Proton charge radius calculation

In summary, the conversation discusses an experiment involving a muon and a proton to calculate the proton charge radius. The measured muonic hydrogen transition disagrees with predictions based on the proton radius from hydrogen spectroscopy and electron-proton scattering experiments. This discrepancy is attributed to the sensitivity of the energy levels to the proton's properties. The cause of this disagreement is still unknown and is being discussed in a separate thread and referenced paper.
  • #1
edguy99
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In this link the proton charge radius is calculated based on an experiment involving a muon and a proton http://www.sps.ch/en/artikel/progresses/muonic_hydrogen_and_the_proton_radius_puzzle_20/

It talks about "In summary, we have measured the muonic hydrogen transition at a frequency of 49881.88(76) GHz which corresponds to an energy of 206.2949(32) meV [1]. The position of this line strongly disagrees with predictions (shown by the orange points in Fig. 3) which have been computed assuming the proton radius extracted from hydrogen spectroscopy and theory, and the proton radius from electron-proton scattering experiments."

Is this disagreement unique to muonic atoms or is there also disagreement from theory for a normal electron/proton atom?
 
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  • #2
edguy99, Since the muon is 200 times heavier than the electron, the Bohr radius for a muonic hydrogen atom is 200 times smaller. Thus the energy levels of the lowest states are much more sensitive to the properties of the proton, and in particular are affected by its charge radius. The apparent discrepancy he talks about is not yet understood.
 
  • #3
I raised a discussion of an aspect of this result in an earlier thread:

https://www.physicsforums.com/showthread.php?t=435990

There, the following reference was presented as explaining the finding:

http://arxiv.org/abs/1010.3421

[Edit: I notice this paper has undergone significant revision since its first preprint version and final published form. It is now less clear in its conclusions.]
 
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1. What is the proton charge radius and why is it important?

The proton charge radius is a measure of the size of the proton, which is one of the fundamental particles that make up atoms. It is important because it helps us understand the structure and behavior of atoms, which are the building blocks of all matter in the universe.

2. How is the proton charge radius calculated?

The proton charge radius is calculated using a technique called electron scattering. This involves shooting high-energy electrons at protons and measuring how they interact. This data is then used to calculate the proton charge radius.

3. What is the current accepted value for the proton charge radius?

The current accepted value for the proton charge radius is 0.8775 femtometers (fm). However, there is ongoing research and debate in the scientific community about the precise value, with some recent studies suggesting a slightly larger radius.

4. How has the calculation of the proton charge radius evolved over time?

The calculation of the proton charge radius has evolved over time as new techniques and technologies have become available. Early methods involved using atomic spectroscopy and X-ray scattering, while more recent methods involve precision measurements using high-energy accelerators.

5. Why is there controversy surrounding the proton charge radius calculation?

The controversy surrounding the proton charge radius calculation stems from discrepancies between different experimental results and theoretical predictions. This has led to ongoing debates and efforts to refine and improve the accuracy of the calculation. Additionally, recent research has suggested that the proton charge radius may be slightly larger than previously thought, which has sparked further discussion and investigation.

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