The Incredible Shrinking Proton

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Discussion Overview

The discussion centers around the recent measurements suggesting that the proton may be 4% smaller than previously established sizes. Participants explore the implications of these findings, the potential for new physics, and the challenges in measurement accuracy and theoretical interpretation.

Discussion Character

  • Debate/contested
  • Exploratory
  • Technical explanation

Main Points Raised

  • Some participants express curiosity about the reasons behind the proton's apparent size reduction and speculate on the implications if future experiments confirm this result.
  • Concerns are raised regarding the estimation of systematic and random errors in measurements, suggesting that error bars may be underestimated.
  • One participant argues that the reported size of 1.082 femtometers may not be significant, emphasizing the need to understand quark confinement and the role of gluons and sea quarks in the proton's structure.
  • Another participant highlights the variability in proton radius measurements and suggests that differing results could indicate either measurement errors or the possibility of new physics affecting muon-proton interactions.
  • A later reply proposes that while new physics could be a factor, the more straightforward explanation might involve issues in theoretical calculations that relate measured values to the proton radius.

Areas of Agreement / Disagreement

Participants do not reach a consensus; multiple competing views remain regarding the interpretation of the measurements and the potential implications for physics.

Contextual Notes

Participants note limitations in measurement accuracy and the complexity of theoretical calculations, which may affect the understanding of the proton's size and structure.

sanman
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Some researchers seem to have measured the proton as being 4% smaller than previously thought:

http://www.nature.com/news/shrunken-proton-baffles-scientists-1.12289

What is the reason for this?

This is the second time the experiment has been conducted. If it is carried out yet again, and yields the same strange result, then what are we to make of it?

Is there any speculation on what is going on here?
Is it possible that muons have some previously unknown interaction with the proton? Otherwise, what else could it be?
 
Physics news on Phys.org
Systematic and random errors are hard to estimate. People always underestimate their error bars.
 
Some researchers seem to have measured the proton as being 4% smaller than previously thought:

The 1.082 femtometer size of the proton is a red herring. It doesn't really mean much. I mean, it means something, of course, but the real issue is what the hell is quark confinement, what are all these gluons doing in my soup?, and can someone please tell me what 2/3 charge means? I mean for god's sake. If that's not enough, two words...sea quarks.
 
DiracPool said:
The 1.082 femtometer size of the proton is a red herring. It doesn't really mean much. I mean, it means something, of course, but the real issue is what the hell is quark confinement, what are all these gluons doing in my soup?, and can someone please tell me what 2/3 charge means? I mean for god's sake. If that's not enough, two words...sea quarks.

It is still an issue however that different measurements seem to give different (charge) radii of the proton. The pessimist would say that there is something wrong with the measurement or error treatment, whereas the optimist would say that it might be due to new physics which affects muon-proton interactions differently. It might not have much to do with fractional charges or confinement but it still needs to be solved.
 
As the difference occurs with different measurement methods and the significance is high, I don't think it is a problem with the individual measurements itself. It might be new physics, but I think the easiest explanation is a problem in theoretic calculations relating the measured values to a proton radius.
 

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