Of Ap Mass Spectrum from the Reaction : K - D - - - Pa at Rest

An experiment to study hyperon nucleon production in K-D interaction at rest \ was carried out by exposing the BNL 30-inch D2 bubble chamber to a low energy separated K-beam at the AGS. We present here results from the study of reaction K D-n-p A. In particular, a detailed analysis on the Ap mass spectrum near the 2129 MeV region was carried out to determine the nature of the observed enhancement. l-3 Figure 1 exhibits the distribution of events in the two-dimensional mass plot, M(Ap) vs M(A n-). Obvious evidence of structures in the Ap mass system appears both in the low mass region and at around 2130 MeV, while no significant amount of Y*(1385) appears to be in evidence. Strong formation of I = l/2 n-p system is not expected in the allowed mass region. Gaussian ideogram of events projected on the Ap mass axis is shown in Fig. 2a. The distribution contains 2470 events from sample (a) where all particles were measured, and 2431 events from sample (b) where A was missing. The average mass resolution from the two samples are 1.0 MeV and 2.6 MeV, respectively. The events clustering in the low mass region can be attributed to a combination of A production from single nucleon interaction K-n(p)-A(p) with and without subsequent final state A-(p) interaction. A detailed analysis of Fig. 1 indicates that Y*(1385) production is much less than the amount estimated in Ref. 1. The memum estimated reflection from these events can be represented by a very slowly varying function of the mass with an average height of about 10 events per bin and extending from about 2060 to 2145 MeV. The remaining distribution features a striking enhancement with an apparent narrow width at about 2129 MeV and a shoulder that protrudes out to about 2140 MeV. A detailed analysis with the aid of a final state interaction model such as K-D-+-~(N) L AP-2-was carried out. We followed the prescription and the approximation worked. out in Refs. 4 and 5. The result is compared with Fig. 2b which includes only the I higher resolution sample. We have included in the matrix element contribution from the intermediate 2' and co diagrams as well as the interference term. By assuming charge symmetry in ctn and Cop scatterings and by using the EN scattering information, 6 we estimated that the contribution from Co diagram is only about one-seventh …