Search for the $\Theta^{+}$ pentaquark via the $\pi^-p\to K^-X$ reaction at 1.92 GeV/$c$

TL;DR

A search for the $ heta^+$ pentaquark was conducted at J-PARC using a $\pi^-$ beam, but no evidence was found, setting upper limits on its production cross section and decay width.

Contribution

This study provides the first experimental upper limits on the $ heta^+$ pentaquark production cross section and decay width at 1.92 GeV/$c$ beam momentum.

Findings

No peak structure observed in the missing-mass spectrum.

Upper limit of the production cross section is 0.26 μb/sr.

Decay width upper limits are 0.72 MeV/$c^2$ for $J^P=1/2^+$ and 3.1 MeV/$c^2$ for $J^P=1/2^-$.

Abstract

The $\Theta^+$ pentaquark baryon was searched for via the $\pi^-p\to K^-X$ reaction in a missing-mass resolution of 1.4 MeV/$c^2$(FWHM) at J-PARC. $\pi^-$ meson beams were incident on the liquid hydrogen target with the beam momentum of 1.92 GeV/$c$. No peak structure corresponding to the $\Theta^+$ mass was observed. The upper limit of the production cross section averaged over the scattering angle of 2$^{\circ}$ to 15$^{\circ}$ in the laboratory frame was obtained to be 0.26 $\mu$b/sr in the mass region of 1.51$-$1.55 GeV/$c^2$.The upper limit of the $\Theta^+$ decay width using the effective Lagrangian approach was obtained to be 0.72 MeV/$c^2$ and 3.1 MeV/$c^2$ for $J^P_{\Theta}=1/2^+$ and $J^P_{\Theta}=1/2^-$, respectively.