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

Molecular hydrogen (H-2) absorption in the damped Lyman a system at z(abs) = 2.34 towards quasar SDSS J123437.55+075843.3 is analysed in order to derive 'a constraint on a possible temporal variation of the proton-to-electronmass ratio, mu, over cosmological time-scales. Some 106 H2 and deuterated molecular hydrogen (HD) transitions, covering the range 3290-3726 angstrom, are analysed with a comprehensive fitting technique, allowing for the inclusion of overlapping lines associated with hydrogen molecules, the atomic hydrogen lines in the Lyman a forest as well as metal lines. The absorption model, based on the most recent and accurate rest wavelength for H-2 and HD transitions, delivers a value of Delta mu/mu = (19 +/- 9(stat) +/- 5(syst)) 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 H-2 absorption lines. This is consistent with other measurements of Delta mu/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 Gyr.