I'm looking to understand where certain "unexplained" vertices in some Feynman diagrams come from, in a physical sense. For example, in the following 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 $P_c^+$?