We measure the large-scale cross-correlation of quasars with the Lyα 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 c /( H ( z = 2.36) r s ) = 9.0±0.3 and across the line of sight D A ( 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±8 km s −1 Mpc −1 and of the angular diameter distance of D A ( 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.

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