The electron is predicted to be slightly aspheric [1], with a distorsion characterised by the electric dipole moment (EDM), d e . No experiment has ever detected this deviation. The standard model of particle physics predicts that d e is far too small to detect [2], 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 d e that should be detectable [3]. 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 is difficult to reconcile with the absence of an electron EDM at the present limit of sensitivity [4,2]. The size of the EDM is also intimately related to one 1

The most sensitive measurements of the electron electric dipole moment de have previously been made using heavy atoms. Heavy polar molecules offer a greater sensitivity to de because the interaction energy to be measured is typically 10 3 times larger than in a heavy atom. We report the first measurement of this kind, for which we have used the molecule YbF. Together, the large interaction energy and the strong tensor polarizability of the molecule make our experiment essentially free of the systematic errors that currently limit de measurements in atoms. Our first result de = (−0.2 ± 3.2) × 10 −26 e cm is less sensitive than the best atom measurement, but is limited only by counting statistics and demonstrates the power of the method.

We demonstrate slowing and longitudinal cooling of a supersonic beam of CaF molecules using counter-propagating laser light resonant with a closed rotational and almost closed vibrational transition. A group of molecules are decelerated by about 20 m/s by applying light of a fixed frequency for 1.8 ms. Their velocity spread is reduced, corresponding to a final temperature of about 300 mK. The velocity is further reduced by chirping the frequency of the light to keep it in resonance as the molecules slow down.Comment: 6 pages, 6 figure

We have decelerated a supersonic beam of 174YbF molecules using a switched sequence of electrostatic field gradients. These molecules are 7 times heavier than any previously decelerated. An alternating gradient structure allows us to decelerate and focus the molecules in their ground state. We show that the decelerator exhibits the axial and transverse stability required to bring the molecules to rest. Our work significantly extends the range of molecules amenable to this powerful method of cooling and trapping.

We propose an experiment to measure the electric dipole moment (EDM) of the electron using ultracold YbF molecules. The molecules are produced as a thermal beam by a cryogenic buffer gas source, and brought to rest in an optical molasses that cools them to the Doppler limit or below. The molecular cloud is then thrown upward to form a fountain in which the EDM of the electron is measured. A non-zero result would be unambiguous proof of new elementary particle interactions, beyond the standard model. 14 Appendix. Further discussion of excitation by the molasses lasers 14 References 15 2 These eight calculations give the effective electric field along the internuclear axis of the YbF molecule as (3.1,1.9,2.6,2.6,2.5,2.5,2.3,2.4) TV m −1 respectively (after correcting a trivial factor of two error in Quiney et al). We take the value to be 2.5 TV m −1 . With the molecule in a 1 MV m −1 external field, the projection of the internuclear axis onto the external field reduces this to 1.4 TV m −1 . The 7.2 GV m −1 effective field in the Tl experiment [13] was 200 times smaller. New Journal of Physics 15 (2013) 053034 (http://www.njp.org/)

We recently reported a new measurement of the electron's electric dipole moment using YbF molecules (Hudson et al 2011 Nature 473 493).Here, we give a more detailed description of the methods used to make this measurement, along with a fuller analysis of the data. We show how our methods isolate the electric dipole moment from imperfections in the experiment that might mimic it. We describe the systematic errors that we discovered, and the small corrections that we made to account for these. By making a set of additional measurements with greatly exaggerated experimental imperfections, we find upper bounds on possible uncorrected systematic errors which we use to determine the systematic uncertainty in the measurement. We also calculate the size of some systematic effects that have been important in previous electric dipole moment measurements, such as the motional magnetic field effect and the geometric phase, and show them to be negligibly small in the present experiment. Our result is consistent with an electric dipole moment of zero, so we provide upper bounds to its size at various confidence levels. Finally, we review the prospects for future improvements in the precision of the experiment.

Heavy polar molecules can be used to measure the electric dipole moment of the electron, which is a sensitive probe of physics beyond the Standard Model. The value is determined by measuring the precession of the molecule's spin in a plane perpendicular to an applied electric field. The longer this precession evolves coherently, the higher the precision of the measurement. For molecules in a trap, this coherence time could be very long indeed. We evaluate the sensitivity of an experiment where neutral molecules are trapped electrically, and compare this to an equivalent measurement in a molecular beam. We consider the use of a Stark decelerator to load the trap from a supersonic source, and calculate the deceleration efficiency for YbF molecules in both strong-field seeking and weak-field seeking states. With a 1 s holding time in the trap, the statistical sensitivity could be ten times higher than it is in the beam experiment, and this could improve by a further factor of five if the trap can be loaded from a source of larger emittance. We study some effects due to field inhomogeneity in the trap and find that rotation of the electric field direction, leading to an inhomogeneous geometric phase shift, is the primary obstacle to a sensitive trap-based measurement.

We have developed a pulsed supersonic beam of slow, cold YbF molecular radicals with an intensity of 1.4 × 109 YbF molecules per steradian per pulse in the X2 Σ+ (v = 0, N = 0) ground state. The translational and rotational temperatures of the beam are equal. The lowest temperature produced was 1.4 K and the slowest centre-of-mass velocity was 290 K. We show that YbF can be made either by ablating Yb metal into a fluorine-bearing carrier gas or by ablating solid precursors into a pure inert carrier gas. This source is suitable for injecting a molecule decelerator and for high-resolution laser-rf-double-resonance studies such as the measurement of the electron electric dipole moment.