Pentaquarks in semileptonic $Λ_b$ decays

Abstract

In terms of ${\cal P}_{c1,c2}={\cal P}_c(4380,4450)^+$ as the hidden charm pentaquark states to consist of $c\bar c uud$, we study the semileptonic $Λ_b\to ({\cal P}_{c1,c2}\to)J/ψp \ell^-\bar ν_\ell$ decays. In our discussion, while the main contribution to $Λ_b\to K^-J/ψp$ is from the non-perturbative process via the doubly charmful $b\to c\bar cs$ transition, we propose that the $Λ_b\to {\cal P}_{c1,c2}\to J/ψp$ transitions are partly contribute to the $Λ_b\to K^-({\cal P}_{c1,c2}\to)J/ψp$ decays, in which the required $c\bar c$ pair is formed by the sea quarks, intrinsic charm, or both. We predict that ${\cal B}(Λ_b\to J/ψp \ell^-\bar ν_\ell)=(2.04^{+4.82}_{-1.57},1.75^{+4.14}_{-1.35})\times 10^{-6}$ for $\ell=(e,μ)$, which are about two orders of magnitude smaller than the observed decay of $Λ_b\to pμ\bar ν_μ$. We also explore the angular correlations for the $J/ψp$ and $\ell^-\bar ν_\ell$ pairs. Our results of the decay branching ratios and angular asymmetries in $Λ_b\to J/ψp \ell^-\bar ν_\ell$, accessible to the ongoing experiments at the LHCb, can be used to improve the understanding of the hidden charm pentaquark states.

11 pages, 3 figures, accepted by Annals of Physics