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发帖数: 6421 | 1 【 以下文字转载自 Physics 讨论区 】
发信人: xiumu (朽木☀江湖夜雨十年灯), 信区: Physics
标 题: Improved measurement of the shape of the electron
发信站: BBS 未名空间站 (Wed May 25 14:38:59 2011, 美东)
Improved measurement of the shape of the electron
J. J. Hudson, D. M. Kara, I. J. Smallman, B. E. Sauer, M. R.
Tarbutt & E. A. Hinds
AffiliationsContributionsCorresponding author
Nature 473, 493–496 (26 May 2011) doi:10.1038/nature10104
Received 18 February 2011 Accepted 08 April 2011 Published online 25 May
2011
The electron is predicted to be slightly aspheric1, with a distortion
characterized by the electric dipole
moment (EDM), de. No experiment has ever detected this deviation. The
standard model of particle physics
predicts that de is far too small to detect2, being some eleven orders of
magnitude smaller than the current
experimental sensitivity. However, many extensions to the standard model
naturally predict much larger
values of de that should be detectable3. This makes the search for the
electron EDM a powerful way to search
for new physics and constrain the possible extensions. In particular, the
popular idea that new
supersymmetric particles may exist at masses of a few hundred GeV/c2 (where
c is the speed of light) is
difficult to reconcile with the absence of an electron EDM at the present
limit of sensitivity2, 4. The size of the
EDM is also intimately related to the question of why the Universe has so
little antimatter. If the reason is that
some undiscovered particle interaction5 breaks the symmetry between matter
and antimatter, this should
result in a measurable EDM in most models of particle physics2. Here we use
cold polar molecules to measure
the electron EDM at the highest level of precision reported so far,
providing a constraint on any possible new
interactions. We obtain de = (−2.4 ± 5.7stat ±&#
8201;1.5syst) × 10−28e cm, where e is the charge on
the electron,
which sets a new upper limit of |de| < 10.5 × 10&#
8722;28e cm with 90 per cent confidence. This result, consistent
with zero, indicates that the electron is spherical at this improved level
of precision. Our measurement of
atto-electronvolt energy shifts in a molecule probes new physics at the tera
-electronvolt energy scale2. |
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