  The streaming instability (SI) is a mechanism to aerodynamically concentrate
solids in protoplanetary disks and facilitate the formation of planetesimals.
Recent numerical modeling efforts have demonstrated the increasing complexity
of the initial mass distribution of planetesimals. To better constrain this
distribution, we conduct SI simulations including the self-gravity with
hitherto the highest resolution. To subsequently identify all of the self-bound
clumps, we develop a new clump-finding tool, PLanetesimal ANalyzer
(\texttt{PLAN}). We then apply a maximum likelihood estimator to fit a suite of
parameterized models with different levels of complexity to the simulated mass
distribution. To determine which models are best-fitting and statistically
robust, we apply three model selection criteria with different complexity
penalties. We find that the initial mass distribution of clumps is not
universal regarding both the functional forms and parameter values. Our model
selection criteria prefer models different from those previously considered in
the literature. Fits to multi-segment power law models break to a steeper
distribution above masses close to 100 km collapsed planetesimals, similar to
observed Kuiper Belt size distributions. We find evidence for a turnover in the
low mass end of the planetesimal mass distribution in our high resolution run.
Such a turnover is expected for gravitational collapse, but had not previously
been reported.
