  We study the transverse momentum, $p_T$, broadening of charm and beauty
quarks in the early stage of high energy nuclear collisions. We aim to compare
the diffusion in the evolving Glasma fields with that of a standard,
Markovian-Brownian motion in a thermalized medium with the same energy density
of the Glasma fields. The Brownian motion is studied via Langevin equations
with diffusion coefficients computed within perturbative Quantum
Chromodynamics. We find that for small values of the saturation scale, $Q_s$,
the average $p_T$ broadening in the two motions is comparable, that suggests
that the diffusion coefficient in the evolving Glasma fields is in agreement
with the perturbative calculations. On the other hand, for large $Q_s$ the
$p_T$ broadening in the Langevin motion is smaller than that in the Glasma
fields. This difference can be related to the fact that heavy quarks in the
latter system experience diffusion in strong, coherent gluon fields that leads
to a faster momentum broadening due to memory, or equivalently to a strong
correlation in the transverse plane.
