Constraint on a varying proton-to-electron mass ratio from molecular hydrogen absorption towards quasar SDSS J123714.60+064759.5

Molecular hydrogen transitions in the sub-damped Lyman α absorber at redshift zabs ≃ 2.69, towards the background quasar SDSS J123714.60+064759.5, were analysed in order to search for a possible variation of the proton-to-electron mass ratio μ over a cosmological time-scale. The system is composed of three absorbing clouds where 137 H2 and HD absorption features were detected. The observations were taken with the Very Large Telescope/Ultraviolet and Visual Echelle Spectrograph with a signal-to-noise ratio of 32 per 2.5 km s−1 pixel, covering the wavelengths from 356.6 to 409.5 nm. A comprehensive fitting method was used to fit all the absorption features at once. Systematic effects of distortions to the wavelength calibrations were analysed in detail from measurements of asteroid and ‘solar twin’ spectra, and were corrected for. The final constraint on the relative variation in μ between the absorber and the current laboratory value is Δμ/μ = (−5.4 ± 6.3stat ± 4.0syst) × 10−6, consistent with no variation over a look-back time of 11.4 Gyr.