Constraint on a varying proton-to-electron mass ratio from H2 and HD
  absorption at z = 2.34
  Molecular hydrogen absorption in the damped Lyman-alpha system at z = 2.34
towards quasar Q1232+082 is analyzed in order to derive a constraint on a
possible temporal variation of the proton-to-electron mass ratio, mu, over
cosmological timescales. Some 106 H2 and HD transitions, covering the range
3290-3726 \AA, are analyzed with a comprehensive fitting technique, allowing
for the inclusion of overlapping lines associated with hydrogen molecules, the
atomic hydrogen lines in the Lyman-alpha forest as well as metal lines. The
absorption model, based on the most recent and accurate rest wavelength for H2
and HD transitions, delivers a value of dmu/mu = (19 +/- 9 +/- 5)x 10^(-6). An
attempt to correct the spectrum for possible long-range wavelength distortions
is made and the uncertainty on the distortion correction is included in the
total systematic uncertainty. The present result is an order of magnitude more
stringent than a previous measurement from the analysis of this absorption
system, based on a line-by-line comparison of only 12 prominent and isolated H2
absorption lines. This is consistent with other measurements of dmu/mu from 11
other absorption systems in showing a null variation of the proton-to-electron
mass ratio over a look-back time of 11 Gyrs.
