  We report the first angle-resolved photoemission measurement of the
wave-vector dependent plasmon satellite structure of a three-dimensional solid,
crystalline silicon. In sharp contrast to nanomaterials, which typically
exhibit strongly wave-vector dependent, low-energy plasmons, the large plasmon
energy of silicon facilitates the search for a plasmaron state consisting of
resonantly bound holes and plasmons and its distinction from a weakly
interacting plasmon-hole pair. Employing a first-principles theory, which is
based on a cumulant expansion of the one-electron Green's function and contains
significant electron correlation effects, we obtain good agreement with the
measured photoemission spectrum for the wave-vector dependent dispersion of the
satellite feature, but without observing the existence of plasmarons in the
calculations.
