# Particle Physics Seminar

## Wednesday 26^{th} October 2011 at 1:30pm

Poynting Small Lecture Theatre

*(tea, coffee and biscuits served at 1:15pm)*
# Improved Measurement of the Electron EDM

## Ed Hinds (Imperial College)

**Abstract**

The electron's charge distribution can be characterised by its
electric dipole moment (EDM), which measures the deviation
of its electric interactions from purely spherical. According to the
standard model, this EDM is some eleven orders of magnitude
below the current experimental limit. However, most extensions to the
standard model predict much larger values, potentially accessible to
measurement. Hence, the search for the electron EDM is a search
for physics beyond the standard model. Moreover, a non-zero EDM
breaks time-reversal symmetry which, in many models of particle
physics, is equivalent to breaking the symmetry between matter and
antimatter, known as CP symmetry. New CP-breaking physics is thought
to be needed to explain the existence of a material universe. We
have used a supersonic beam of cold YbF molecules to measure the
electron EDM, obtaining the result a new upper limit
with 90% confidence. Our result, consistent with zero,
indicates that the electron is spherical at this improved level of
precision. Our measurement, of atto-eV energy shifts in a molecule,
probes new physics at the tera-eV energy scale. Many extensions to
the standard model, such as the minimal supersymmetric standard
model, naturally predict large EDMs and our measurement places
significant constraints on the parameters of these theories.