Understanding the newly observed heavy pentaquark candidates

TL;DR

This paper investigates how anomalous triangle singularity (ATS) transitions contribute to the observed heavy pentaquark candidates, revealing that some peaks may be due to kinematic effects rather than genuine exotic states.

Contribution

It demonstrates that ATS transitions can produce peaks similar to pentaquark signals, offering an alternative explanation for observed enhancements in heavy baryon decays.

Findings

Multiple thresholds contribute to pentaquark candidate enhancements.

An additional peak around 4.5 GeV can be generated by ATS.

Threshold interactions with ATS are a general phenomenon affecting exotic state interpretations.

Abstract

We find that several thresholds can contribute to the enhancements of the newly observed heavy pentaquark candidates $P_c^+(4380)$ and $P_c^+(4450)$ via the anomalous triangle singularity (ATS) transitions in the specific kinematics of $\Lambda_b\to J/\psi K^- p$. Apart from the observed two peaks we find that another peaks around 4.5 GeV can also be produced by the ATS. We also show that the $\Sigma_c^{(*)}$ can be produced at leading order in $\Lambda_b$ decay. This process is different from the triangle diagram and its threshold enhancement only appears as CUSP effects if there is no pole structure or the ATS involved. The threshold interaction associated with the presence of the ATS turns out to be a general phenomenon and plays a crucial role in the understanding of candidates for exotic states.