Keck telescope constraint on cosmological variation of the proton-to-electron mass ratio

Understand

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 optical echelle spectrum has the highest resolving power and largest number (86) of H_2 transitions in such analyses so far.
• Also, (seven) HD transitions are used for the first time to constrain mu-variation.
• These factors, and an analysis employing the fewest possible free parameters, strongly constrain mu's relative deviation from the current laboratory value: dmu/mu =(+5.6+/-5.5_stat+/-2.9_sys)x10^{-6}, indicating an insignificantly larger mu in the absorber.