From: scerir (scerir@libero.it)
Date: Sat Feb 10 2001 - 05:31:56 MST
http://PhysicsWeb.org/article/news/5/2/7
(with references, etc.)
The Standard Model describes how three of the four fundamental forces - the
strong, weak and electromagnetic forces, but not gravity - affect subatomic
particles. The anomalous results came from an experiment to determine how
much the 'spin' on a muon moves or 'precesses' when placed in a magnetic
field. The physicists injected an intense beam of muons into a powerful
magnetic field and measured the so-called g-2 ('g minus 2') value. The
g-factor of a particle relates its magnetic moment to its intrinsic angular
momentum or spin. The g-factor of both the muon and its lighter sibling, the
electron, are slightly larger than 2 due to various 'radiative corrections'.
Precise measurements of g-2 are powerful tests of theory.
The team found that the new value differed from the Standard Model by 2.6
standard deviations - in contrast with values previously obtained less
rigorous experiments that exactly matched the predictions of the theory. "We
are 99% sure that the present Standard Model calculations cannot describe
our data", said Gerry Bunce, project manager of the experiment.
The results can be interpreted in three ways. Firstly, the Standard Model is
fundamentally correct but need to be extended: the team could, for instance,
have glimpsed evidence of supersymmetry. This theory states that every
particle has a companion particle called its superpartner. "Many people
believe that the discovery of supersymmetry may be just around the corner",
said team member Lee Roberts, "We may have opened the first tiny window to
that world". Secondly, it is still statistically possible that the value is
consistent with theory. Thirdly, the model may be incomplete or entirely
wrong.
(Somebody - i.e. prof. Tullio Regge - is suggesting
that particles and dimensions are ...... infinite)
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