Search for semileptonic decays of the B meson into the lambda charmed baryon

Semileptonic decays of the B meson into baryons are not as well understood, theoretically or experimentally, as the decays into mesons. While there is no reason to believe that these decays are forbidden in the Standard Model, as of yet no theoretical model exists to calculate their decay rate. Difficulty arises because of the limited phase space, which makes the non-perturbative effects in the strong interaction calculation non-negligible. Despite this, some clues about the mechanism of semileptonic B decays can be obtained by comparing the rates of decays into baryons and mesons. Previous experimental work was performed by the CLEO Collaboration where an upper limit was obtained for the semileptonic B decays into baryons.;The analysis presented herein improves on this limit by performing a search of theses decays using the data collected by the BABAR experiment. The search for semileptonic B decays into the L+c charmed baryon is performed using the data collected on the Upsilon(4 S) resonance with the BABAR detector at the PEP-II e+e- asymmetric storage rings located at the Stanford Linear Accelerator Center. The total integrated luminosity of the data is 420.1 fb-1, corresponding to roughly 460 million BB¯ pairs. Events are tagged by fully reconstructing one of the B mesons in a hadronic decay mode. The 90% confidence level upper limit is obtained to be B (B¯ → L+c Xℓ- nℓ&parr0;/B (B¯ → L+c/L-c X) < 2.7%, which takes into account the systematic uncertainties. This upper limit is an improvement over the previous CLEO result.