Measurements of the Decays B0 ---> anti-D0 p anti-p, B0 ---> anti-D*0 p anti-p, B0 ---> D- p anti-p pi+, and B0 ---> D*- p anti-p pi+

We present measurements of branching fractions of $B^0$ decays to multi-body final states containing protons, based on 232 million $\Upsilon(4S)\to B\bar{B}$ decays collected with the BaBar detector at the SLAC PEP-II asymmetric-energy $B$ factory. We measure the branching fractions ${\cal B}(B^0 \to \bar{D}^0\proton\antiproton)=(1.13\pm0.06\pm0.08)\times 10^{-4}$, ${\cal B}(B^0 \to \bar{D}^{*0}\proton\antiproton)=(1.01\pm0.10\pm0.09)\times 10^{-4}$, ${\cal B}(B^0 \to D^{-}\proton\antiproton\pi^+)=(3.38\pm0.14\pm0.29)\times 10^{-4}$, and ${\cal B}(B^0 \to D^{*-}\proton\antiproton\pi^+)=(4.81\pm0.22\pm0.44)\times 10^{-4}$ where the first error is statistical and the second systematic. We present a search for the charmed pentaquark state, $\Theta_c(3100)$ observed by H1 and put limits on the branching fraction ${\cal B} (B^0 \to \Theta_c \antiproton\pi^+)\times{\cal B}(\Theta_c \to D^{*-}\proton)<14\times10^{-6}$ and ${\cal B}(B^0 \to \Theta_c \antiproton\pi^+)\times{\cal B}(\Theta_c\to D^-\proton)<9\times10^{-6}$. Upon investigation of the decay structure of the above four $B^{0}$ decay modes, we see an enhancement at low $p\bar{p}$ mass and deviations from phase-space in the $\bar{D}\bar{p}$ and $\bar{D}p$ invariant mass spectra.