer than electrons in the first place. You see, the coulomb potential doesn't depend on mass, only charge, and muons have the same charge as electrons, so the attraction to the nucleus of a muon and an electron in a given orbit is identical.
Reply | Report Abuse | Link to thisHowever, orbits are a balance between the attractive coulomb force and the centripetal force trying to make the moun or electron fly off. For centripetal force, mass does matter, and so the orbit is smaller for a muon as compared to an electron since it takes a higher coulomb potential to offset the higher centripetal force see discussion on bohr orbitals on wiki if confused).
Anyway the point is the "inertial effects" are handled implicitly by the new locations of the orbitals (closer to the nucleus and deeper in the coulomb potential). Your have surmised correctly that it takes more energy to excite a muon to an excited orbital, but what I think you're not realizing is the closer orbits of the muon (again, deeper in the coulomb potential) inherently captures that correction.
I hope that makes sense.
Also, I am far from an expert on this subject and do not want to misrepresent myself here. We are just to people talking.
Sorry, I was sloppy again. I should have said the Centripetal Force is equal to the Coulomb Force for a stable orbit. So when the mass increases (like for a muon as compared to an electron), the centripetal force required to keep it in orbit increases. Since the centripetal force is equal to the coulomb force, the coulomb force needs to increase to keep a stable orbit, which can only happen by moving the muon closer to the nucleus.
Reply | Report Abuse | Link to thisYou may point out "moving the muon closer will increase the centripetal force too". That's true, but not as quickly as it increases the coulomb force (r^-1 vs r^-2). That's why muons orbit closer to the nucleus than electrons.
Everything I said before applies, I just have a tendency to talk loosely and I shouldn't (I shouldn't have said in that post that Centripetal force balances out coulomb force; it's Centrifugal Force that balances out the coulomb force).
Ok, I'm now just correcting myself and will stop now. I'm sorry about my sloppiness. I hope though you understand what I was trying to say and also my own view as to the possible source of the problem.
I still appreciate your greater expertise in our discussion - it's very helpful to me!
Reply | Report Abuse | Link to thisWell, I don't think that difference in the incremental distance of quantum jumps between electrons and muons is fully accounted for in the distance difference of their first orbits, but reviewing equations used in Bohr's model of the atom (per Wikipedia) to derive electron energy levels, I see enough instances of the term for electron mass that I agree its unlikely that these researchers overlooked the mass difference there.
Again though, the researchers are attributing measurement improvements to the properties of muons v. electrons, when the differences might actually represent inherently different results rather than greater measurement precision. As you say, the size of the proton in muonic hydrogen might actually be different than in ordinary hydrogen.
One statement in the current press release puzzles me:
"The atomic orbit of the muon is therefore much closer to the proton than the electron’s orbit in a regular hydrogen atom. This results in a much larger sensitivity of the muon’s energy level to the proton size and hence to a stronger shift of the energy levels."
http://www.psi.ch/media/proton-size-puzzle-reinforced
I don't understand what is meant here by "larger sensitivity" or "stronger shift"...
At any rate, that press release concludes very well:
"... Theorists of various disciplines suggested ways to explain the discrepancy. Very interesting proposals explain the discrepancies by physics beyond the standard model. Other explanations suggest a proton structure of higher complexity than assumed today which only reveals itself under the influence of the heavy muon. New measurements are needed to check on these possibilities..."
Thanks for all your help. There's an old adage that goes something like - 'We haven't answered all your questions, but we're now confused at a higher level, about more important things..." Still, erroneous misrepresentations or oversimplifications in previously effective models are often exposed by applying them to new conditions, such as increased orbital mass...
I like that. I feel I'm ever in pursuit of being confused at a higher level.
Reply | Report Abuse | Link to thisyes, every now and then, we put our legs on one pants at a time. simple mistakes easily understood.
Reply | Report Abuse | Link to thisWhy the physicists should be so impressed by this result (if we neglect the technical part of experiment, which is indeed brilliant) - when they know already, every particle is surrounded by less or more dense coat of virtual quarks (virtual quark-anti-quark pairs)? The similar effect is responsible for Casimir force at different energy density scale. Please note that Riemann manifolds shrink in gravity field - which allows to have larger object inside of smaller one...
