High-resolution search for the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mi>Θ</mml:mi><mml:mo>+</mml:mo></mml:msup></mml:math>pentaquark via a pion-induced reaction at J-PARC

Abstract

The pentaquark ${\ensuremath{\Theta}}^{+}$ has been searched for via the ${\ensuremath{\pi}}^{\ensuremath{-}}p\ensuremath{\rightarrow}{K}^{\ensuremath{-}}X$ 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 ${2}^{\ensuremath{\circ}}$ to ${15}^{\ensuremath{\circ}}$ in the laboratory frame were found to be less than 0.28 $\ensuremath{\mu}\mathrm{b}/\mathrm{sr}$ 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 ${\ensuremath{\Theta}}^{+}$ decay width were also evaluated with a theoretical calculation using an 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 $1/{2}^{\ensuremath{-}}$, respectively.