We present a measurement of the D/H abundance ratio in a metal-poor damped Ly \alpha ( DLA ) system along the sightline of QSO SDSS1558-0031 .
The DLA system is at redshift z = 2.70262 , has a neutral column density of \log N _ { HI } = 20.67 \pm 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 \pm 0.04 cm ^ { -2 } , best constrained by the deuterium Lyman-11 line .
We measure \logD / H = -4.48 \pm 0.06 , which when combined with previous measurements along QSO sightlines gives a best estimate of \logD / H = -4.55 \pm 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 \pm 0.0013 \pm 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 } .