COA−Xsystem for constraining cosmological drift of the proton-electron mass ratio

Abstract

The A 1 − X 1 + band system of carbon monoxide, which has been detected in six highly redshifted galaxies (z = 1.6-2.7), is identified as a probe method to search for possible variations of the proton-electron mass ratio (μ) on cosmological time scales. Laboratory wavelengths of the spectral lines of the A − X (v,0) bands for v = 0-9 have been determined at an accuracy of λ/λ = 1.5 × 10 −7 through VUV Fourier-transform absorption spectroscopy, providing a comprehensive and accurate zero-redshift data set. For the (0,0) and (1,0) bands, two-photon Doppler-free laser spectroscopy has been applied at the 3 × 10 −8 accuracy level, verifying the absorption data. Sensitivity coefficients K μ for a varying μ have been calculated for the CO A − X bands so that an operational method results to search for μ variation.

Perturbations in the A1Π,v= 0 state of12C18O investigated via complementary spectroscopic techniques

“…16 O main isotopologue [24][25][26][27], and in the 13 state and determine whether it shows anomalous behaviour in common with observations of the a 3 state [31,32]. The new spectroscopic measurements of A 1 (v = 0) state presented here are necessary to obtain the precision required to probe this effect.…”

Perspective: Tipping the scales: Search for drifting constants from molecular spectra

“…This definition of K μ yields opposite signs to that used in Refs. [25][26][27]. Although electronic transitions in atoms are sensitive to α, they are relatively immune to a variation of μ.…”

“…In order to prepare for a μ-variation analysis, accurate laboratory measurements on the A − X system of CO were performed, using laser-based excitation and Fouriertransform absorption spectroscopy, 27 yielding transition frequencies at an accuracy better than λ/λ = 3 × 10 −7 . Also a calculation of K μ sensitivity coefficients was performed, which required a detailed analysis of the structure of the A 1 state of CO and its perturbation by a number of nearby lying singlet and triplet states.…”

The status of varying constants: a review of the physics, searches and implications

“…At higher redshifts, optical/near UV measurements are done using molecular hydrogen as first suggested in [40]. Carbon monoxide is less common but has sensitivity coefficients similar to those of molecular hydrogen [89], and can certainly provide important independent tests. The ultimate goal here is to find other molecules at higher redshifts, enabling optical and radio measurements in the same targets.…”