Evidence of Ξ hypernuclear production in the ¹²C(K^-,K⁺)¹²_ΞBe reaction

The E885 Collaboration utilized the 1.8 GeV/cK^- beam line at the Alternating Gradient Synchrotron (AGS) to accumulate greater than 10 times the world's existing data sample of (K^-,K⁺) events on carbon. A total of about 3 × 10⁵ (K^-,K⁺) events were collected and analyzed. Ξ hypernuclear states are expected to be produced through the reaction K^-+ ¹²C-→K⁺+ ¹²_ΞBe. A signal could also result from direct production of ¹¹_ΛBe + Λ without a distinct Ξ intermediate state. The measured missing-mass spectrum indicates the existence of a signal below the threshold for free Ξ^- production that cannot be explained by background or effects of limited resolution. Although the resolution was not sufficient to resolve discrete hypernuclear states, the excess of events in the region of missing mass, kinematically inaccessible in free Ξ^- production, can be compared with theoretical predictions for ¹²_ΞBe production. Reasonable agreement between the data and theory is achieved by assuming a Ξ-nucleus potential well depth V_0Ξ of about 14 MeV within the Woods-Saxon prescription.