  In these proceedings, we report on our numerical lattice simulations of
partons traversing the boost-invariant, non-perturbative glasma as created at
the early stages of collisions at RHIC and LHC. Since these highly energetic
partons are produced from hard scatterings during heavy-ion collisions, they
are already affected by the first stage of the medium's time evolution, the
glasma, which is the pre-equilibrium precursor state of the quark-gluon plasma.
We find that partons quickly accumulate transverse momentum up to the
saturation momentum during the glasma stage. Moreover, we observe an
interesting anisotropy in transverse momentum broadening of partons with larger
broadening in the rapidity than in the azimuthal direction. Its origin can be
related to correlations among the longitudinal color-electric and
color-magnetic flux tubes in the initial state of the glasma. We compare these
observations to the semi-analytic results obtained by a weak-field
approximation, where we also find such an anisotropy in a parton's transverse
momentum broadening.
