  We unravel the influence of quasiparticle screening in the non-equilibrium
exciton dynamics of monolayer WS$_2$. We report pump photon energy-dependent
exciton blue and red-shifts from time-resolved-reflectance contrast
measurements. Based on a phenomenological model, we isolate the effective
impact of excitons and free carriers on the renormalization of the quasi-free
particle band gap, exciton binding energy and linewidth broadening. By this,
our work does not only provide a comprehensive picture of the competing
phenomena governing the exciton dynamics in WS$_2$ upon photoexcitation, but
also demonstrates that exciton and carrier contributions to dynamic screening
of the Coulomb interaction differ significantly.

Mesoscale and Nanoscale Physics;Materials Science