Reply | Report Abuse | Link to thisThis difference would be the effect of compacted extradimensions near proton (the same situation could be observed near black holes, which should appear the smaller, the more we approach to them). I hope, these guys considered the fact, muon affects the location of center of mass of proton more, then the electron during its motion around proton - it would be a trivial mistake to forget the classical physics. I.e. the physics, which served for spectroscopic discovery of deuterium in 1932, for example.
Good thought. Me, I was thinking that the shrinkage must be due to processes similar to what happens to guys when they go swimming in cold water.
Reply | Report Abuse | Link to thisAs stated by a previous respondant, who didn't know how to spell "electron", either.
Reply | Report Abuse | Link to this"could be that the muon resonates differently with the proton than an elextron would, possibly causing a suppression or weakening of the strong force."
The interactions between a proton and an electron, or between a proton and a muon, do not have ANYTHING to do with the strong nuclear force because neither electrons nor muons participate in the strong nuclear force at all. Shouldn't that be obvious?
Electrons and muons are both leptons, and leptons do not have anything to do with the strong nuclear force. These two leptons do participate in the weak nuclear force, as can be seen in the beta decay of nuclei in which beta particles are emitted. Beta particles are usually electrons, though the emission of positrons by some artificial nuclei is also possible. (This happens when the nucleus has a excess of protons, hence the emission of a proton turns a proton into a neutron.)
Muons participate in the weak force because muons decay into an electron plus several photons that carry away the excess mass-energy.
So, to reiterate, these experiments do not have anything to go with the strong nuclear force, and that was done deliberately to remove a complication from the experiments. These experiments relied on effects of the electromagnetic force to the exclusion of both of the nuclear forces. Also, the effect of gravity was completely negligible in these experiments with subatomic particles.
D.A.W.
Words and phrases like "muon", "proton", "electromagnetic interaction", "electron", and "neutron" are all common nouns, and they are NOT capitalized unless:
Reply | Report Abuse | Link to this1. They are the first word in a sentence, or
2. They appear in the titles of journal articles or books - such as textbooks.
Capitalizing these word in ordinary text shows a stark lack of knowledge of how the English language works.
Also, "centrifugal force" and "centripedal force" are common nouns, too, and they are not capitalized. Furthermore, anyone who writes of those forces concerning electrons and muons in atoms is using a picture of electrons and atoms (as "little solar systems") that went out of use more than 70 years ago. Such an idea became obsolete and it was replaced by the quantum mechanical thinking of physicists like Heisenberg, Schroedinger, Dirac, and Pauli back during the 1930s and 40s.
The phrase "the orbit of an electron" is misleading because nobody really knows where an electron is when it is bound to an atom. All physicists and chemists can do is to describe its location in probabilitic terms. In other words, they can specify volumes where they are most likely to be within, but that is no guarantee that they really are there.
Please do not even try to understand the results of these experiments with electrons, protons, and neutrons without years of study of probability, random variables, and quantum mechanics. Without that - believe me you will get it wrong every time.
D.A.W.
Proton decay?
Reply | Report Abuse | Link to thisYou are of course correct about the capitalization regarding the forces, I apologize.
Reply | Report Abuse | Link to thisAs for the centripetal force and coulomb interaction, that is how the Bohr Radius is calculated. Although you are correct in saying it is more complicated then that because we are solving the Hamiltonian of wave functions, not particles, it at least provides a physical insight as to why a muon orbits closer than an electron (or if you prefer, why the muon S-shell is closer than the electron S-shell).
You indicate that one should not discuss these matters unless one has study quantum mechanics for years. Although I disagree and believe anyone has the right to discuss these things, the debate is irrelevant since I have a Ph.D. in Physics, specifically calculating the wavefunction properties and energies systems (you can look me up).
There isn't much point in telling you this because you obviously didn't follow the discussion. I was suggesting that because the muon orbits closer to the nucleus, and is more massive than the electron, it has a larger probability of being located within the Proton. There is nothing classical about that last sentence. I indicated that inside the proton the negatively charged muon would shield the positively charged up and down quarks electrostatically from each other.
Since the radius of a proton is a balance between the strong force pulling the quarks together and the electrostatic repulsion of the quarks pushing them apart, and because I'm suggesting the muon, through shielding, is weakening the electrostatic repulsion, what obviously would result is a small contraction of the proton radius, precisely what they are seeing.
