| Popis: |
To search for an $S = -1$ di-baryonic state which decays to $\Lambda p$, the $^3$He$(K^-,\Lambda p)n_{\rm missing}$ reaction was studied at 1.0 GeV/$c$. Unobserved neutrons were kinematically identified from the missing mass $M_X$ of the $^3$He$(K^-, \Lambda p)X$ reaction in order to have a large acceptance for the $\Lambda pn$ final state. The observed $\Lambda pn$ events, distributed widely over the kinematically allowed region of the Dalitz plot, establish that the major component comes from a three-nucleon absorption process. A concentration of events at a specific neutron kinetic energy was observed in a region of low momentum transfer to the $\Lambda p$. To account for the observed peak structure, the simplest $S$-wave pole was assumed to exist in the reaction channel, having a Breit-Wigner form in energy and with a Gaussian form factor. A minimum $\chi^2$ method was applied to deduce its mass, $M_X = 2355^{+6}_{-8}({\rm stat.}) \pm 12({\rm syst.})$ MeV/$c^2$, and decay width, $\Gamma_X = 110^{+19}_{-17}({\rm stat.}) \pm 27({\rm syst.})$ MeV/$c^2$, respectively. The form factor parameter $Q_X \sim 400$ MeV/$c$ implies that the range of the interaction is about 0.5 fm. |
