Search For Semileptonic Decays In The B Meson Into The Lambda Subscript C Baryon

Search for Semileptonic Decays in the B Meson Into the [Lambda]+[subscript C] Baryon

Evidence for B Semileptonic Decays Into the Lambda_c Charm Baryon

We present the first evidence for B semileptonic decays into the charmed baryon [Lambda]{sub c} based on 420 fb−1 of data collected at the [Upsilon](4S) resonance with the BABAR detector at the PEP-II ee− storage rings. Events are tagged by fully reconstructing one of the B mesons in a hadronic decay mode. We measure the relative branching fraction [Beta]({bar B} 2![Lambda]{sub c}+ Xl−{bar {nu}}{sub {ell}})/[Beta]({bar B} 2![Lambda]{sub c}+/{bar {Lambda}}{sub c}−X) = (3.2 ± 0.9{sub stat.} ± 0.9{sub syst.})%. The significance of the signal including the systematic uncertainty is 4.9 standard deviations.

Searches for the Baryon- and Lepton-number Violating Decays $B^0\rightarrow\Lambda_c^ \ell^-$, $B^-\rightarrow\Lambda\ell^-$, and $B^-\rightarrow\bar{\Lambda}\ell^-$

Searches for B mesons decaying to final states containing a baryon and a lepton are performed, where the baryon is either [Lambda]{sub c} or [Lambda] and the lepton is a muon or an electron. These decays violate both baryon and lepton number and would be a signature of physics beyond the standard model. No significant signal is observed in any of the decay modes, and upper limits in the range (3.2 - 520) x 10−8 are set on the branching fractions at the 90% confidence level.