I'm sorry if you can't follow that argument, but I assure you it's valid. The theorists involved may have already corrected for it, or the shielding effect may not be strong enough to account for such a strong radial change, but the physics of the argument is sound.
As I recall, there is some question about gravity having repulsive properties at the time of the Big Bang. Seems to me that having the heavier muon, and it being closer to the proton bay be exhibiting the same forces that we theorize existed at the beginning of the universe. That could explain "compression" of the proton.
Reply | Report Abuse | Link to this"The phrase "the orbit of an electron" is misleading..."
Reply | Report Abuse | Link to thisYou'll need to begin the enforcement of your rules with the editors of the journal "Science" and the researchers that produced this study,
"Proton Structure from the Measurement of 2S-2P Transition Frequencies of Muonic Hydrogen", Aldo Antognini, et al., Science 25 January 2013: 417-420. [DOI:10.1126/science.1230016]
Its abstract begins:
"Accurate knowledge of the charge and Zemach radii of the proton is essential, not only for understanding its structure but also as input for tests of bound-state quantum electrodynamics and its predictions for the energy levels of hydrogen. These radii may be extracted from the laser spectroscopy of muonic hydrogen (μp, that is, a proton orbited by a muon)..."
The researchers' website is also quite informative, especially if you read through is ~ 10 pages:
https://muhy.web.psi.ch/wiki/index.php/Main/HomePage
Also refer to:
http://en.wikipedia.org/wiki/Atomic_orbital
Thanks so much for your punitive lecture, but I'm afraid I don't believe you...
(nose pressed against the window glass:) This is great fun, and quite educational...please keep it up.
Reply | Report Abuse | Link to thisDamn it! Where is Richard Feynman when we need him?
Reply | Report Abuse | Link to thisThe Muon is about 200 times heavier than an electron, and bombarding the hydrogen atom with muons, knocking loose an electron and replacing it with a muon probably has interactions with the proton.
Reply | Report Abuse | Link to thisProbably in order for the transfer from electron to muon to take place, the nucleus, or proton, needs to interact directly with the muon.
The quarks in the proton may be compressed together by the muon hitting them, just like a soccer ball when kicked, and then when they bounce back into place, the muon is ejected and replaced again with an electron as the hydrogen returns to it's resting state.
The proton wound be smaller in it's compressed state, but after the muon bounces off, and is replaced with an electron, the proton returns to its normal size and state.
Measuring a proton in a regular hydrogen atom may give a different answer as to proton size, since the proton is compressed when the muon has replaced the electron through muon bombardment.
As an outsider peeking in through the looking glass, some possibly basic questions:
Reply | Report Abuse | Link to this1. are there currently any other particles for which there are similarly discrepant measurements?
2. are the measurements themselves probabilistic?
3. are there currently any proposals for means of measurement not so fare tried?
Something that is "emergent"?, just maybe muons do interact differently? I'm not qualified despite a B.S. Physics '66, but, there is no way to describe/predict accurately how a human being will behave/suffer-disease as an adult despite total (not yet available) knowledge of their genome. Epigenomics anyone? "Self-replicating molecules" cannot be predicted by our current understanding of physics and chemistry. Parthogenesis of a MALE offspring remains problematic for homo sapiens.
Reply | Report Abuse | Link to thisAll the comments so far seem to be looking for corrections to the current experiment. Is it possible that it is correct and the previous measurements were wrong. That seems unlikely but it needs to be considered as well.
Reply | Report Abuse | Link to thisQuoting from this article:
Reply | Report Abuse | Link to this(i)One possibility is that Antognini's team has inadvertently discovered new physics
(ii) "I'm a big believer in our understanding of physics," Arrington says.
Next, kindly permit me to also include what one of the greatest theoretical physicists of all time, Enrico Fermi himself had to say on such issues:
Then [Fermi] delivered his verdict in a quiet, even voice. "There are two ways of doing calculations in theoretical physics", he said. "One way, and this is the way I prefer, is to have a clear physical picture of the process that you are calculating. ..."
A meeting with Enrico Fermi, Freeman Dyson (Institute for Advanced Study, Princeton), Nature 427, 297 (2004)
Further, a pertinent item from Nature:
...atoms shine very brightly for their size: a single atom of calcium, for example, will scatter as much light from a laser beam with a wavelength of 397 nm as a ground glass sphere of 600 times larger radius would. This is because of the phenomenon of resonance – the merest glimmer of incident radiation will cause the atom to 'sing' at its resonant frequency.
