  We used polarization-dependent angle-resolved photoemission spectroscopy
(ARPES) to study the high-energy anomaly (HEA) in the dispersion of
Nd2-xCexCuO4, (x=0.123). We have found that at particular photon energies the
anomalous, waterfalllike dispersion gives way to a broad, continuous band. This
suggests that the HEA is a matrix element effect: it arises due to a
suppression of the intensity of the broadened quasi-particle band in a narrow
momentum range. We confirm this interpretation experimentally, by showing that
the HEA appears when the matrix element is suppressed deliberately by changing
the light polarization. Calculations of the matrix element using atomic wave
functions and simulation of the ARPES intensity with one-step model
calculations provide further proof for this scenario. The possibility to detect
the full quasi-particle dispersion further allows us to extract the high-energy
self-energy function near the center and at the edge of the Brillouin zone.
