Observation and study of the baryonic B-meson decays B → D^(*)pp(π)(π)

We present results for B-meson decay modes involving a charm meson, protons, and pions using 455×106 BB̅ pairs recorded by the BaBar detector at the SLAC PEP-II asymmetric-energy e^+e^- collider. The branching fractions are measured for the following ten decays: B ^0→D^0pp, B^0→D^(*0)pp, B^0→D^(*+)ppπ^-, B^0→D^(*+)ppπ^-, B-→D0ppπ^-, B-→D^(*0)ppπ^-, B^0→D^0pp π^-π^+, B^0→D^(*0)pp π^-π^+, B^-→D^+pp π^-π^-, and B^-→D^(*+)pp π^-π^-. The four B^- and the two five-body B^0 modes are observed for the first time. The four-body modes are enhanced compared to the three- and the five-body modes. In the three-body modes, the M(pp) and M(D^((*)0)p) invariant-mass distributions show enhancements near threshold values. In the four-body mode B^0→D^+ppπ^-, the M(pπ^-) distribution shows a narrow structure of unknown origin near 1.5  GeV/c^2. The distributions for the five-body modes, in contrast to the others, are similar to the expectations from uniform phase-space predictions.