Proton Radius Puzzle:

Discussion in 'General Science & Technology' started by paddoboy, Aug 12, 2016.

  1. paddoboy Valued Senior Member

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    New measurement with deuterium nucleus confirms proton radius puzzle is real
    August 12, 2016 by Bob Yirka report

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    The quark structure of the proton. There are two up quarks in it and one down quark. The strong force is mediated by gluons (wavey). The strong force has three types of charges, the so-called red, green and the blue. Note that the choice of green for the down quark is arbitrary; the "color charge" is thought of as circulating among the three quarks. Credit: Arpad Horvath/Wikipedia

    A large team made up of researchers from across the globe has repeated experiments conducted several years ago that showed a different radius for a proton when it was orbited by a muon as opposed to an electron

    Scientists have been able to calculate the radius of a proton (0.88 ± 0.01 femtometers) for some time using the charge of the electron that orbits around it and doing so has helped confirm theories regarding the Standard Model. But, in trying to improve the accuracy of the measurement by using a negatively charged muon (which orbits closer to the proton), researchers at the Max Planck Institute back in 2010 found a different radius—one that was 7 deviations from what was considered the official value. This proton radius puzzle has had physicists scratching their heads ever since because it suggests there is an error in the Standard Model somewhere.

    Read more at: http://phys.org/news/2016-08-deuterium-nucleus-proton-radius-puzzle.html#jCp
     
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  3. paddoboy Valued Senior Member

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    More information: R. Pohl et al, Laser spectroscopy of muonic deuterium, Science (2016). DOI: 10.1126/science.aaf2468


    Abstract

    The deuteron is the simplest compound nucleus, composed of one proton and one neutron. Deuteron properties such as the root-mean-square charge radius rd and the polarizability serve as important benchmarks for understanding the nuclear forces and structure. Muonic deuterium μd is the exotic atom formed by a deuteron and a negative muon μ–. We measured three 2S-2P transitions in μd and obtain rd = 2.12562(78) fm, which is 2.7 times more accurate but 7.5σ smaller than the CODATA-2010 value rd = 2.1424(21) fm. The μd value is also 3.5σ smaller than the rd value from electronic deuterium spectroscopy. The smaller rd, when combined with the electronic isotope shift, yields a "small" proton radius rp, similar to the one from muonic hydrogen, amplifying the proton radius puzzle.



    Read more at: http://phys.org/news/2016-08-deuterium-nucleus-proton-radius-puzzle.html#jCp
     
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  5. Daecon Kiwi fruit Valued Senior Member

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    So I guess the muon isn't "compressing" the proton somehow?
     
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