  We observe nonlinear scattering of 39 K atomic bright solitons launched in a
one-dimensional (1D) speckle disorder. We directly compare it with the
scattering of non-interacting particles in the same disorder. The atoms in the
soliton tend to be collectively either reflected or transmitted, in contrast
with the behavior of independent particles, thus demonstrating a clear
nonlinear effect in scattering. The observed strong fluctuations in the
reflected fraction, between zero and 100%, are interpreted as a consequence of
the strong sensitivity of the system to the experimental conditions and in
particular to the soliton velocity. This behavior is reproduced in a mean-field
framework by Gross-Pitaevskii simulations, and mesoscopic quantum
superpositions of the soliton being fully reflected and fully transmitted are
not expected for our parameters. We discuss the conditions for observing such
superpositions, which would find applications in atom interferometry beyond the
standard quantum limit.
