High-resolution search for the $\Theta^{+}$ pentaquark via a pion-induced reaction at J-PARC

TL;DR

This study conducted a high-resolution search for the $ heta^+$ pentaquark via pion-induced reactions at J-PARC, setting upper limits on its production cross section and constraining its decay width, but found no evidence of its existence.

Contribution

It provides the first high-resolution search for $ heta^+$ at J-PARC with stringent upper limits and decay width constraints, improving previous experimental bounds.

Findings

No sharp peak observed in missing mass spectrum.

Upper limits on production cross section less than 0.28 μb/sr.

Decay width constrained to less than 0.36 MeV for $1/2^+$.

Abstract

The pentaquark $\Theta^+$ has been searched for via the $\pi^-p \to K^-X$ reaction with beam momenta of 1.92 and 2.01 GeV/$c$ at J-PARC. A missing mass resolution of 2 MeV (FWHM) was achieved but no sharp peak structure was observed. The upper limits on the production cross section averaged over the scattering angle from 2$^{\circ}$ to 15$^{\circ}$ in the laboratory frame were found to be less than 0.28 $\mu$b/sr at the 90\% confidence level for both the 1.92- and 2.01-GeV/$c$ data. The systematic uncertainty of the upper limits was controlled within 10\%. Constraints on the $\Theta^+$ decay width were also evaluated with a theoretical calculation using effective Lagrangian. The present result implies that the width should be less than 0.36 and 1.9 MeV for the spin-parity of $1/2^+$ and $1/2^-$, respectively.