The deuterium-to-hydrogen abundance ratio toward the QSO SDSS J155810.16-003120.0

We present a measurement of the D/H abundance ratio in a metal-poor damped Ly alpha ( DLA) system along the sight line of QSO SDSS 1558 - 0031. The DLA system is at redshift and has a neutral column density of log N-HI = 20.67 +/- 0.05 cm(-2) and a gas-phase metallicity [ O/H] = - 1.49, which indicates that deuterium astration is negligible. Deuterium absorption is observed in multiple Lyman series with a column density of log N-DI = 16.19 +/- 0.04 cm(-2), best constrained by the deuterium Ly11 line. We measure log D/H = -4.48 +/- 0.06 which when combined with previous measurements along QSO sight lines gives a best estimate of log D/H = -4.55 +/- 0.04, where the 1 sigma error estimate comes from a jackknife analysis of the weighted means. Using the framework of standard big bang nucleosynthesis, this value of D/H translates into a baryon density of Omega(b)h(2) = 0.0213 +/- 0.0013 +/- 0.0004, where the error terms represent the 1 sigma errors from D/H and the uncertainties in the nuclear reaction rates, respectively. Combining our new measurement with previous measurements of D/ H, we no longer find compelling evidence for a trend of D/ H with. N-HI