Because of hydrogen’s simplicity, its energy levels are well-described by quantum electrodynamics (QED). This had made precision spectroscopy of hydrogen a favorite testbed for bound-stated QED. In addition, assuming the QED calculations are correct, one can use hydrogen spectroscopy to determine the Rydberg constant and the proton-charge radius. Any discrepancy of these constants determined in different systems can indicate new physics. In 2010, such a discrepancy was found [Pohl, R. et al. Nature 466, 213 (2010)] when the proton charge radius in muonic hydrogen was found to be about 5-sigma away from the value found through normal hydrogen spectroscopy (termed the proton-radius puzzle). In this talk, I will discuss our ongoing experiments at Colorado State University to produce additional spectroscopic hydrogen data to address this puzzle. Specifically, we have been measuring the 2S-8D transition in a cryogenic beam of hydrogen, which we hope will provide a new determination of the proton charge radius soon. In addition, I will discuss our efforts at laser slowing our atomic hydrogen beam, which could allow for more precise spectroscopy in the future.

Bio: Dylan Yost grew up in Colorado and obtained his BS in Engineering Physics from the Colorado School of Mines in 2005. While at Mines, he performed undergraduate research with Prof. Durfee and Prof. Ohno. He received his PhD on work with vacuum-ultraviolet frequency combs from the University of Colorado in 2011. In 2012, he was a Humboldt Fellow at the Max Planck Institute for Quantum Optics and worked on precision hydrogen spectroscopy. He is currently an associate professor at Colorado State University. He has received an NSF CAREER award and the NIST Precision Measurement Grant for his hydrogen spectroscopy experiments.