Abstract
Precise determinations of transition frequencies of simple atomic systems are required for a number of fundamental applications such as tests of quantum electrodynamics (QED), the determination of fundamental constants and nuclear charge radii. The sharpest transition in atomic hydrogen occurs between the metastable 2S state and the 1S ground state. Its transition frequency has now been measured with almost 15 digits accuracy using an optical frequency comb and a cesium atomic clock as a reference [1]. A recent measurement of the 2S – 2P3/2 transition frequency in muonic hydrogen is in significant contradiction to the hydrogen data if QED calculations are assumed to be correct [2, 3]. We hope to contribute to this so-called "proton size puzzle" by providing additional experimental input from hydrogen spectroscopy.
Highlights
Atomic hydrogen has been the Rosetta Stone for quantum physics
Precise determinations of transition frequencies of simple atomic systems are required for a number of fundamental applications such as tests of quantum electrodynamics (QED), the determination of fundamental constants and nuclear charge radii
A recent measurement of the 2S − 2P3/2 transition frequency in muonic hydrogen is in significant contradiction to the hydrogen data if QED calculations are assumed to be correct [2, 3]
Summary
Atomic hydrogen has been the Rosetta Stone for quantum physics. Through the successive refinement of its theoretical description, starting from the phenomenological description of J.J Balmer, it provided a concise argument for the wave nature of matter. The measurement of transition frequencies in muonic hydrogen provides a much more sensitive method to determine the proton charge radius compared to regular hydrogen. 2. Determining the Parameters The theoretical description of the hydrogen energy levels uses four parameters: The fine structure constant α, the electron to proton mass ratio me/mp, the proton charge radius rp and the Rydberg constant R∞.
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