By trapping a single electron in an isolated chamber cooled to near absolute
zero, physicists were able to measure the particle's magnetic moment - a key
quantum property - at a precision of 1.3 parts in 10 trillion.
A new assessment of the electron is the most precise measurement of a
particle ever taken, at a precision of 1.3 parts in 10 trillion, and could
tell us about new physics happening at the smallest scales.
The electron’s magnetic moment is a quantum property related to magnetism
and is predicted by the standard model, our current understanding of how the
basic building blocks of the universe interact. But the standard model is
unable to explain certain real-world observations, like dark matter or the
absence of antimatter, so researchers are seeking discrepancies between
predicted and measured properties of fundamental particles to look for new
physics.
So far, measurements of the electron’s magnetic moment have agreed with the
standard model, but only to a certain level of precision. Now, Gerald
Gabrielse at Northwestern University in Illinois and his colleagues have
measured the property 2.2 times more precisely than ever before, finding it
in agreement with the previous best measurement, in 2008.
To do this, Gabrielse and his team trapped a single electron in a chamber
with an ultra-stable magnetic and electric field, isolated from any external
forces and cooled to just above absolute zero, and then measured the
electron’s response as they changed the magnetic field.
“This new measurement boasts the most precise measurement of a physical
property of a fundamental particle ever, and therefore stands as the gold
standard for precision measurements testing physicists’ current best theory
of all the universe’s known particles and forces,” says Alex Keshavarzi at
the University of Manchester, UK, who wasn’t involved in the research.
While this new measurement agrees with the standard model, as the old one
did, it can’t be used to fully test the theory because its predictions are
actually less precise than the measurement. This is because the standard
model relies on a number called the fine structure constant, a measure of
the strength of electromagnetism between particles. Physicists can’t quite
agree on the size of this constant, with two groups finding significantly
different values for it.
With a more precise and accurate fine structure constant, it should be
possible to properly compare the new electron magnetic moment value with
that predicted by the standard model. If at that point there is a
discrepancy between the two, then new physics will be needed to explain it,
such as a new structure for the electron, which is currently thought to be
point-like and structureless.
Reference: arxiv.org/abs/2209.13084
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Physics