  Recently, angle-resolved photoemission spectroscopy (ARPES) has revealed a
dispersion anomaly at high binding energy near 0.3-0.5eV in various families of
the high-temperature superconductors. For further studies of this anomaly we
present a new two-dimensional fitting-scheme and apply it to high-statistics
ARPES data of the strongly-overdoped Bi2Sr2CuO6 cuprate superconductor. The
procedure allows us to extract theself-energy in an extended energy and
momentum range. It is found that the spectral function of Bi2Sr2CuO6 can be
parameterized using a small set of tight-binding parameters and a
weakly-momentum-dependent self-energy up to 0.7 eV in binding energy and over
the entire first Brillouin zone. Moreover the analysis gives an estimate of the
momentum dependence of the matrix element, a quantity, which is often neglected
in ARPES analyses.
