Protons a bit smaller than thought. Scientists world over gasp aloud.


An article in Nature (a very prestigious refereed journal) announced on Wednesday that a team of researchers have measured the radius of a proton and found it to be 4% smaller than expected.

Now, for me speaking from an astronomical view point, this is a pretty great result. In Astronomy we’re often happy to get a measurement within a factor of 10 or so of what is predicted. But in elementary particle physics this small miss is a pretty big deal.

It could likely spell trouble for the Standard Model – which is the very successful description of interactions of the quarks and gluons that make up the internals of a proton. It’s such big trouble that the first instinct of many, including the editorial board of Nature, that the researchers messed up their calculation somehow.

But, as an article in the LA Times says:

“If the startling results are confirmed, a possibility that at least some physicists think is unlikely because the calculations involved are so difficult, they could have major ramifications for the so-called standard model on which most modern physics is based.

In an editorial accompanying the report in the journal Nature, physicist Jeff Flowers of the National Physical Laboratory in Teddington, England, said there were three possibilities: Either the experimenters have made a mistake, the calculations used in determining the size of the proton are wrong or, potentially most exciting and disturbing, the standard model has some kind of problem.

If the theory turns out to be wrong, ‘it would be quite revolutionary. It would mean that we know a lot less than we thought we knew,’ said physicist Peter J. Mohr of the National Institute of Standards and Technology in Gaithersburg, Md., who was not involved in the research. ‘If it is a fundamental problem, we don’t know what the consequences are yet.'”

Read the full article here.

More here.

Neat! Stay tuned… (as Steve Jobs is wont to say of late.)

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1 Comment

  1. Questions:
    (1) Since protons are made of quarks which I presume take up space in some sort of probability way as electrons do, is “size” easily discussed for these objects?
    (2) Is the Standard Model complete? Isn’t is missing stuff and such a finding could help guide the tweaks needed to get even better approximations?

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