This thesis describes a new measurement of the electron electric dipole moment
(eEDM, de) made using a pulsed beam of ytterbium fluoride (YbF) molecules. YbF
molecules are used as they greatly enhance the eEDM interaction with an applied
electric field. In addition they suppress interactions with magnetic fields in the plane
perpendicular to the applied electric field. This is hugely beneficial for suppressing the
systematic effect that limited previous atomic eEDM searches.
We measure the eEDM by performing a type of separated oscillating field interferometry,
wherein the direction of applied electric and magnetic fields are reversed in between pulses
of the molecular beam. From a dataset of 6194 individual eEDM measurements we find
de = (-2.4 ± 5.7stat ± 1.5syst) x 10[superscript -28] e cm. This result is consistent with zero, so we set
a new upper limit of |de| < 10.6 x 10[superscript -28] e cm at the 90% confidence level. A complete
analysis of the dataset is given, with a thorough account of all the supplementary tests
that were performed to check for systematic error.
After publishing this world leading result we proceeded to upgrade the experiment to
improve eEDM sensitivity and reduce certain systematic effects. This involved improving
the rf polarisation along the parallel plate transmission line, shortening the rf pulse
length and improving the magnetic shielding. A detailed discussion of the development
and testing of the upgrades is given, including new measurements of the systematic
uncertainties which will limit our next eEDM measurement.