Adam West

Order of Magnitude Smaller Limit on the Electric Dipole Moment of the Electron

Stubbornly Spherical The shape of the electrons charge distribution reflects the degree to which switching the direction of time impacts the basic ingredients of the universe. The Standard Model (SM) of particle physics predicts a very slight asphericity of the charge distribution, whereas SM extensions such as supersymmetry posit bigger and potentially measurable, but still tiny, deviations from a perfect sphere. Polar molecules have been identified as ideal settings for measuring this asymmetry, which should be reflected in a finite electric dipole moment (EDM) because of the extremely large effective electric fields that act on an electron inside such molecules. Using electron spin precession in the molecule ThO, Baron et al. (p. 269, published online 19 December; see the cover; see the Perspective by Brown) measured the EDM of the electron as consistent with zero. This excludes some of the extensions to the SM and sets a bound to the search for a nonzero EDM in other facilities, such as the Large Hadron Collider. Spin precession measurements in the polar molecule thorium monoxide indicate a nearly spherical charge distribution of an electron. [Also see Perspective by Brown] The Standard Model of particle physics is known to be incomplete. Extensions to the Standard Model, such as weak-scale supersymmetry, posit the existence of new particles and interactions that are asymmetric under time reversal (T) and nearly always predict a small yet potentially measurable electron electric dipole moment (EDM), de, in the range of 10−27 to 10−30 e·cm. The EDM is an asymmetric charge distribution along the electron spin (S→) that is also asymmetric under T. Using the polar molecule thorium monoxide, we measured de = (–2.1 ± 3.7stat ± 2.5syst) × 10−29 e·cm. This corresponds to an upper limit of | de | < 8.7 × 10−29 e·cm with 90% confidence, an order of magnitude improvement in sensitivity relative to the previous best limit. Our result constrains T-violating physics at the TeV energy scale.

Methods, Analysis, and the Treatment of Systematic Errors for the Electron Electric Dipole Moment Search in Thorium Monoxide

We recently set a new limit on the electric dipole moment of the electron (eEDM) (J Baron et al and ACME collaboration 2014 Science 343 269–272), which represented an order-of-magnitude improvement on the previous limit and placed more stringent constraints on many charge-parity-violating extensions to the standard model. In this paper we discuss the measurement in detail. The experimental method and associated apparatus are described, together with the techniques used to isolate the eEDM signal. In particular, we detail the way experimental switches were used to suppress effects that can mimic the signal of interest. The methods used to search for systematic errors, and models explaining observed systematic errors, are also described. We briefly discuss possible improvements to the experiment.

STIRAP preparation of a coherent superposition of ThO

Experimental searches for the electron electric dipole moment (EDM) probe new physics beyond the Standard Model. The current best EDM limit was set by the ACME Collaboration [Science \textbf{343}, 269 (2014)], constraining time reversal symmetry (

H^3\Delta_1

T

states for an improved electron EDM measurement

) violating physics at the TeV energy scale. ACME used optical pumping to prepare a coherent superposition of ThO

An Underappreciated Radiation Hazard from High Voltage Electrodes in Vacuum

H^3\Delta_1

Improved Thermochemical Beam Source of ThO for Measuring the Electric Dipole Moment of the Electron

states that have aligned electron spins. Spin precession due to the molecules internal electric field was measured to extract the EDM. We report here on an improved method for preparing this spin-aligned state of the electron by using STIRAP. We demonstrate a transfer efficiency of

Rotation Sensing with a Trapped Barium Ion

75\pm5\%

Prospects for a Third Generation ACME Search for an Electron Electric Dipole Moment

, representing a significant gain in signal for a next generation EDM experiment. We discuss the particularities of implementing STIRAP in systems such as ours, where molecular ensembles with large phase-space distributions are transfered via weak molecular transitions with limited laser power and limited optical access.

Characterization and Suppression of Systematic Errors in the ACME II Measurement of the Electron Electric Dipole Moment

Abstract The use of high voltage (HV) electrodes in vacuum is commonplace in physics laboratories. In such systems, it has long been known that electron emission from an HV cathode can lead to bremsstrahlung x rays; indeed, this is the basic principle behind the operation of standard x-ray sources. However, in laboratory setups where x-ray production is not the goal and no electron source is deliberately introduced, field-emitted electrons accelerated by HV can produce x rays as an unintended hazardous byproduct. Both the level of hazard and the safe operating regimes for HV vacuum electrode systems are not widely appreciated, at least in university laboratories. A reinforced awareness of the radiation hazards associated with vacuum HV setups would be beneficial. The authors present a case study of a HV vacuum electrode device operated in a university atomic physics laboratory. They describe the characterization of the observed x-ray radiation, its relation to the observed leakage current in the device, the steps taken to contain and mitigate the radiation hazard, and suggested safety guidelines.