  The full three dimensional dispersion of the pi-bands, Fermi velocities and
effective masses are measured with angle resolved photoemission spectroscopy
and compared to first-principles calculations. The band structure by
density-functional theory strongly underestimates the slope of the bands and
the trigonal warping effect. Including electron-electron calculation on the
level of the GW approximation, however, yields remarkable agreement in the
vicinity of the Fermi level. This demonstrates the breakdown of the independent
electron picture in semi-metallic graphite and points towards a pronounced role
of electron correlation for the interpretation of transport experiments and
double-resonant Raman scattering for a wide range of carbon based materials.
