Deuterium/hydrogen in a new Lyman limit absorption system atz= 3.256 towards PKS1937−1009

We have identified a new Lyman limit absorption system towards PKS1937-1009, with log N (H I) = 18.25 0.02 at z = 3.256 that is suitable for measuring deuterium/hydrogen (D/H). We find a 68.3 per cent confidence range for D/H of 1.6 +0.25 -0.30 10 -5 and a 95.4 per cent range of 1.6 +0.5 -0.4 10 -5 . The metallicity of the cloud where D/H was measured is low, Si/H = -2.0 0.5. At these metallicities we expect that D/H will be close to the primordial value. Our D/H is lower than the D/H value predicted using the b calculated from the cosmic background radiation measured by the Wilkinson Microwave Anisotropy Probe, 2.60 +0.19 -0.17 10 -5 . Our result also exacerbates the scatter in D/H values around the mean primordial D/H.