  The dead cone is a well-known effect in gauge theories, where radiation from
a charged particle of mass m and energy E is suppressed within an angular size
of m/E. This effect is universal as it does not depend on the spin of the
particle nor on the nature of the gauge interaction. It is challenging to
directly measure the dead cone at colliders, however, since the region of
suppressed radiation either is too small to be resolved or is filled by the
decay products of the massive particle. In this paper, we propose to use jet
substructure techniques to expose the dead cone effect in the strong-force
radiation pattern around boosted top quarks at the Large Hadron Collider. Our
study shows that with 300/fb of 13-14 TeV collision data, ATLAS and CMS could
obtain the first direct evidence of the dead cone effect and test its basic
features.
