Hessels, EricBezginov, Nikita2020-08-112020-08-112020-032020-08-11http://hdl.handle.net/10315/37734A high-precision measurement of the transition frequency between the 2S_1/2, f=0 and 2P_1/2, f=1 states in atomic hydrogen is presented. The interval is measured by using a fast beam of hydrogen atoms and a novel method of frequency-offset separated oscillatory fields (FOSOF), an extension of the separated-oscillatory-fields (SOF) method. Our result for the 2S_1/2, f=0-to-2P_1/2, f=1 interval is 909871.7 kHz with the total uncertainty of 3.2 kHz, which is the most precise measurement of this transition to date. The root-mean-squared charge radius of the proton, determined from this measurement, is r_p=0.833(10) fm, in agreement with the proton radius determined from muonic-hydrogen spectroscopy, and 4.2 standard deviations away from the CODATA 2014 recommended value, which is determined entirely using electrons (using hydrogen spectroscopy and electron-proton scattering).Author owns copyright, except where explicitly noted. Please contact the author directly with licensing requests.PhysicsElectronic Thesis or Dissertation2020-08-11ProtonProton radiusProton sizeHydrogenHydrogen spectroscopySpectroscopyPrecision spectroscopyProton rms charge radiusProton radius puzzleLamb shiftFOSOFSOF