  Crossover behaviors from the pair contact process with diffusion (PCPD) and
the driven PCPD (DPCPD) to the directed percolation (DP) are studied in one
dimension by introducing a single particle annihilation/branching dynamics. The
crossover exponents $\phi$ are estimated numerically as $1/\phi \simeq
0.58\pm0.03$ for the PCPD and $1/\phi \simeq 0.49 \pm 0.02$ for the DPCPD.
Nontriviality of the PCPD crossover exponent strongly supports non-DP nature of
the PCPD critical scaling, which is further evidenced by the anomalous critical
amplitude scaling near the PCPD point. In addition, we find that the DPCPD
crossover is consistent with the mean field prediction of the tricritical DP
class as expected.
