Pentaquarks from intrinsic charms in ${\mathrm{\Lambda }}_b$ decays

We study the three-body ${\mathrm{\Lambda }}_b$ decays of ${\mathrm{\Lambda }}_b\to J\mathrm{/}\psi pM$ with $M=K^{-}$ and ${\pi }^{-}$. The two new states ${\cal P}{c1}\equiv {\cal P}c(4380)^+$and${\cal P}{c2}\equiv {\cal P}c(4450)^+$ observed recently as the resonances in the $J\mathrm{/}\psi p$ invariant mass spectrum of $\Lambda_b\to J/\psi p K^-$canbeidentifiedtoconsistoffivequarks,$uudc\bar c$, being consistent with the existence of the pentaquark states. We argue that, in the doubly charmful ${\mathrm{\Lambda }}_b$ decays of ${\mathrm{\Lambda }}_b\to J\mathrm{/}\psi p{K}^{-}$ through $b\to c\bar c s$,apartfromthosethroughthenon-resonant$\Lambda_b\to pK^-$ and resonant ${\mathrm{\Lambda }}_b\to {\mathrm{\Lambda }}^{\ast }\to p{K}^{-}$ transitions, the third contribution with the non-factorizable effects is not the dominant part for the resonant ${\mathrm{\Lambda }}_b\to K^{-}{\mathcal{P}}_{c1,c2},{\mathcal{P}}_{c1,c2}\to J\mathrm{/}\psi p$ processes, such that we propose that the ${\mathcal{P}}_{c1,c2}$ productions are mainly from the charmless ${\mathrm{\Lambda }}_b$ decays through $b\to \bar{u}us$, in which the $c\bar c$contentin${\cal P}{c1,c2}$arisesfromtheintrinsiccharmswithinthe$\Lambda_b$ baryon. We hence predict the observables related to the branching ratios and the direct CP violating asymmetries to be ${\cal B}(\Lambda_b\to \pi^-({\cal P}{c1,c2}\to) J/\psi p)/{\cal B}(\Lambda_b\to K^-({\cal P}{c1,c2}\to) J/\psi p)=0.8\pm 0.1$,${\cal A}{CP}(\Lambda_b\to \pi^-({\cal P}{c1,c2}\to)J/\psi p)=(-3.9\pm 0.2)%$,and${\cal A}{CP}(\Lambda_b\to K^-({\cal P}_{c1,c2}\to)J/\psi p)=(5.8\pm 0.2)%$, which can alleviate the inconsistency between the theoretical expectations from the three contributions in the doubly charmful ${\mathrm{\Lambda }}_b$ decays and the observed data.