  Stars with a wide range of masses provide a variety of production sites for
intermediate-to-heavy mass elements. Very massive stars with mass $\geq 8
M_{\odot}$ culminate their evolution by supernova explosions which are presumed
to be the most viable candidate astrophysical sites of r-process
nucleosynthesis. If the models for the supernova r-process are correct, then
nucleosynthesis results could also pose a significant constraint on the remnant
of supernova explosions, $i.e.$ neutron star or black hole. In the case of very
massive core collapse, a remnant stellar black hole is thought to be formed.
Intense neutrino flux from the neutronized core and the neutrino sphere might
suddenly cease during the Kelvin-Helmholtz cooling phase because of the black
hole formation. It is interesting to explore observable consequences of such a
neutrino flux truncation. Arguments have recently been given in the literature
that even the neutrino mass may be determined from the time delay of deformed
neutrino energy spectrum after the cease of neutrino ejection (neutrino cutoff
effect). Here, we study the expected theoretical response of the r-process
nucleosynthesis to the neutrino cutoff effect in order to look for another
independent signature of this phenomenon. We found a sensitive response of the
r-process yield if the neutrino cutoff occurs after the critical time when the
expanding materials in the neutrino-driven wind drop out of the Nuclear
Statistical Equilibrium (NSE). The r-process nucleosynthesis yields change
maximally if the cutoff occurs during the r-process. Using this result,
connected with future detection of the time-variation of SN neutrino spectrum,
we are able to identify when the black hole formation occurs in the course of
SN collapse.
