Abstract
A limit on a possible cosmological variation of the proton-to-electron mass ratio mu is derived from methanol (CH3OH) absorption lines in the benchmark PKS1830-211 lensing galaxy at redshift z = 0: 89 observed with the Effelsberg 100-m radio telescope, the Institute de Radio Astronomie Millimetrique 30-m telescope, and the Atacama Large Millimeter/submillimeter Array. Ten different absorption lines of CH3OH covering a wide range of sensitivity coefficients K-mu are used to derive a purely statistical 1 sigma constraint of Delta mu/mu = (1.5 +/- 1.5) x 10(-7) for a lookback time of 7.5 billion years. Systematic effects of chemical segregation, excitation temperature, frequency dependence, and time variability of the background source are quantified. A multidimensional linear regression analysis leads to a robust constraint of Delta mu/mu = (-1.0 +/- 0.8(stat) +/- 1.0(sys)) x 10(-7.)