Investigating $\pi ^{-}$ production in central $^{7}\text {Be}+^{9}\text {Be}$ and $^{40}\text {Ar}+ ^{45}\text {Sc}$ collisions at CERN SPS energies with PYTHIA8/Angantyr

We study pion production in proton–proton (pp) and in central $^{7}$Be + $^{9}$Be and $^{40}\text {Ar}+ ^{45}\text {Sc}$ collisions at CERN super proton synchrotron (SPS) energies within the Angantyr model, whose pp dynamics are modeled by PYTHIA 8.303 event generator. We have tuned the parameters of the default multi-partonic interaction (MPI) mechanism in PYTHIA 8.303 to describe simultaneously the measured rapidity and transverse momentum distributions of pions in inelastic pp-collisions in the beam momentum range from 20 to 158 GeV/c. We explore the influence of the standard Lund fragmentation and thermal string models, on the $\pi ^{-}$ observables, mainly from light(er) ion beams at CERN SPS energies. The role of primary hadron rescattering (HadSc) is also discussed. We find that the PYTHIA 8.303/Angantyr model employing both pp-tuned and thermal-string model with HadSc is able to reproduce the observed $\pi ^{-}$ yields in the light(er) ion beams at the whole CERN SPS energies.