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We describe the design and performance of a large magnetic trap for storage and cooling of atomic hydrogen (H). The trap operates in the vacuum space of a dilution refrigerator at a temperature of 1.5 K. Aiming at a large volume of the trap, we implemented the octupole configuration of linear currents (Ioffe bars) for the radial confinement, combined with two axial pinch coils and a 3 T solenoid for the cryogenic H dissociator. The octupole magnet consists of eight race-track segments, which are compressed toward each other with magnetic forces. This provides a mechanically stable and robust construction with a possibility of replacement or repair of each segment. A maximum trap depth of 0.54 K (0.8 T) was reached, corresponding to an effective volume of 0.5 l for hydrogen gas at 50 mK. This is an order of magnitude larger than ever used for trapping atoms. [ABSTRACT FROM AUTHOR]

Precision spectroscopy of hydrogen often relies on effusive thermal atomic beams, and the uncertainty in the velocity distribution of these beams can introduce systematic errors and complicate lineshape models. Here, we present an apparatus capable of high signal-to-noise studies of these velocity distributions at cryogenic temperatures for both ground state (1S) and metastable (2S) hydrogen using a simple time-of-flight technique. We also investigate how the cryogenic nozzle geometry affects these results. [ABSTRACT FROM AUTHOR]

We present a measurement of the hydrogen 2S1/2-8D5/2 transition performed with a cryogenic atomic beam. The measured resonance frequency is ν=770649561570.9(2.0)  kHz, which corresponds to a relative uncertainty of 2.6×10-12. Combining our result with the most recent measurement of the 1S-2S transition, we find a proton radius of rp=0.8584(51) fm and a Rydberg constant of R∞=10973731.568332(52) m-1. This result has a combined 3.1σ disagreement with the Committee on Data for Science and Technology (CODATA) 2018 recommended value. [ABSTRACT FROM AUTHOR]

We report a new measurement of the n=2 Lamb shift in Muonium. Our result of 1047.2(2.3)stat(1.1)syst MHz comprises an order of magnitude improvement upon the previous best measurement. This value matches the theoretical calculation within 1 standard deviation allowing us to set limits on Lorentz and CPT violation in the muonic sector, as well as on new physics coupled to muons and electrons which could provide an explanation of the muon g-2 anomaly. [ABSTRACT FROM AUTHOR]