The atomic nanoscope, Andrew Steane (University of Oxford, Oxford, UK), Nature 414, 24-25 (1 Nov 2001)
Thus, what we need as a backdrop here is the picture of the quantum mechanical world where all particles of matter, including subatomic particles. are seen as BREATHING ENTITIES,each with a specific frequency (or wavelength) of breathing, which in effect is its natural frequency of vibration. And this frequency becomes the primary factor in any and all particle interactions in nature.
Hence, in the case here of electrons or muons bombarding the proton, the wavelengths of the interacting particles become all too critical, as to how close the 'bullet' could get close to its 'target.' The closer they get to a common (resonant) frequency the shorter the distance between the two at scattering. Since the electron usually 'sings' with the proton at a specific energy. or radial, level of the proton nucleus, and the heavier muon, having thereby a lower frequency, would get scattered (repelled) at a farther distance, despite any increased "ramming" momentum.
No new physics is needed here, but just a return to the good old classical, Newtonian mechanics; one that has taken man to the moon and has brought him also safely back home again.
Please see also:
(1) http://www.sittampalam.net/MassEnergy.htm
(2) http://www.sittampalam.net/Relativity.htm
Thank you all, and Cheers!
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11 &18 RogerPink: Great idea, the muon shields one quark from another inside the proton. Since quarks interact by the strong force, putting something between them would make them get closer together, shrinking the proton. The strong force is proportional to distance rather than the inverse of distance. The strong force has no effect on the muons, so they don't "know" they are inside the proton. The theorists probably did this already.
Reply | Report Abuse | Link to thisRobert L. Oldershaw: What does it mean for a proton to have a "diameter?" It is a fuzzy thing made of 3 quarks. Quarks must have weird "shapes!" I know they said "size" not "diameter." It is some sort of eigen/characteristic size, not like a billiard ball. The protons weren't measured like billiard balls are measured. The size is an "electronic" property. So a proton is a sphere with 3 corners? The more you try to describe it the stranger it gets. The size must be some sort of average over the places where the muon can be, yet the size is not that fuzzy.
If a proton is a black hole but the muon can get back out, the proton is a mixture of a black hole and a white hole.
Could you talk about all of this stuff some more, please?
It is quite interesting, but it does not seem to be a problem here.
Reply | Report Abuse | Link to thisThe presence of the muon obviously causes some changes in the proton even when we do not fully understand why.
RiolderShaw (Commentary 4) is very correct in what he says, it seems to me.
Quite interesting to compress the proton! Just imagine that! How little we know so far.
Obviously (it seems to me clear enough)Vendicar and Matthew (Commentaries 9 & 10) are also right to a good certain extent!
"Robert L. Oldershaw: What does it mean for a proton to have a "diameter?" It is a fuzzy thing made of 3 quarks. Quarks must have weird "shapes!" I know they said "size" not "diameter." "
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For starters, Quarks are probably Ptolemaic (i.e., model-building) fictions.
Consider the near-religious belief among physicists in unobservable hypothetical entities called "quarks". They simply HAVE TO exist, right? Well, read on.
No human in the entire history of this planet has ever observed a "quark". The so-called evidence for "quarks" is based entirely on secondary or tertiary normal decay products and it is INFERRED that they decayed from "quarks".
Likewise the scattering experiments that are interpreted as scattering by unobservable "quarks" have other interpretations, but theoretical physicists desperately wanted "quarks" so they ignored other models.
After Gellman-Mann introduced the "quark" model as a fictional accounting device for particle family numerology, physicists looked everywhere from the deep ocean, to the Moon, to outer space and everywhere in between for free "quarks" with fractional charges. They found not a single one. That was a big problem. So they INVENTED confinement, which is a completely ad hoc way of hiding "quarks" inside hadrons where we can never observe them.
Regarding the "quark-gluon" plasma "evidence", they predicted that it would behave like a weakly interacting gas. The RHIC observational evidence says this prediction was WRONG. The plasma, much to the surprise of theoretical physicists behaved like a strongly interacting fluid, which is much more like what Discrete Scale Relativity anticipates. Of course, given time the theoretical physicists "adjusted" their model to fit the new data, and now they see it as more confirmation of the "quark" fiction. Another epicycle in their Ptolemaic models.
