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posted by mrpg on Sunday October 08 2017, @05:38AM   Printer-friendly
from the small-but-important dept.

Submitted via IRC for Bytram

The proton might truly be smaller than was thought. Experiments on an exotic form of hydrogen first found a puzzling discrepancy with the accepted size in 2010. Now, evidence from a German and Russian team points to a smaller value for the size of the proton with ordinary hydrogen, too.

The results, which appeared on 5 October in Science, could be the first step towards resolving a puzzle that has made physicists doubt their most precise measurements, and even their most cherished theories.

[...] Pohl's team found the proton to be 4% smaller than the accepted value. Some researchers speculated that perhaps some previously unknown physics could make muons act differently than electrons. This would have required a revision of the standard model of particle physics, which predicts that muons and electrons should be identical in every way except for their masses — and might have pointed to the existence of yet-to-be-discovered elementary particles.

[...] But the German–Russian group is not quite ready to claim that the puzzle has been solved, Maisenbacher says. "We have not identified any conclusive reason why the other measurements should not be correct themselves," he says. "We would like to see more experiments from other people."

Source: Proton-size puzzle deepens


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  • (Score: 2) by https on Sunday October 08 2017, @07:01AM (6 children)

    by https (5248) on Sunday October 08 2017, @07:01AM (#578807) Journal

    Given that

    The heavier [ muon ] spends more time inside the nucleus, which means that the proton’s size has a much larger effect on the muon’s energies — which, in turn, should lead to a much more precise estimate of the proton’s radius.

    ...and all interactions are two way, wouldn't it be possible that a muon affects a nucleus more than an electron does?

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  • (Score: 3, Interesting) by maxwell demon on Sunday October 08 2017, @11:54AM (5 children)

    by maxwell demon (1608) on Sunday October 08 2017, @11:54AM (#578854) Journal

    I'm not a nuclear physicist, but more concentration of negative charge in the proton indeed sounds like it should reduce the proton's radius. However I would guess that someone already considered that possibility and found it not sufficient to explain the discrepancy.

    --
    The Tao of math: The numbers you can count are not the real numbers.
    • (Score: 2) by opinionated_science on Sunday October 08 2017, @06:16PM (4 children)

      by opinionated_science (4031) on Sunday October 08 2017, @06:16PM (#578922)

      neither am I , but I am a molecule meddler. It is curious to see what new theory may come out of this, as muon-catalysed fusion was demonstrated some years ago, and gives an interesting view on possible natural processes.

      i.e. the most common method may be A but nature has billions of years may also use B,C...etc...

      An interesting side-point about the size of the proton is biological systems that count on protons be the right size due to the pore size (proton pumps are *really* specific - deuterium doesn't work...)

      • (Score: 0) by Anonymous Coward on Sunday October 08 2017, @08:04PM

        by Anonymous Coward on Sunday October 08 2017, @08:04PM (#578952)

        An interesting side-point about the size of the proton is biological systems that count on protons be the right size due to the pore size (proton pumps are *really* specific - deuterium doesn't work...)

        That sounds wrong to me. A quick search found this:

        D+ was able to permeate proton channels, but with a conductance only about 50% that of H+

        https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2219434/ [nih.gov]

      • (Score: 0) by Anonymous Coward on Sunday October 08 2017, @08:51PM

        by Anonymous Coward on Sunday October 08 2017, @08:51PM (#578971)

        Here is another one: https://www.ncbi.nlm.nih.gov/pubmed/18371493 [nih.gov]

        In table 1 they show different steps are 2x and 5x faster using hydrogen, but still occurring using deuterium.

      • (Score: 2) by maxwell demon on Monday October 09 2017, @07:12AM (1 child)

        by maxwell demon (1608) on Monday October 09 2017, @07:12AM (#579169) Journal

        The size of the proton doesn't matter in that; for anything molecular it's effectively point-sized. The reason why Deuterium behaves differently is that it has double the mass.

        Note that while the common wisdom is that the chemical properties of isotopes are identical, this is not completely true for hydrogen/deuterium, exactly because of the large relative mass difference.

        --
        The Tao of math: The numbers you can count are not the real numbers.