First cosmological constraints on the proton-to-electron mass ratio from
  observations of rotational transitions of methanol
  We have used the Australia Telescope Compact Array to measure the absorption
from the 2(0) - 3(-1}E 12.2 GHz transition of methanol towards the z=0.89
lensing galaxy in the PKS B 1830-211 gravitational lens system. Comparison of
the velocity of the main absorption feature with the published absorption
spectrum from the 1(0) - 2(-1)E transition of methanol shows that they differ
by -0.6 +/- 1.6 km/s . We can use these observations to constrain the changes
in the proton-to-electron mass ratio from z=0.89 to the present to 0.8 +/- 2.1
x 10^-7. This result is consistent, and of similar precision to recent
observations at z = 0.68 achieved through comparison of a variety of rotational
and inversion transitions, and approximately a factor of 2 better than previous
constraints obtained in this source. Future more sensitive observations which
incorporate additional rotational methanol transitions offer the prospect of
improving current results by a factor of 5-10.
