  The mechanism of CP violation remains one of the puzzles in particle physics.
Key to understanding this phenomenon are nonleptonic $B$ decays, especially
multibody decays which exhibit large CP asymmetries in various regions of phase
space. A full QCD-based theoretical description of these decays is still
missing, requiring the use of models to fit the data. In this paper, we suggest
a model ansatz which reflects the underlying physics and the known mechanism of
CP violation via the CKM matrix. In addition, since CP violation is driven by
the interference between amplitudes with and without valence charm quarks, we
argue that the opening of the open-charm threshold may play an important role
in generating CP violation in the high invariant mass region. We present a
natural extension of the isobar model to incorporate these effects. We suggest
an analysis of nonleptonic three-body $B$ decay data including this extension,
which would be interesting as it may give new hints to the sources of CP
violation both at low and high invariant mass.

High Energy Physics - Phenomenology;High Energy Physics - Experiment