Assessing the time constancy of the proton-to-electron mass ratio by precision ro-vibrational spectroscopy of a cold molecular beam

We report the design of an experiment that aims to constrain, over a-few-year timescale, the fractional temporal variation of the proton-to-electron mass ratio, beta = m(p)/m(e), at a level of 10(-15)/yr by means of a spectroscopic frequency measurement on a beam of cold CF3H molecules. This is extracted from a buffer-gas-cooling source and then collimated by means of an electrostatic hexapole lens. Employed in a two-photon Ramsey-fringes interrogation scheme, the probe source is based on a mid-infrared quantum cascade laser, phase-locked to a specially-developed optical frequency comb that is ultimately referenced to the Cs primary standard via an optical fiber link. (C) 2014 Elsevier Inc. All rights reserved.