I'm looking to understand where certain "unexplained" vertices in some Feynman diagrams come from, in a physical sense. For example, in the top figure (Aaij et al. 2015), in diagram (b), there is an "unaccounted for" $u\bar{u}$ pair that seems to come from nowhere.

Are these quarks similar to the spectator quarks from the initial $\Lambda_0^b$, or do they arise from the virtual quark/gluon sea somehow? If they come from the quark sea, how can they come to comprise real, observable particles like the kaon and $P_c^+$?

^{Image source: Observation of $J/\psi p$ resonances consistent with pentaquark states in $Λ^0_b→J/\psi K^−p$ decays, LHCb collaboration. Phys. Rev. Lett. 115, 072001 (2015), arXiv:1507.03414.}

^{Image source: Hidden-charm molecular pentaquarks and their charm-strange partners, R. Chen et al. Nucl. Phys. A 954, 406-421 (2016), arXiv:1601.03233.}