That's particle physics for you: they do not study nature; they tell nature how it should be according to their Platonic model-building fictions.
Non-players in the theoretical physics game are treated like mushrooms: kept in the dark and fed bullshi*t.
And that’s the truth, for once.
Robert L. Oldershaw
Discrete Scale Relativity
http://www3.amherst.edu/~rloldershaw
Fractal Cosmology
Reply | Report Abuse | Link to this"If a proton is a black hole but the muon can get back out, the proton is a mixture of a black hole and a white hole.
Could you talk about all of this stuff some more, please?"
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No one ever said the muon "goes inside the black hole", at least no knowledgeable person.
The muon replaces the electron in an excited atom and for the most part the wavefunction of the electron or muon is far from the nucleus. Yes, the outskirts of the muon's wavefunction may overlap the nucleus, but the overwhelming majority of the muon's mass stays well away from the nucleus.
We should be much less credulous when it comes to ideas that have not been well-tested, but rather are based purely on assumptions or "just-so" stories or unwarranted extrapolations.
As the LHC results have dramatically shown, many of the renowned boffins of theoretical physics have had their collective heads up a place where the light never shines for about 40 years. Lesser mortals and the great unwashed have followed them blindly.
Wake up and study nature for a change!
Robert L. Oldershaw
http://www3.amherst.edu/~rloldershaw
Fractal Cosmology/Discrete Scale Relativity
"The next great awakening of the human intellect may well produce a method of understanding the qualitative content of the equations.” Richard Feynman
BTW - a very interesting suggestion was posted to the Nature article:
Reply | Report Abuse | Link to thishttp://www.nature.com/news/shrunken-proton-baffles-scientists-1.12289
Philip de Louraille said:
"Well, it is time for someone to repeat this experiment and use tau particles instead. If the measured size of the proton is even smaller, then this would ascertain that leptons somehow interact with the constituents of a proton."
However, as I understand the referenced experiment was very difficult since muons decay so quickly, but taus decay much quicker...
Muon mean lifetime 2.1969811(22)×10^−6 s
Tau mean lifetime 2.906(10)×10^−13 s
Yes, unfortunately the Tau particles lifetime is around 20 picoseconds and an electronic transition is around a nanosecond. So, if I understand the experiment correctly, they couldn't get the measurement before the Tau decayed.
Reply | Report Abuse | Link to thisWhy not repeat the experiment with the Hydrogen isotope Deuteron to see if there is a difference there between the expected charge radius (QED) and the experimentally measured charge radius(using muon)?
Thanks for the interesting discussion about this. It has pushed me to read more into this subject. As a consequence I ended up reading about the anomalous magnetic dipole moment of a muon. I was surprised to learn while reading about it that some QCD must be included in that calculation(see link below).
Reply | Report Abuse | Link to thishttp://pdg.web.cern.ch/pdg/2011/reviews/rpp2011-rev-g-2-muon-anom-mag-moment.pdf
That implies that the muon would in fact have a strong force effect on the quarks in the proton. Now this effect would be small due to the fact it requires the creation of virtual hadrons (a rare path), but maybe not negligible. Right now theorists are bad at modeling QCD (see above link again where this is discussed for muon dipole moment). I don't know the scale of such a QCD contribution, but I have to imagine the creation of virtual hadrons in the nucleus (even if rarely) would effect the proton radius. Therefore it could be missing QCD contributions that are ultimately the cause of the discrepancy between muonic and electronic hydrogen proton radius.
I offer this alternative suggestion not because I think my other idea of electrostatic screening was a bad one, I think it definitely occurs. I just would be surprised that the theorists involved would forget to consider it or that it wasn't implicit in the QED calculations they did for the system.
Since these QCD contributions aren't calculated from first principles, and since we assume the theorists involved are competent, QCD seems a more likely source of error.
What I really don't believe is that there is something wrong with QED. It just has been too accurate up till now (see calculation of anomalous magnetic dipole moment of electron).
I'm very glad if our discussions motivated your additional investigation - certainly my low comprehension level would not allow me to have understood the quite possible QCD connection. Your assessment seems very plausible to me.
