  Photo-induced charge separation in transition metal dichalcogenide
heterobilayers is being explored for moir\'e excitons, spin-valley
polarization, and quantum phases of excitons/electrons. While different
momentum spaces may be critically involved in charge separation dynamics,
little is known directly from experiments. Here we determine momentum-resolved
electron dynamics in the WS2/MoS2 heterobilayer using time and angle resolved
photoemission spectroscopy (TR-ARPES). Upon photoexcitation in the K valleys,
we detect electrons in M/2, M, and Q valleys/points on time scales as short as
~70 fs, followed by dynamic equilibration in K and Q valleys in ~400 fs. The
interlayer charge transfer is accompanied by momentum-specific band
renormalization. These findings reveal the essential role of phonon scattering,
the coexistence of direct and indirect interlayer excitons, and constraints on
spin-valley polarization.
