\sum_{j=1}^N \, \omega^j(\theta_{k})$.

The calculation of the error bars of the 2PACF data points is a sensitive issue. The correct calculation of these errors is either through simulated mocks or equivalently, through the theoretical approach (see, e.g., [@Crocce11a; @Crocce11b; @Norberg; @Friedrich]). In fact, here we obtain them following the analytical covariance matrix method as described in ref. [@Crocce11b].

Firstly, we obtain the analytical angular power spectrum $C_{\ell}$ using the [CAMBsources]{} code [@Challinor][^2], adopting the following setup:\
– a maximum $\ell$ of 720, enough to sample the 2PACF with our binning choice;\
– the $\Lambda$CDM fiducial cosmology, according to Planck’s second data release [@PLA-XIII];\
– a top-hat redshift window of width $\delta z = 0.05$, centred at $z=2.225$, representing the narrow spectroscopic redshift bin analysed here;\
– a linear bias of 4.25, compatible with the one measured for quasars;\
– we included redshift space distortions and gravitational lensing effects, and computed both the linear and non-linear $C_{\ell}$.

Then we obtain the analytical covariance matrix expected in the fiducial cosmology $\Lambda$CDM $$\begin{aligned}
\label{eqCov}
\mbox{\sc Cov}_{\mbox{\footnotesize \,The}}(\theta,\theta') = \frac{2}{f_{\mbox{\footnotesize sky}}} \, 
\sum_{\ell \, \ge \, 0} \, \frac{2 \ell + 1}{(4\pi)^2} \, P_{\ell}(\cos \theta) \, P_{\ell}(\cos \theta') \, 
(C_{\ell} + 1/{\bar{n}})^2 \, ,\end{aligned}$$ 