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 $\Lambda^*$-$p$, where $\Lambda^*$ is $\Lambda(1405)$ embedded in the system. We have investigated theoretically how coupled-channel properties of $\Lambda(1405)$ 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 $\Lambda^*$ changes its shape drastically from that of $\Lambda(1405)$ in free space when the binding of $\Lambda^*$-$p$ increases on the order of 50 MeV. Taking the change of the $\Lambda^*$ property above-mentioned into account, we have calculated the reaction cross section of $p + p \rightarrow K^+ + X$ for $X=K^-pp=\Lambda^*$-$p$ 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 $\Lambda^*$, depending on $T_p$ in this energy region of near $\Lambda(1405)$-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.