  The substructure of jets produced in an exclusive and a charm-induced dijet
sample in photoproduction and in charged and neutral current interactions has
been studied with the ZEUS detector at HERA. Jets were identified using the
longitudinally invariant k_T cluster algorithm in the laboratory frame. The
substructure of jets has been studied in terms of the jet shape and subjet
multiplicity. Comparisons between the dijet sample and the quark-induced
samples allow an extraction of the jet substructure for gluons.
Leading-logarithm parton-shower Monte Carlo calculations give a good
description of the differences between quark- and gluon-initiated jets. In
neutral current interactions, the measurements have been compared to
next-to-leading-order QCD calculations which are used to make a determination
of the strong coupling constant, alpha_s.
