Investigating the low-energy K⁻ interactions in nuclear matter with AMADEUS

The AMADEUS collaboration studies low-energy K⁻ interactions with light nuclei in order to clarify some aspects related to the behaviour of hadrons containing strangeness in nuclear medium. One of the main topics is the quest about the possible formation of Kaonic Nuclear Clusters (KNC), which depends on the strength of the anti-kaons interaction with nucleons. In kaonic absorption experiments, the search for KNC is strictly connected with the measurement of the yields of the so-called multi-nucleon absorption processes. In this paper, the study of Σ⁰p correlated production from K⁻ absorption in ¹²C, using the KLOE 2004-2005 data set, is reported. The yield of the two nucleon absorption (2NA), when the produced Σ⁰ and p particles are free from any final state interaction process, was measured for the first time. The contribution of a ppK⁻ bound state was also tested. The best fit is obtained for a ppK⁻ state with a binding energy of 45 MeV and a width of 30 MeV, but the statistical significance is at the level of 1 σ only. (paper)