Reply | Report Abuse | Link to thisAs this article states:
"One possibility is that Antognini's team has inadvertently discovered new physics. It is the only one to use muons to probe the proton — the others all used electrons, and there is a small possibility that muons interact with protons differently from electrons."
The 'new physics' here could just be the error introduced by QCD theoretical limitations... Correspondence between the size 'error' and orbital mass seems to infer that muons do indeed "interact with protons differently from electrons."
Very interesting - good work!
I agree, the new physics here may simply be QCD contributions that don't show up for electrons due to their much smaller mass. That would be the most boring interpretation of the phrase "new physics", which of course is usually how these things work out.
Reply | Report Abuse | Link to thisAs for understanding virtual particles, maybe give this brief SA article a try:
http://www.scientificamerican.com/article.cfm?id=are-virtual-particles-rea
I think it does a good job explaining the concept. When reading it, think to yourself "the larger the mass of a particle, the larger it's rest energy, and thus the higher the probability it can create a larger variety of particle-antiparticle pairs".
With that in mind, if some of the virtual particles of the muon turn out to be virtual quark-antiquark pairs, then for that briefest moment in time when they exist they would interact via the strong force with the quarks in the proton, which of course would result in a reduction of the proton radius. Strong interactions are described through Quantum Chromodynamics, not Quantum Electrodynamics, so the diagrams that describe such contributions wouldn't be included in a QED calculation and would require use of QCD to be included. This naturally would only happen for the small probability of when the Muon was "inside the proton" due to the short distance nature of the strong force interaction. Perhaps not a terribly probable location for the Muon, but then it's unlikeliness of being there may be offset by the strength of the strong interaction it creates when there (through the creation of virtual hadrons). Afterall, they don't call it the "strong" force for nothing.
Plus, when in the proton, the strength of the muon's electrostatic interaction with the quarks of the proton may perhaps spur virtual hadron creation, making it more likely than for muons in a vacuum and thus more relevant than one might expect to these calculations.
Then again, there is a decent possibility that everything I just wrote above is wrong. This is fun.
If the rest mass of a muon is 105.7 MeV/c^2 and that of an electron is .511, does that mean the rest mass of a muon is roughly 200 times that of an electron? That seems like a lot of difference.
Reply | Report Abuse | Link to this.
I have to use a calculator, but 105.7 / .511 ~ 207.
Reply | Report Abuse | Link to thisIngo Sick, a physicist at the University of Basel in Switzerland. "Many people have tried, but none has been successful at elucidating the discrepancy." -- And he's talking about Swiss protons, right?
Reply | Report Abuse | Link to thisThe discrepancy is the same between Swiss cheese and a good, solid Cheddar. Vive la difference! (joking, just joking)
Hi!
Reply | Report Abuse | Link to this"conflicting measuraments"? Could this mean that the assumption of equal protons every when and where no matter the circumstances is not accurate? One of the principles of science is the repeatibility of experiences but in a complex world not always is possible handle all the variables.
Reply | Report Abuse | Link to thisIt takes me a while to follow your reasoning, since I have so little understanding of QED, QCD, QFT, et al. I do have some interest in virtual particles as I think they might relate to vacuum energy, spacetime expansion and static gravitational fields...
Reply | Report Abuse | Link to thisThe old SA article you referenced was quite interesting & helpful (I just had to leave a comment!). This is my primary occupation now - that is, my retirement hobby!
Thanks!
It's a hobby for me as well. I work with QM in molecular systems, not QED.
Reply | Report Abuse | Link to thisAs one hobbyist to another, I recommend the following book:
http://www.amazon.com/Introduction-Elementary-Particles-David-Griffiths/dp/3527406018/ref=sr_1_1?s=books&ie=UTF8&qid=1359770463&sr=1-1&keywords=Elementary+particles+Griffiths
It is a text book, so it is slow reading, but Griffiths has a talent for explaining complicated concepts and it will give you at least an overview of Relativity, QED, QFT, and some other useful stuff to boot.
I recommend buying it used in an older edition where you can probably pick it up for 30-40 bucks.
Best Regards,
Roger
I'm joining late, but there were a lot of interesting ideas and questions, and I wanted to comment on a few of them (leaving out mathematical details)
Reply | Report Abuse | Link to this-How can a fuzzy ball of quarks have a "radius"? While the proton isn't a rigid sphere, there are reasonable ways of getting at its size. For example, you could take the average distance of the all the quarks from the center of the proton. In these experiments, it's not the average distance (R) of the quarks from the center, it's the root-mean-square distance (related to the average R^2) of the electric charge from the center.
