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Molecular hydrogen absorption in the damped Lyman-alpha system at z = 2.34towards quasar Q1232+082 is analyzed in order to derive a constraint on apossible temporal variation of the proton-to-electron mass ratio, mu, overcosmological timescales. Some 106 H2 and HD transitions, covering the range3290-3726 \AA, are analyzed with a comprehensive fitting technique, allowingfor the inclusion of overlapping lines associated with hydrogen molecules, theatomic hydrogen lines in the Lyman-alpha forest as well as metal lines. Theabsorption model, based on the most recent and accurate rest wavelength for H2and HD transitions, delivers a value of dmu/mu = (19 +/- 9 +/- 5)x 10^(-6). Anattempt to correct the spectrum for possible long-range wavelength distortionsis made and the uncertainty on the distortion correction is included in thetotal systematic uncertainty. The present result is an order of magnitude morestringent than a previous measurement from the analysis of this absorptionsystem, based on a line-by-line comparison of only 12 prominent and isolated H2absorption lines. This is consistent with other measurements of dmu/mu from 11other absorption systems in showing a null variation of the proton-to-electronmass ratio over a look-back time of 11 Gyrs.

Constraint on a varying proton-to-electron mass ratio from H2 and HD absorption at z = 2.34