EXA2011

Formation of $K^{-}pp$ in high-energy $p+p$ collision is an elementary doorway step to excite kaonic nuclear clusters in nuclei. The $K^{-}pp$ system has a structure of ${\mathrm{\Lambda }}^{\ast }$-$p$, where ${\mathrm{\Lambda }}^{\ast }$ is $\mathrm{\Lambda }(1405)$ embedded in the system. We have investigated theoretically how coupled-channel properties of $\mathrm{\Lambda }(1405)$ change inside the quasi-bound system, $K^{-}pp$, by using "generalized optical potentials" which have an advantage to understand physical meanings of the reaction process. The mass spectrum of ${\mathrm{\Lambda }}^{\ast }$ changes its shape drastically from that of $\mathrm{\Lambda }(1405)$ in free space when the binding of ${\mathrm{\Lambda }}^{\ast }$-$p$ increases on the order of 50 MeV. Taking the change of the ${\mathrm{\Lambda }}^{\ast }$ property above-mentioned into account, we have calculated the reaction cross section of $p+p\to K^{+}+X$ for $X=K^{-}pp={\mathrm{\Lambda }}^{\ast }$-$p$ at incident $T_p=2.5-3.0$ GeV in the energy region of DISTO. It is seen that the strength and the shape of $X$ excitation spectra are largely affected by the property change of ${\mathrm{\Lambda }}^{\ast }$, depending on $T_p$ in this energy region of near $\mathrm{\Lambda }(1405)$-production threshold. This strength behavior is an interesting theoretical problem to be clarified toward a new production means of kaonic nuclear clusters not only in the $p+p$ reaction but also in $p$-nucleus and heavy-ion reactions.