  The jet quenching phenomenon in heavy ion collisions provides a strong
evidence of the modification of parton shower in the quark-gluon plasma (QGP).
Jet substructure observables can probe various aspects of the jet formation
mechanism. They contain useful information about the QGP and allow us to study
the medium properties in great details. Here we present theoretical
calculations of jet shapes and cross sections in proton-proton and lead-lead
collisions at the LHC using soft-collinear effective theory, with Glauber gluon
interactions in the medium. We find that resumming large logarithms in the jet
substructure calculation is necessary for precise theoretical predictions. The
resummation is performed using renormalization group evolution between
characteristic jet scales. We also find that the medium induces power
corrections to jet shapes. In the end we present the comparison between our
calculations with the recent measurements at the LHC with very good agreement.
Our calculations help initiate precise jet modification studies in heavy ion
collisions.
