right ascension and declination coordinates of the quasars $A$ and $B$, respectively [@Landy-Szalay; @Sanchez11; @Crocce11a].

To find the angular scale $\theta_{\mbox{\footnotesize\sc fit}}$ of the BAO bump in the 2PACF we use the method proposed in Sánchez et al., 2011 [@Sanchez11], which is based on the empirical parametrization of $\omega = \omega(\theta)$ $$\begin{aligned}
\label{ajuste}              
\omega(\theta) = A + B\theta^{\,\gamma} + C\exp^{-(\theta-\theta_{\rm FIT}) / 2\sigma_{\rm FIT}^{2}} \, ,
\label{eq3}\end{aligned}$$ where $A$, $B$, $C$, $\gamma$, $\theta_{\mbox{\footnotesize\sc fit}}$, and $\sigma_{\mbox{\footnotesize\sc fit}}$ are free parameters. Therefore, the 2PACF best-fitting empirical expression (Eq. \[eq3\]) provides $\theta_{\mbox{\footnotesize\sc fit}}$, while the width of the bump, $\sigma_{\mbox{\footnotesize\sc fit}}$, define the error associated to the measured $\theta_{\mbox{\footnotesize\sc fit}}$. The final determination of the acoustic peak is achieved after accounting for an effect that produces a small displacement of the BAO bump, as we discuss below.

The finite thickness $\delta z$ of the shell containing the data produces a shift in the acoustic peak due to a [*projection effect*]{}. To understand this effect consider first all quasars on a spherical shell with radius equal to the characteristic BAO scale and centred on another quasar, therefore contributing to the BAO bump in a 3D analysis, where the central quasar is located at 