| B mesons are unique among well-established non-quarkonium mesons in their ability to decay into baryons. Baryonic B decays offer a wide range of interesting areas of study: they can be used to test our theoretical understanding of rare decay processes involving baryons, search for direct CP violation and study low-energy QCD.; This thesis presents measurements of branching fractions and a study of the decay dynamics of the charmless three-body decays of B meson into pp¯h, final states, where h = pi+, K+, K0S , K*0 or K* +. With a sample of 232 million Upsilon(4S) → BB¯ events collected with the BaBar detector, we report the first observation of the B → pp¯K* 0 decay, and provide improved measurements of branching fractions of the other modes.; The distribution of the three final-state particles is of particular interest since it provides dynamical information on the possible presence of exotic intermediate states such as the hypothetical pentaquark states theta* ++ and theta+ in the mpK+ and mpK0S spectra, respectively, or glueball states (such as the tensor glueball fJ(2220)) in the mpp¯ spectrum. No evidence for exotic states is found and upper limits on the branching fractions are set.; An enhancement at low pp¯ mass is observed in all the B → pp¯h modes, and its shape is compared between the decay modes and with the shape of the time-like proton form factor. A Dalitz plot asymmetry in B → pp¯K+ mode suggests dominance of the penguin amplitude in this decay and disfavors the possibility that the low mass pp¯ enhancement originates from the presence of a resonance below threshold (such as the recently seen baryonium candidate at 1835 MeV/ c2).; We also identify decays of the type B → Xcc¯h → pp¯h, where h = K+, K0S , K*0 or K* +, and Xcc¯ = eta c or J/psi. In particular, we report on the evidence of the B → etacK* + decay and provide a measurement of the width of eta c. |
