2014ApJ...781...31C

We report the discovery of deuterium absorption in the very metal-poor ([Fe/H] = -2.88) damped Lyα system at z_abs= 3.06726 toward the QSO SDSS J1358+6522. On the basis of 13 resolved D I absorption lines and the damping wings of the H I Lyα transition, we have obtained a new, precise measure of the primordial abundance of deuterium. Furthermore, to bolster the present statistics of precision D/H measures, we have reanalyzed all of the known deuterium absorption-line systems that satisfy a set of strict criteria. We have adopted a blind analysis strategy (to remove human bias) and developed a software package that is specifically designed for precision D/H abundance measurements. For this reanalyzed sample of systems, we obtain a weighted mean of (D/H)_p= (2.53±0.04)x10^–5, corresponding to a universal baryon density 100 Ω_b, 0_ h ² = 2.202±0.046 for the standard model of big bang nucleosynthesis (BBN). By combining our measure of (D/H)_pwith observations of the cosmic microwave background (CMB), we derive the effective number of light fermion species, N_eff= 3.28±0.28. We therefore rule out the existence of an additional (sterile) neutrino (i.e., N_eff= 4.046) at 99.3% confidence (2.7σ), provided that the values of N_eff and of the baryon-to-photon ratio (η₁₀) did not change between BBN and recombination. We also place a strong bound on the neutrino degeneracy parameter, independent of the ⁴He primordial mass fraction, Y_P: ξ_D= +0.05±0.13 based only on the CMB+(D/H)_pobservations. Combining this value of ξ_Dwith the current best literature measure of Y_P, we find a 2σ upper bound on the neutrino degeneracy parameter,|ξ| ≤ +0.062.