  We propose a new search strategy for high-multiplicity hadronic final states.
When new particles are produced at threshold, the distribution of their decay
products is approximately isotropic. If there are many partons in the final
state, it is likely that several will be clustered into the same large-radius
jet. The resulting jet exhibits substructure, even though the parent states are
not boosted. This "accidental" substructure is a powerful discriminant against
background because it is more pronounced for high-multiplicity signals than for
QCD multijets. We demonstrate how to take advantage of accidental substructure
to reduce backgrounds without relying on the presence of missing energy. As an
example, we present the expected limits for several R-parity violating gluino
decay topologies. This approach allows for the determination of QCD backgrounds
using data-driven methods, which is crucial for the feasibility of any search
that targets signatures with many jets and suppressed missing energy.
