New constraint on cosmological variation of the proton-to-electron mass ratio from Q0528−250

Molecular hydrogen transitions in quasar spectra can be used to constrain variation in the proton-to-electron mass ratio, μ≡ mp/me, at high redshifts (z ≳ 2). We present here an analysis of a new spectrum of the quasar Q0528−250, obtained on Very Large Telescope (VLT)/Ultraviolet and Visual Echelle Spectrograph (UVES), and analyse the well-known H2 absorber at z = 2.811 in this spectrum. For the first time we detect deuterated molecular hydrogen (HD) in this system with a column density of log10(N/cm−2) = 13.27 ± 0.07; HD is sensitive to variation in μ, and so we include it in our analysis. Using 76 H2 and seven HD transitions we constrain variation in μ from the current laboratory value to be Δμ/μ= (0.3 ± 3.2stat± 1.9sys) × 10−6, which is consistent with no cosmological variation in μ, as well as with previous results from other H2/HD absorbers. The main sources of systematic uncertainty relate to accurate wavelength calibration of the spectra and the re-dispersion of multiple telescope exposures on to the one pixel grid.