Search for $K^-pp$ bound state via $\gamma d \rightarrow K^+ \pi^-X$ reaction at $E_\gamma=1.5-2.4$ GeV

TL;DR

This study searched for the $K^-pp$ bound state using photon-induced reactions on deuterium, measured the differential cross section, and found no significant evidence of the bound state within the examined energy range.

Contribution

First measurement of $K^+ ext{ and } ext{pi}^-$ photoproduction off deuterium in this energy range, setting upper limits on $K^-pp$ production cross sections.

Findings

No significant bump observed in the missing mass spectrum.

Upper limits on the production cross section were established.

Differential cross sections measured for the first time in this energy region.

Abstract

A search for $K^-pp$ bound state (the lightest kaonic nucleus) has been performed using the $\gamma d \rightarrow K^+ \pi^- \rm{X}$ reaction at E$_\gamma$=1.5-2.4 GeV at LEPS/SPring-8. The differential cross section of $K^+ \pi^-$ photo-production off deuterium has been measured for the first time in this energy region, and a bump structure was searched for in the inclusive missing mass spectrum. A statistically significant bump structure was not observed in the region from 2.22 to 2.36 GeV/$c^2$, and the upper limits of the differential cross section for the $K^-pp$ bound state production were determined to be 0.1$-$0.7 $\mu$ b (95$%$ confidence level) for a set of assumed binding energy and width values.