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Colloquium | Physics Colloquium | Physics Division

The Proton Size Determined from a New Measurement of the Atomic Hydrogen n=2 Lamb Shift: Resolving the Proton Radius Puzzle

PHY Colloquium

Abstract: A measurement almost a decade ago of the n=2 Lamb shift in muonic hydrogen allowed for a precise determination of the proton rms charge radius. This radius, however, showed a strong disagreement with radii determined from regular atomic hydrogen spectroscopy and electron scattering, and the disagreement has become known as the proton radius puzzle. We present a new high-precision measurement of the  atomic hydrogen n=2 Lamb shift. The measurement uses a new technique, frequency offset separated oscillatory fields (FOSOF), which is an innovation on the Ramsey technique. The measurement makes a precise determination of the proton charge radius, and this determination can be directly compared with the analogous determination using muonic hydrogen.

Our new program (EDMcubed) of determining the electron electric dipole moment using polar molecules embedded into solid argon will also be discussed.