  Electrons in graphene behave like Dirac fermions, permitting phenomena from
high energy physics to be studied in a solid state setting. A key question is
whether or not these Fermions are critically influenced by Coulomb
correlations. We performed inelastic x-ray scattering experiments on crystals
of graphite, and applied reconstruction algorithms to image the dynamical
screening of charge in a freestanding, graphene sheet. We found that the
polarizability of the Dirac fermions is amplified by excitonic effects,
improving screening of interactions between quasiparticles. The strength of
interactions is characterized by a scale-dependent, effective fine structure
constant, \alpha *(k,\omega), whose value approaches \alpha * ~ 1/7 at low
energy and large distances. This value is substantially smaller than the
nominal \alpha = 2.2, suggesting that, on the whole, graphene is more weakly
interacting than previously believed.
