Quasar-Lyman a forest cross-correlation from BOSS DR11: Baryon Acoustic Oscillations

We measure the large-scale cross-correlation of quasars with the Ly alpha forest absorption, using over 164,000 quasars from Data Release 11 of the SDSS-III Baryon Oscillation Spectroscopic Survey. We extend the previous study of roughly 60,000 quasars from Data Release 9 to larger separations, allowing a measurement of the Baryonic Acoustic Oscillation (BAO) scale along the line of sight cl(H(z = 2.36) r(s)) = 9.0 +/- 0.3 and across the line of sight DA(z = 2.36) / r(s) = 10.8 +/- 0.4, consistent with CMB and other BAO data. Using the best fit value of the sound horizon from Planck data (r(s) = 147.49 Mpc), we can translate these results to a measurement of the Hubble parameter of H(z = 2.36) = 226 +/- 8km s(-1)Mpc(-1) and of the angular diameter distance of DA(z = 2.36) = 1590 +/- 60 Mpc. The measured cross-correlation function and an update of the code to fit the BAO scale (baofit) are made publicly available.