Measurements of $\mathcal{B}({\bar{B}}^0\to {\Lambda }_c^{+}\bar{p})$ and $\mathcal{B}(B^{-}\to {\Lambda }_c^{+}\bar{p}{\pi }^{-})$ and Studies of ${\Lambda }_c^{+}{\pi }^{-}$ Resonances

Abstract

We present an investigation of the decays ${\bar{B}}^0\to {\Lambda }_c^{+}\bar{p}$ and $B^{-}\to {\Lambda }_c^{+}\bar{p}{\pi }^{-}$ based on $383\times 10^6$ ${\rm Y}(4S)\to B\bar{B}$ decays recorded with the BABAR detector. We measure the branching fractions of these decays; their ratio is $\mathcal{B}(B^{-}\to {\Lambda }_c^{+}\bar{p}{\pi }^{-})/\mathcal{B}({\bar{B}}^0\to {\Lambda }_c^{+}\bar{p})=15.4\pm 1.8\pm 0.3$. The $B^{-}\to {\Lambda }_c^{+}\bar{p}{\pi }^{-}$ process exhibits an enhancement at the ${\Lambda }_c^{+}\bar{p}$ threshold and is a laboratory for searches for excited charm baryon states. We observe the resonant decays ${\bar{B}}^{-}\to {\Sigma }_c(2455{)}^0\bar{p}$ and $B^{-}\to {\Sigma }_c(2800{)}^0\bar{p}$ but see no evidence for $B^- \to Σ_{c}(2520)^{0} \baver{p}$. This is the first observation of the decay $B^{-}\to {\Sigma }_c(2800{)}^0\bar{p}$; however, the mass of the observed excited ${\Sigma }_c^0$ state is $(2846\pm 8\pm 10)MeV/c^2$, which is somewhat inconsistent with previous measurements. Finally, we examine the angular distribution of the $B^{-}\to {\Sigma }_c(2455{)}^0\bar{p}$ decays and measure the spin of the ${\Sigma }_c(2455{)}^0$ baryon to be 1/2, as predicted by the quark model.

20 pages, 11 postscript figures, published in Physical Review D