Robert F. C. Vessot

Limit on Lorentz and CPT violation of the proton using a hydrogen maser

We present a new measurement constraining Lorentz and

Measurement of the Unperturbed Hydrogen Hyperfine Transition Frequency

\mathrm{CPT}

Testing CPT and Lorentz symmetry with hydrogen masers

violation of the proton using a hydrogen maser double resonance technique. A search for hydrogen Zeeman frequency variations with a period of the sidereal day (23.93 h) sets a limit on violation of Lorentz and

The atomic hydrogen maser oscillator

\mathrm{CPT}

A Method for Eliminating the Wall Shift in the Atomic Hydrogen Maser

symmetry of the proton at the

New clock comparison searches for Lorentz and CPT violation

{10}^{\ensuremath{-}27}

A hydrogen maser at temperatures below 1 K

GeV level, independent of nuclear model uncertainty, which improves significantly on previous bounds.

High accuracy time and frequency from space

The results of a joint experiment aimed primarily at the determination of the frequency of the H1 hyperfine transition (F = 1, mF = 0) ? (F = 0, mF = 0) is reported. In terms of the frequency of the Cs133 hyperfine transition (F = 4, mF = 0) ?(F = 3, mF = 0), defined as 9192 631 770 Hz, for the unperturbed hydrogen transition frequency the value ?H = 1420 405 751.768 Hz is obtained. This result is the mean of two independent evaluations against the same cesium reference, which differ by 2 × 10-3 Hz. We estimate the one-sigma uncertainty of the value ?H also to be 2 × 10-3 Hz. One evaluation is based on wall-shift experiments at Harvard University; the other is a result of a new wall-shift measurement using many storage bulbs of different sizes at the National Bureau of Standards. The experimental procedures and the applied corrections are described. Results for the wall shift and for the frequency of hydrogen are compared with previously published values, and error limits of the experiments are discussed.

The Cold Hydrogen Maser

In a recent paper [Phys. Rev. D 63, 111101 (2001)] we reported a new limit on CPT (charge, parity, and time reversal) and Lorentz violation of the proton by using a hydrogen maser to search for a sidereal variation of the F=1, {delta}m{sub F}={+-}1 Zeeman frequency in atomic hydrogen. Here we discuss the theoretical interpretation of this recent experiment, the operating principles of the maser, and the double-resonance technique used to measure the Zeeman frequency. We also describe the characterization of systematic effects and details of the data analysis. We conclude by comparing our result to other recent experiments, and discussing potential improvements to the hydrogen maser double-resonance technique.

Progress in the Development of Hydrogen Masers

The basic operational requirements and present technology for high stability hydrogen maser (H-maser) oscillators are described. Design features of a high stability maser oscillator for use in space, maser operation at 0.5 K and present uses of high stability H-masers are discussed.