The clustering of galaxies in the SDSS-III Baryon Oscillation
  Spectroscopic Survey: Measuring D_A and H at z=0.57 from the Baryon Acoustic
  Peak in the Data Release 9 Spectroscopic Galaxy Sample
  We present measurements of the angular diameter distance to and Hubble
parameter at z=0.57 from the measurement of the baryon acoustic peak in the
correlation of galaxies from the Sloan Digital Sky Survey III Baryon
Oscillation Spectroscopic Survey. Our analysis is based on a sample from Data
Release 9 of 264,283 galaxies over 3275 square degrees in the redshift range
0.43<z<0.70. We use two different methods to provide robust measurement of the
acoustic peak position across and along the line of sight in order to measure
the cosmological distance scale. We find D_A(0.57) = 1408 +/- 45 Mpc and
H(0.57) = 92.9 +/- 7.8 km/s/Mpc for our fiducial value of the sound horizon.
These results from the anisotropic fitting are fully consistent with the
analysis of the spherically averaged acoustic peak position presented in
Anderson et al, 2012. Our distance measurements are a close match to the
predictions of the standard cosmological model featuring a cosmological
constant and zero spatial curvature.
