CONSTRAINING CHANGES IN THE PROTON-ELECTRON MASS RATIO WITH INVERSION AND ROTATIONAL LINES

We report deep Green Bank Telescope spectroscopy in the redshifted NH3 (1,1), CS 1-0, and H2CO 0(00)-1(01) lines from the z similar to 0.685 absorber toward B0218+357. The inversion (NH3) and rotational (CS, H2CO) line frequencies have different dependences on the proton-electron mass ratio mu, implying that a comparison between the line redshifts is sensitive to changes in mu. A joint three-component fit to the NH3, CS, and H2CO lines yields [Delta mu/mu] = (-3.5 +/- 1.2) x 10(-7), from z similar to 0.685 to today, where the error includes systematic effects from comparing lines from different species and possible frequency-dependent source morphology. Two additional sources of systematic error remain, due to time variability in the source morphology and velocity offsets between nitrogen-bearing and carbon-bearing species. We find no statistically significant (>= 3 sigma) evidence for changes in mu and obtain the stringent 3 sigma constraint, [Delta mu/mu] < 3.6x10(-7), over 6.2 Gyr; this is the best present limit on temporal changes in mu from any technique, and for any look-back time, by a factor greater than or similar to 5.