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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.
Rovibronic molecular hydrogen (H$_2$) transitions at redshift $z_{rm abs} simeq 2.659$ towards the background quasar B0642$-$5038 are examined for a possible cosmological variation in the proton-to-electron mass ratio, $mu$. We utilise an archival sp
Molecular hydrogen (H2) absorption features observed in the line-of-sight to Q2348-011 at redshift zabs = 2.426 are analysed for the purpose of detecting a possible variation of the proton-to-electron mass ratio mu=mp/me. By its structure Q2348-011 i
Molecular transitions recently discovered at redshift z_abs=2.059 toward the bright background quasar J2123-0050 are analysed to limit cosmological variation in the proton-to-electron mass ratio, mu=m_p/m_e. Observed with the Keck telescope, the opti
A molecular hydrogen absorber at a lookback time of 12.4 billion years, corresponding to 10$%$ of the age of the universe today, is analyzed to put a constraint on a varying proton--electron mass ratio, $mu$. A high resolution spectrum of the J1443$+
A limit on a possible cosmological variation of the proton-to-electron mass ratio $mu$ is derived from methanol (CH$_3$OH) absorption lines in the benchmark PKS1830$-$211 lensing galaxy at redshift $z = 0.89$ observed with the Effelsberg 100-m radio