Tests of fundamental physics using precision measurements of simple atomic systems

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The proposed research involves several separate areas, each with very different methodologies and objectives. All areas are high-profile, and Dr. Hessels is considered by the international atomic physics community to be a leader in these areas:1. Lamb shift and the proton charge radius The atomic hydrogen n=2 Lamb shift is being measured using microwaves and the new Frequency-Offset Separated-Oscillatory-Fields (FOSOF) technique developed in Dr. Hessels' group. When the measurement is completed, it will determine the charge radius of the proton at a higher precision than can be achieved from all other existing hydrogen measurements combined. This result will help to resolve (or enhance) the current several-standard-deviation discrepancy between different determinations of the charge radius. This discrepancy is referred to by the community as the proton radius puzzle, and has been the topic of hundreds of papers in the past 7 years.2. Helium fine structure and the fine-structure constant New ultraprecise microwave FOSOF measurements of the n=2 triplet P fine structure of helium are being completed, and will be the most precise measurements of any helium fine structure. They will form a new precise test of quantum electrodynamics and will also move the precision measurements community closer to a high-precision determination of the fine-structure constant (the fundamental constant of nature that determines the strength of all electromagnetic interactions). A comparison between this determination of the fine-structure constant and a determination from the electron g-factor forms a strong test of the theories of physics (including possible effects of dark matter or other physics beyond the Standard Model). 3. Trapping, laser-cooling and precise spectroscopy of antimatter atoms Dr. Hessels and the ATRAP collaboration are preparing for an experiment in which trapped antihydrogen atoms will interact with laser light. The laser light will be used to slow the motion of the antimatter atoms, and this slowing is the next major step towards precision spectroscopy of these anti-atoms. A comparison between hydrogen and antihydrogen spectroscopy will test CPT and the symmetry between matter and antimatter. Successful laser cooling and spectroscopy of laser-cooled antimatter will greatly advance the field of antimatter research.4. Other workAdditionally, Dr. Hessels is working with the ATRAP collaboration on a more precise measurement of the antiproton magnetic moment, is collaborating with Dr. Horbatsch (York) on calculations of the effect of quantum interference on precision measurements, is collaborating with Dr. Storry (York) on precision spectroscopy of positronium and on the production of a new positronic atom (composed of a negative hydrogen ion and a positron), and is collaborating with Dr. Vutha (U. Toronto) on a new idea for measuring the electric dipole moment of the electron.