New limit on a varying proton-to-electron mass ratio from high-resolution optical quasar spectra

TL;DR

This study uses high-resolution optical spectra of a distant quasar to place new limits on the possible variation of the proton-to-electron mass ratio over cosmological timescales, employing molecular hydrogen and HD transitions.

Contribution

It introduces the first analysis using HD transitions to constrain mu-variation and provides the most precise Keck-based limit to date on mu's variation at this redshift.

Findings

Measured deviation of mu: (+5.6±5.5_stat±2.7_sys)×10^{-6}

Used the highest resolution spectrum with 86 H_2 transitions

First to incorporate HD transitions in such constraints

Abstract

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 spectrum has the highest resolving power and largest number (86) of H_2 transitions in such analyses so far. Also, (7) 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+/-2.7_sys)x10^{-6}. This is the first Keck result to complement recent constraints from three systems at z_abs>2.5 observed with the Very Large Telescope.