Impact of baryon suppression and shadowing effects on identified hadron spectra in p + C collisions at 31 GeV/ c within the PYTHIA8 Angantyr framework

Abstract We present a comparative study of identified hadron production—protons, charged pions, and charged kaons—in proton–carbon ( p + C) interactions at 31 GeV/ c , analyzed across angular intervals θ = 0–140 mrad for protons and charged pions, and θ = 0–180 mrad for charged kaons. The analysis is based on a series of systematically configured simulations using the Pythia 8 event generator with Angantyr modeling, including several targeted modifications aimed at improving agreement with experimental data from the NA61/SHINE collaboration. We show that the default Angantyr setup tends to overestimate proton yields at mid-to-large angles ( θ = 40–140 mrad) in the low-momentum region ( p = 2–10 GeV/ c ), while underestimating forward-angle yields at higher momentum ( p > 10 GeV/ c ). It also exhibits an anomalous beam-like enhancement near p ≈ 31 GeV/ c at forward angles ( θ = 0–40 mrad). To address these discrepancies, we implemented a modified subcollision model with Angantyr, enhanced with a constant suppression scheme for primary non-diffractive, single diffractive, double diffractive, and elastic nucleon–nucleon subcollisions. This approach phenomenologically emulates coherence and nuclear shadowing effects, reducing the probability of multiple independent subcollisions in the nuclear environment. In parallel, we employed a thermal string fragmentation model that suppresses the B ¯ M B channel in baryon production, yielding a more localized and physically consistent baryon spectrum. When combined with hadronic rescattering, the full model configuration reproduces the detailed structure of proton momentum spectra, enhances forward-angle yields ( θ = 0–40 mrad), and suppresses excess production at larger angles ( θ ≥ 40 mrad). Similar improvements are observed for π ± and K ± spectra. Overall, our results demonstrate that incorporating subcollision suppression, thermal hadronization, and final-state rescattering significantly improves the predictive power of Pythia 8 for p + C collisions at SPS energies.