-Does the mass of the muon change the size of the proton? The fact that the muon is heavier and closer to the proton does mean that the proton moves around more in response to the muon 'orbiting' around it. These effects are generally small, but they can change the muon's energy levels and so would distort the apparent radius from the measurement. People calculate the effect of all of these corrections so that we can extract the radius. To the best of our understanding, we have precise calculations of these effects - they've all been double and triple checked since the initial muonic measurement. So every physical effect that we know of that relates to the muon mass has been included. If there's some other mass-related effect that causes the difference, it's either something new to us or a complete misunderstanding of some effect that we do include. If either of these is true, it would be incredibly exciting.
-Why not repeat the measurement on deuterium? They have taken data on deuterium, and plan to take data on 3He and 4He. The problem is that nuclei have additional corrections due to the fact that even relatively low energy interactions with the muon can put the nucleus into an excited state. These more complicated nuclear structure effects have to be understood before the radius can be isolated (for hydrogen, it takes much more energy
to 'excite' the proton into another state so these effects are much smaller). These effects can be (and have been) calculated, but it's important to make sure that we understand just how reliable these calculations are before trying to isolate the radius.
The PSI press release gives more details and talks about the measurements that people are doing to try and understand this (including a new measurement using the PSI muon beam to scatter from protons). I predict that we'll be losing sleep over these questions for a little while longer.
https://muhy.web.psi.ch/wiki/index.php/Main/PR1
Hello Johna_6. Thanks for your comments. I will try to be concise in answering your questions in the order you presented them.
Reply | Report Abuse | Link to this1. You make a valid point. When I talk about any system involving QED, QCD, Quantum Mechanics, etc., "fuzzy" is implied. Yes, to clarify, I am talking about the charge density. However, please remember that it is perfectly reasonable to obtain a physical intuition of a quantum mechanical system by visualizing the problem as particles. It's true that saying things like "its a balance between the electrostatic force and strong force" is a terrible over-simplification, but it also provides us with a simple picture to mess around with in order to gain insight as to possible causes of the smaller measured proton charge radius.
2. Yes, I'm quite sure the muon will change the size of the Proton (how much I can't say), at least when present in the S-Shell, D-Shell, etc. (but not the P-shell). Forgive me for saying so, but I feel like you may not be understanding what I'm saying here regarding the muon affecting the proton's charge radius (you seem to suggest I'm making some sort of center of mass argument).
I'm saying the muon is present INSIDE the proton (just like an electron would be). If you have doubts, please recall that it is the electron INSIDE the nucleus of atoms that gives us the Fermi Contact Interaction. Here, look at this link:
http://en.wikipedia.org/wiki/Fermi_contact_interaction
The first sentence should suffice in the above link.
With this idea that an electron can be found INSIDE a nucleus (or in this case INSIDE the proton), realize that a muon, being closer to the proton than an electron, and being more massive than an electron, will have a much larger presence INSIDE the proton than an electron. Again, please, if you doubt me in any way when I say that the electron or muon is found INSIDE the nucleus (or in this case the proton), please read about Fermi Contact Interaction in detail. This the crux of my argument. (I'm proof reading my comment before submitting and I'm worried you might misunderstand me and think I'm suggesting that Fermi Contact Interaction is involved in this Proton Radius problem. That is not what I'm saying. I'm only bringing up Fermi Contact Interaction to prove to you that it is a well established fact that bound electrons (and muons) are found inside the nucleus or in this case the proton(because of their fuzziness). I hope I'm being clear.)
I've exceeded my response character limit and will have to provide a second comment immediately after this.
(Here now is the rest of my response) Part II
Reply | Report Abuse | Link to thisIf you accept that the muon is found INSIDE the proton, it isn't very hard to see that the muon can do all kinds of things like shield quarks from each other electrostatically, create virtual quark-antiquark pairs that interact with the quarks of the proton via the strong force, and otherwise disrupt the balance between the electrostatic forces and strong forces that determine the charge radius of the proton. If this turns out to be the cause (of the proton radius discrepancy), it won't be "new and exciting physics", it will be old physics in a new situation.
