A relativistic description of the A(pi+,K+)_(Λ)A reaction

We investigate the A$(\pi^+,K^+){_\Lambda}$A reaction within a covariant model. We consider those amplitudes which are described by creation, propagation and decay into relevant channel of $N^*$(1650), $N^*$(1710), and $N^*$(1720) intermediate baryonic resonance states in the initial collision of the incoming pion with one of the target nucleons. The bound state nucleon and hyperon wave functions are obtained by solving the Dirac equation with appropriate scalar and vector potentials. Expressions for the reaction amplitudes are derived taking continuum particle wave function in the plane wave approximation. Numerical calculations are presented for reactions on $^{12}$C, $^{40}$Ca, $^{51}$V and $^{89}$Y target nuclei. The predictions of our model are in reasonable agreement with the available experimental data.