Double triangle cusps relevant to Pc(4312)+ , Pc(4380)+, and Pc(4457)+
Keywords:Pentaquark, kinematical singularities
A novel scenario is proposed for hidden charm pentaquark (Pc)-like structures in Λ 0 b → J/ψpK−. The scenario is based on kinematical singularities arising from double triangle mechanisms. Anomalous threshold cusps due to the singularities are, compared with ordinary P(∗) c D¯(∗) one-loop thresh-old cusp, significantly more singular. It is demonstrated that an interference among the double triangle mechanisms and other common mechanisms generates peaks very similar to the Pc(4312)+, Pc(4380)+, and Pc(4457)+ peak structures. While hadron molecules and compact pentaquarks have been common models to explain the Pc states, the present model is a completely different one. The present model includes only one pentaquark state Pc(4440)+. However, we find that the Pc(4440)+ width and strength are significantly smaller than those from the LHCb analysis. The P + c signals are searched for in J/ψ photoproduction but not found. A search was also made in Λ 0 b → J/ψpπ− data, finding only a possible P c(4440)+-like signal. The present model is consistent with the experimental situation
i. The hadron naming scheme of Ref.  will be used. However, we often use abbreviations such as Σc, Σ ∗ c , Λ ∗ c , and Λ ∗∗ c for Σc(2455)+(++) , Σc(2520)+(++) , Λc(2595)+, and Λc(2625)+, respectively; Yc refers to Λ (∗,∗∗) c and Σ (∗) c collectively. The notation BM(J P ) stands for a baryon (B) and a meson (M) paired in a spin-parity J P .
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