  We discuss the properties of a system composed by a static plasma traversed
by a jet of particles. Assuming that both the jet and the plasma can be
described using a hydrodynamical approach, and in the conformal limit, we find
that unstable modes arise when the velocity of the jet is larger than the speed
of the sound of the plasma and only modes with momenta smaller than a certain
values are unstable. Moreover, for ultrarelativistic velocities of the jet the
most unstable modes correspond to relative angles between the velocity of the
jet and momentum of the collective mode ~ pi/4. Our results suggest an
alternative mechanism for the description of the jet quenching phenomenon,
where the jet crossing the plasma loses energy exciting colored unstable modes.
In LHC this effect should be seen with an enhanced production of hadrons for
some specific values of their momenta and in certain directions of momenta
space.
