Studies on the $K^*\Sigma$ bound-state via $K^+p\to K^+\phi\,p$

TL;DR

This study investigates the potential existence of a $K^* ext{-} ext{Sigma}$ bound state, a pentaquark molecule, through the $K^+p o K^+ ext{ } ext{phi} ext{ }p$ reaction using an effective Lagrangian approach, revealing a small but notable signal.

Contribution

It introduces a novel analysis of the $K^* ext{-} ext{Sigma}$ pentaquark state in the $K^+p$ reaction with detailed modeling and considers background reduction techniques.

Findings

A small peak signal indicating the $K^* ext{-} ext{Sigma}$ bound state.

The $K^*(1680,1^-)$ meson significantly influences the results.

Proton-spin polarization helps reduce background effects.

Abstract

In the present work, we investigate the hidden-strangeness production process in the $S=+1$ channel via $K^+p\to K^+\phi\,p$, focussing on the exotic \textit{pentaquark} molecular $K^*\Sigma$ bound state, assigned by $P^+_s(2071,3/2^-)$. For this purpose, we employ the effective Lagrangian approach in the tree-level Born approximation. Using the experimental and theoretical inputs for the exotic state and for the ground-state hadron interactions, the numerical results show a small but obvious peak structure from $P^+_s$ with the signal-to-background ratio $\approx1.7\,\%$, and it is enhanced in the backward-scattering region of the outgoing $K^+$ in the center-of-mass frame. We also find that the contribution from the $K^*(1680,1^-)$ meson plays an important role to reproduce the data. The proton-spin polarizations are taken into account to find a way to reduce the background. The effects of the possible $27$-plet pentaquark $\Theta^{++}_{27}$ is discussed as well.