Measurement of Baryon Acoustic Oscillations in the Lyman-alpha Forest
  Fluctuations in BOSS Data Release 9
  We use the Baryon Oscillation Spectroscopic Survey (BOSS) Data Release 9
(DR9) to detect and measure the position of the Baryonic Acoustic Oscillation
(BAO) feature in the three-dimensional correlation function in the Lyman-alpha
forest flux fluctuations at a redshift z=2.4. The feature is clearly detected
at significance between 3 and 5 sigma (depending on the broadband model and
method of error covariance matrix estimation) and is consistent with
predictions of the standard LCDM model. We assess the biases in our method,
stability of the error covariance matrix and possible systematic effects. We
fit the resulting correlation function with several models that decouple the
broadband and acoustic scale information. For an isotropic dilation factor, we
measure 100x(alpha_iso-1) = -1.6 ^{+2.0+4.3+7.4}_{-2.0-4.1-6.8} (stat.) +/- 1.0
(syst.) (multiple statistical errors denote 1,2 and 3 sigma confidence limits)
with respect to the acoustic scale in the fiducial cosmological model (flat
LCDM with Omega_m=0.27, h=0.7). When fitting separately for the radial and
transversal dilation factors we find marginalised constraints 100x(alpha_par-1)
= -1.3 ^{+3.5+7.6 +12.3}_{-3.3-6.7-10.2} (stat.) +/- 2.0 (syst.) and
100x(alpha_perp-1) = -2.2 ^{+7.4+17}_{-7.1-15} +/- 3.0 (syst.). The dilation
factor measurements are significantly correlated with cross-correlation
coefficient of ~ -0.55. Errors become significantly non-Gaussian for deviations
over 3 standard deviations from best fit value. Because of the data cuts and
analysis method, these measurements give tighter constraints than a previous
BAO analysis of the BOSS DR9 Lyman-alpha forest sample, providing an important
consistency test of the standard cosmological model in a new redshift regime.
