  The mass distribution of jets produced in hard processes at the LHC plays an
important role in several jet substructure related studies involving both
Standard Model and BSM physics, especially in the context of boosted heavy
particle searches. We compute analytically the jet-mass distribution for both
Z+jet and dijet processes, for QCD jets defined in the anti-k_t algorithm with
an arbitrary radius R, to next-to-leading logarithmic accuracy and match our
resummed calculation to full leading-order results. We note the important role
played by initial state radiation (ISR) and non-global logarithms explicitly
computed here for the first time for hadron collider observables, as well as
the jet radius dependence of these effects. We also compare our results to
standard Monte Carlo event generators and discuss directions for further
studies and phenomenology.
