  Femtosecond time-resolved photoemission of photoexcited electrons in highly
oriented pyrolytic graphite (HOPG) provides strong evidence for anisotropies of
quasiparticle (QP) lifetimes. Indicative of such anisotropies is a pronounced
anomaly in the energy dependence of QP lifetimes between 1.1 eV and 1.5 eV -
the vicinity of a saddle point in the graphite bandstructure. This is supported
by recent ab initio calculations and a comparison with experiments on
defect-enriched HOPG which reveal that disorder, e.g. defects or phonons,
increases electron energy relaxation rates.
