[ExI] proton measurement upset
thespike at satx.rr.com
Thu Jul 8 15:42:46 UTC 2010
Shrunken proton leaves scientists stunned
Thursday, 8 July 2010
Measurements with lasers have revealed that the proton may be a touch
smaller than predicted by current theories
PARIS: ... revised measurements shave 4% off the [proton]'s radius,
according to a study in Nature.
...if borne out in further experiments, the findings could challenge
fundamental precepts of quantum electrodynamics, the theory of how
quantum light and matter interact, said its authors.
A team of 32 international scientists led by Randolf Pohl of the Max
Planck Institute in Garching, Germany, had initially set out only to
confirm what was already known rather than overturn time-honoured
For decades, particle physicists have used the hydrogen atom as a
benchmark for measuring the size of protons, which are part of the core
of atoms. The advantage of hydrogen is its unrivalled simplicity: one
electron circles a single proton.
But this unit of measure turns out to have been wrong by a small but
critical margin, if the paper is right.
"We didn't imagine that there would be a gap between the known measures
of the proton and our own," admitted co-author Paul Indelicato, director
of the Kastler Brossel Laboratory at the Pierre and Marie Curie
University in Paris.
The new experiment - at least 10 times more accurate than any performed
to date - was envisioned by physicists 40 years ago, but only recent
developments in technology made it feasible.
The trick was to replace the electron in the hydrogen atom with a
negative muon, a particle with the same electric charge but more than
200 times heavier and unstable to boot.
The muon's larger mass gives muonic hydrogen a smaller atomic size and
allows a much larger interaction with the proton. As a result, the
proton's structure can be probed more accurately than by using hydrogen.
Jeff Flowers, a researcher at Britain's National Physical Laboratory in
Teddington, near London, said the work could take the theories of
particle physics into new territory.
If confirmed, it would do even more than the multi-billion-dollar giant
particle smasher at CERN in Switzerland to test the so-called Standard
Model, which sets down the notional list of sub-atomic particles, he
said in a commentary published in the same journal.
Either the previously accepted measures upon which hundreds of
calculations have been based are wrong, or there is a problem with the
theory of quantum electrodynamics itself.
Either way, physicists still have some serious explaining to do.
"Now the theoreticians are going to redo their equations, and more
experiments will be done to confirm or overturn it," said Indelicato.
"In two years we will do another experiment with the same equipment, but
this time with muonic helium," he added.
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