  Using high resolution x-ray absorption spectroscopy and state-of-the-art
electronic structure calculations we demonstrate that the pre-edge region at
the Cu K-edge of high T$_c$ cuprates is composed of several
excitationsinvisible in standard X-ray absorption spectra. We consider in
detail the case of Ca$_{2-x}$CuO$_2$Cl$_2$ and show that the many pre-edge
excitations (two for c-axis polarization, four for in-plane polarization and
out-of-plane incident X-ray momentum) are dominated by off-site transitions and
intersite hybridization. This demonstrates the relevance of approaches beyond
the single-site model for the description of the pre-edges of correlated
materials. Finally, we show the occurrence of a doubling of the main edge peak
that is most visible when the polarization is along the c-axis. This doubling,
that has not been seen in any previous absorption data in cuprates, is not
reproduced by first principles calculations. We suggest that this peak is due
to many-body charge-transfer excitations, while all the other visible far-edge
structures are single particle in origin. Our work indicates that previous
interpretations of the Cu K-edge X-ray absorption spectra in high T$_c$
cuprates can be profitably reconsidered.
