Angular Baryon Acoustic Oscillation measure at z=2.225 from the SDSS
  quasar survey
  Following a quasi model-independent approach we measure the transversal BAO
mode at high redshift using the two-point angular correlation function (2PACF).
The analyses done here are only possible now with the quasar catalogue from the
twelfth data release (DR12Q) from the Sloan Digital Sky Survey, because it is
spatially dense enough to allow the measurement of the angular BAO signature
with moderate statistical significance and acceptable precision. Our analyses
with quasars in the redshift interval z = [2.20,2.25] produce the angular BAO
scale theta_BAO = 1.77 +- 0.31 deg with a statistical significance of 2.12
sigma (i.e., 97% confidence level), calculated through a likelihood analysis
performed using the theoretical covariance matrix sourced by the analytical
power spectra expected in the LCDM concordance model. Additionally, we show
that the BAO signal is robust -although with less statistical significance-
under diverse bin-size choices and under small displacements of the quasars'
angular coordinates. Finally, we also performed cosmological parameter analyses
comparing the theta_BAO predictions for wCDM and w(a)CDM models with angular
BAO data available in the literature, including the measurement obtained here,
jointly with CMB data. The constraints on the parameters Omega_M, w_0 and w_a
are in excellent agreement with the LCDM concordance model.
