Missing-Mass Measurement of the 12C(K-, K+) Reaction at 1.8 GeV/c with the Superconducting Kaon Spectrometer

We performed a measurement of the inclusive missing-mass spectrum of the C-12(K-,K+) reaction at an incident beam momentum of 1.8 GeV/c. This measurement was carried out by using the Superconducting Kaon Spectrometer (SKS) and the K1.8 beamline spectrometer at the Hadron Experimental Facility in J-PARC. From the missing-mass of the 12C(K-,K+) reaction, the binding energy of a Xi- hyperon in a core 11B nucleus, B Xi(-), can be calculated. Our experimental setup yielded a good energy resolution of 8.2 MeV (full width at half maximum), which allowed us to observe significant enhancements in the proximity of the Xi Be-12 production threshold region. In order to extract information from the missing-mass spectrum, we employed several fitting parameters assumptions. A good agreement with the spectrum shape was obtained by adding two Gaussian functions, with the constant experimental resolution for the Xi-hypernuclear states, to the background distribution. The peak positions were obtained to be B Xi-=8.9 +/- 1.4 (stat.) (+3.8)(-3.1) (syst.) MeV and B Xi-=-2.4 +/- 1.3 (stat.) (+2.8)(-1.2) (syst.) MeV. Another model assumption, one Breit-Wigner function with B Xi-=-2.7 +/- 2.2 (stat.) (+0.5)(-0.7) (syst.) MeV and Gamma=4.1 +/- 2.1 (stat.) (+1.2)(-0.7) (syst.) MeV, also yielded a similar chi(2) value.