Search for $K^{-}pp$ bound state via ${\hat{I}}^{3}d\to K^{+}\ddot{I}{€}^{-}X$ reaction at $E_{\hat{I}}^3=1.5-2.4$ GeV

Abstract

A search for $K^{-}pp$ bound state (the lightest kaonic nucleus) has been performed using the ${\hat{I}}^{3}d\to K^{+}\ddot{I}{€}^{-}\mathrm{X}$ reaction at E${}_{\hat{I}}^3$=1.5-2.4 GeV at LEPS/SPring-8. The differential cross section of $K^{+}\ddot{I}{€}^{-}$ 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 $\hat{I}¼$ b (95 confidence level) for a set of assumed binding energy and width values.