How to reveal the exotic nature of the P_c(4450)

TL;DR

This paper investigates whether the P_c(4450) structure is a genuine exotic pentaquark or a kinematical effect, proposing specific measurements to distinguish between these possibilities.

Contribution

It introduces a method to differentiate between a true pentaquark resonance and a kinematical effect using targeted decay measurements.

Findings

The P_c(4450) structure may be a kinematical effect related to the $ ext{χ}_{c1} p$ threshold.

Measuring $ ext{Λ}_b^0 o K^- ext{χ}_{c1} p$ can confirm the nature of the structure.

Additional decay measurements can help determine if the structure is a genuine resonance or a kinematical artifact.

Abstract

The LHCb Collaboration announced two pentaquark-like structures in the $J/\psi p$ invariant mass distribution. We show that the current information on the narrow structure at 4.45 GeV is compatible with kinematical effects of the rescattering from $\chi_{c1} p$ to $J/\psi p$: First, it is located exactly at the $\chi_{c1} p$ threshold. Second, the mass of the four-star well-established $\Lambda(1890)$ is such that a leading Landau singularity from a triangle diagram can coincidentally appear at the $\chi_{c1} p$ threshold, and third, there is a narrow structure at the $\chi_{c1}\,p$ threshold but not at the $\chi_{c0} p$ and $\chi_{c2} p$ thresholds. In order to check whether that structure corresponds to a real exotic resonance, one has to measure the process $\Lambda_b^0\to K^-\chi_{c1} p$. If the $P_c(4450)$ structure exists in the $\chi_{c1} p$ invariant mass distribution as well, then the structure cannot be just a kinematical effect but is a real resonance, otherwise, one cannot conclude the $P_c(4450)$ to be another exotic hadron. In addition, it is also worthwhile to measure the decay $\Upsilon(1S)\to J/\psi p \bar p$: a narrow structure at 4.45 GeV but not at the $\chi_{c0} p$ and $\chi_{c2} p$ thresholds would exclude the possibility of a pure kinematical effect.