Classical and semiclassical description of initial distributions of kaon capture by atomic hydrogen and deuterium

The moderation and capture of negative kaons by atomic hydrogen and deuterium were investigated by the classical trajectory Monte–Carlo (CTMC) and the semiclassical fermion molecular dynamics (FMD) methods. The dependence of ionization and capture cross sections on initial kaon energy was also studied. The initial populations of kaonic atom levels were calculated. The n distributions of kaonic atoms peaked close to the orbital giving optimum overlap with the displaced electronic orbital. The angular momentum distributions, l, are found to be approximately statistical but cut off at large l smaller than lmax = n − 1 in large n. The results are compared with the adiabatic ionization, diabatic states, and Born approximation methods. The FMD results were found to be in better agreement with quantum mechanical calculations than the ones from CTMC. The kaon kinetic energy spectrum prior to capture was calculated, which reveals that capture occurs at small collision energies up to the ionization energy. Also, the calculations show that kaonic hydrogen (deuterium) atoms have kinetic energies below 0.3 a.u. (0.15 a.u.) after formation.