Petitjean, PatrickIvanchik, A.Srianand, R.et al.2012-03-092012-03-092011-07-06http://hdl.handle.net/11007/987We have measured with high precision the position of 79 molecular hydrogen absorption lines of Lyman and Werner bands from two absorption systems at zabs = 2.594733 and 3.024899, in the spectra of quasars Q 0405–443 and Q 0347–383, respectively, in order to constrain the cosmological variation of the proton-to-electron mass ratio, µ = mp/me.Dataareof the highest spectral resolution (R = 53 000) and signal to noise ratio (S/N = 30–70) for such quasars. The absorption lines are not saturated and their profiles can be modelled as simple Gaussian functions. We find a correlation between the observed redshift of the lines and the sensitivity of the line positions to a change in µ. This can be interpreted as a variation of µ with µ/µ = (2.97 ± 0.74) × 10−5 over the past ∼12 Gyrs. As this result is based on two systems one cannot rule out that unknown systematics could cause a false-alarm detection. Thus the result needs to be confirmed with additional data. It is also very important to improve the accuracy of the laboratory wavelengths as the significance of our result depends on the accuracy to which they are known.enProton-to-electron mass ratioMass ratioArticle