Constraint on a Varying Proton-Electron Mass Ratio 1.5 Billion Years after the Big Bang

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, μ . A high resolution spectrum of the J1443+2724 quasar, which was observed with the Very Large Telescope, is used to create an accurate model of 89 Lyman and Werner band transitions whose relative frequencies are sensitive to μ , yielding a limit on the relative deviation from the current laboratory value of Δ μ /μ =(-9.5 ±5.4_stat±5.3_syst)×10^-6 .