  Shock/sound propagation from the quenched jets have well-defined front,
separating the fireball into regions which are and are not affected. While even
for the most robust jet quenching observed this increases local temperature and
flow of ambient matter by only few percent at most, strong radial flow
increases the contrast between the two regions so that the difference should be
well seen in particle spectra at some $p_t$, perhaps even on event-by-event
basis. We further show that the effect comes mostly from certain ellipse-shaped
1-d curve, the intercept of three 3-d surfaces, the Mach cone history, the
timelike and spacelike freezeout surfaces. We further suggest that this "edge"
is already seen in an event released by ATLAS collaboration.
