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 $P_c^+$?

[![enter image description here][1]][1]

<sup>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)](https://doi.org/10.1103/PhysRevLett.115.072001), [arXiv:1507.03414](https://arxiv.org/abs/1507.03414).</sup>

[![enter image description here][2]][2]

<sup>Image source: Hidden-charm molecular pentaquarks and their charm-strange partners, R. Chen et al. [*Nucl. Phys. A* **954**, 406-421 (2016)](http://dx.doi.org/10.1016/j.nuclphysa.2016.04.012), [arXiv:1601.03233](https://arxiv.org/abs/1601.03233).</sup>

  [1]: https://i.sstatic.net/pepz8.png
  [2]: https://i.sstatic.net/ObfGn.png