Constraint on a varying proton-to-electron mass ratio from molecular
  hydrogen absorption toward quasar SDSS J123714.60+064759.5
  Molecular hydrogen transitions in the sub-damped Lyman alpha absorber at
redshift z = 2.69, toward the background quasar SDSS J123714.60+064759.5, were
analyzed in order to search for a possible variation of the proton-to-electron
mass ratio mu 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 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 analyzed in detail from
measurements of asteroid and `solar twin' spectra, and were corrected for. The
final constraint on the relative variation in mu between the absorber and the
current laboratory value is dmu/mu = (-5.4 \pm 6.3 stat \pm 4.0 syst) x
10^(-6), consistent with no variation over a look-back time of 11.4 Gyrs.
