Inclusive spectrum of the d( +, K+) reaction at 1.69 GeV/c

Abstract

We have measured an inclusive missing-mass spectrum of the d( + , K + ) reaction at a pion incident momentum of 1.69 GeV/c at laboratory scattering angles between 2 and 16 with a missing-mass resolution of 2.7 0.1 MeV/c 2 (FWHM) at the missing mass of 2.27 GeV/c 2 . In this letter, we first try to understand the spectrum as a simple quasi-free picture based on several known elementary cross sections, considering the neutron/proton Fermi motion in the deuteron. While gross spectrum structures are well understood in this picture, we have observed two distinct deviations; one peculiar enhancement at 2.13 GeV/c 2 is due to the N cusp, and the other notable feature is a shift of a broad bump structure, mainly originating from hyperon resonance productions of (1405) and (1385) +/0 , by about 22.4 0.4 (stat.) +2.7 -1.7 (syst.) MeV/c 2 toward the low-mass side, which is calculated in the kinematics of a proton at rest as the target.