G. Gabrielse

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.

Open-endcap Penning traps for high precision experiments

Abstract Cylindrical Penning traps with open-endcap electrodes are compared with the hyperbolic traps which are currently used for high precision experiments. Cylindrical traps are easier to construct and allow free access to the center of the trap for particle loading, laser beams, or microwaves. The trapping potential can be tuned while particles are inside the trap to improve harmonicity. Special geometries are noted which allow anharmonicities to be tuned out without affecting the trap well depth, and the effects of trap imperfections and gaps between the electrodes are discussed. Such traps will be used for measuring the antiproton mass, for colling of trapped antiprotons, and possibly for producing antihydrogen.

Antihydrogen production using trapped plasmas

Abstract Now that antiprotons have been captured in an ion trap, we investigate the possibility of producing antihydrogen by merging cold trapped plasmas of antiprotons and positrons. The calculated rate for antihydrogen production by the three-body recombination p − + e + + e + → H + e + is many orders of magnitude higher than for any other proposed technique, opening up intriguing experimental possibilities.

Measurement of the Stokes parameters of light

We describe a measuring system for determining the state of polarization of a beam of light in terms of its Stokes parameters. The technique which can be fully automated incorporates a monochromator and single photon counting detection and can thus be applied over a large wavelength range for very weak optical signals. Fourier transformation of the data by an on-line minicomputer allows immediate calculation of the Stokes parameters. We discuss special applications to light emitted from excited atomic systems with and without cylindrical symmetry.

Cylindrical Penning traps with orthogonalized anharmonicity compensation

Abstract Compensated Penning traps with cylindrical ring and compensation electrodes and flat endcaps are considered as alternatives to high precision traps with hyperbolic ring and endcap electrodes. Cylindrical and flat electrodes can be more easily and precisely constructed, especially for the very small traps which are desirable for ion trapping. They are easily studied since Laplaces equation can be solved by a series expansion which is discussed in most electricity and magnetism textbooks. A central new result is that a judicious choice of the height-to-diameter ratio for a cylindrical trap makes the axial oscillation frequency of a trapped particle independent of adjustments in the compensation potential, just as has been recently proposed for hyperbolic traps. Other properties of such orthogonalized cylindrical traps appear to be adequate for particle trapping so that properly designed cylindrical traps are promising alternatives for high precision work, ready for laboratory testing. Whether or not cylindrical traps will be able to replace hyperbolic traps entirely for the highest precision work, a major point of this paper is that orthogonalized traps can be built with any reasonable electrode geometry. Special access traps with orthogonalized anharmonicity compensation are thus completely feasible, though numerical calculations will be generally required for their design.

Cavity Control of a Single-Electron Quantum Cyclotron: Measuring the Electron Magnetic Moment

Measurements with a one-electron quantum cyclotron determine the electron magnetic moment, given by

Search for the electric dipole moment of the electron with thorium monoxide

g/2 = 1.001\,159\,652\,180\,73\,(28)\,[0.28~\textrm{ppt}]

Self‐shielding superconducting solenoid systems

, and the fine structure constant,

First positron cooling of antiprotons.

\alpha^{-1}=137.035\,999\,084\,(51)\,[0.37~\textrm{ppb}]

Trapped antihydrogen for spectroscopy and gravitation studies: Is it possible?

. Brief announcements of these measurements are supplemented here with a more complete description of the one-electron quantum cyclotron and the new measurement methods, a discussion of the cavity control of the radiation field, a summary of the analysis of the measurements, and a fuller discussion of the uncertainties.