  We analyze the LIGO/Virgo GWTC-2 catalog to study the primary mass
distribution of the merging black holes. We perform hierarchical Bayesian
analysis, and examine whether the mass distribution has a sharp cutoff for
primary black hole masses below $65 M_\odot$, as predicted in pulsational pair
instability supernova model. We construct two empirical mass functions. One is
a piece-wise function with two power-law segments jointed by a sudden drop. The
other consists of a main truncated power-law component, a Gaussian component,
and a third very massive component. Both models can reasonably fit the data and
a sharp drop of the mass distribution is found at $\sim 50M_\odot$, suggesting
that the majority of the observed black holes can be explained by the stellar
evolution scenarios in which the pulsational pair-instability process takes
place. On the other hand, the very massive sub-population, which accounts for
at most several percents of the total, may be formed through hierarchical
mergers or other processes.