3. You know more about this than me. I would suggest using muon transitions farther from the nucleus for these systems (start from an excited state and jump to a higher excited state) to avoid exciting the nucleus. I have no idea how practical this would be to implement. I don't pretend to be an experimentalist. I've too much respect for their art. I yield to your superior understanding of these experiments.
4. It's exciting to think about and discuss these things, but one always should get a good night's sleep (says the guy posting at 12:30).
Thanks very much for the textbook referral - it looks quite interesting!
Reply | Report Abuse | Link to thisI've really enjoyed these discussions and really appreciate you help. I think it would be a very good idea for you to ask a few questions of the study's authors - if you haven't already, please see "Proton Structure from the Measurement of 2S-2P Transition Frequencies of Muonic Hydrogen,"
http://dx.doi.org/10.1126/science.1230016
Best wishes,
Jim
One Clue to the Proton Size Puzzle:
Reply | Report Abuse | Link to thisThe proton radius changes, depending on the particle with which it is interacting.
In this context the standard proton radius need be defined in conditions, where a proton is isolated in space, without interacting with any other particle. In this condition the standard proton radius seems very close to the value obtained in muonic hydrogen experiments.
If this new standard proton radius value be admitted, one solution to the "proton size puzzle" must answer two basic questions:
a) Why the proton increase it size when interacting with an electron in a hydrogen atom?
b) Why the proton maintain the (new) standard radius value, when interacting with the muon to form a muonic hydrogen atom?
The question (a) can be answered, in a context where the electric force that arises between the opposite charges (of the electron and the proton) may be affecting the proton and expanding its radius. Considering the Heisenberg uncertainty principle, with the proton as "observer" of the electron position, the proton also not will "know" where the electron position is. Thus the proton is simultaneously attracted to all positions where the electron might be positioned, which are defined by the orbital wave function. Thus the uncertainty principle could explain that the proton is subjected to a radial force field, which tends to increase its size.
Another solution for the proton size puzzle, considers a change in the physical interpretation of the orbital wave functions. These functions are currently associated probability density of the presence of the electron in a given volume of space. In this new interpretation, the wave functions equations are the same, but its final values (that can be expressed in C/m3) can be associated with an effectively density of electric charge, that exists simultaneously, composing a negative charges membrane which are distributed in space around the atomic nucleus, as defined by the orbital wave function charge densities. This new model has been called by the author as “Electron Membrane Paradigm” (EMP)
See my paper in:
http://vixra.org/abs/1302.0026
One Clue to the Proton Size Puzzle:
Reply | Report Abuse | Link to thisThe proton radius changes, depending on the particle with which it is interacting.
In this context the standard proton radius need be defined in conditions, where a proton is isolated in space, without interacting with any other particle. In this condition the standard proton radius seems very close to the value obtained in muonic hydrogen experiments.
If this new standard proton radius value be admitted, one solution to the "proton size puzzle" must answer two basic questions:
a) Why the proton increase it size when interacting with an electron in a hydrogen atom?
b) Why the proton maintain the (new) standard radius value, when interacting with the muon to form a muonic hydrogen atom?
The question (a) can be answered, in a context where the electric force that arises between the opposite charges (of the electron and the proton) may be affecting the proton and expanding its radius. Considering the Heisenberg uncertainty principle, with the proton as "observer" of the electron position, the proton also not will "know" where the electron position is. Thus the proton is simultaneously attracted to all positions where the electron might be positioned, which are defined by the orbital wave function. Thus the uncertainty principle could explain that the proton is subjected to a radial force field, which tends to increase its size.
Another solution for the proton size puzzle, considers a change in the physical interpretation of the orbital wave functions. These functions are currently associated probability density of the presence of the electron in a given volume of space. In this new interpretation, the wave functions equations are the same, but its final values (that can be expressed in C/m3) can be associated with an effectively density of electric charge, that exists simultaneously, composing a negative charges membrane which are distributed in space around the atomic nucleus, as defined by the orbital wave function charge densities. This new model has been called by the author as “Electron Membrane Paradigm” (EMP)
See my paper in:
http://vixra.org/abs/1302.0026
Protons are not at center in atom but on a very close positive charge cloud outside center. Therefor strong force does not exist.Take the reaction of dark energy inter atomic space. Read theory of DURGADAS DATTA.
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