We perform a comprehensive Bayesian analysis of Au $+$ Au collision data at 1.23 GeV/nucleon using an isospin-dependent Boltzmann-Uehling-Uhlenbeck transport model that incorporates a momentum-dependent mean field and medium-modified baryon-baryon cross sections. The model parameters are calibrated to empirical properties of nuclear matter at saturation density, with particular attention to variations in the incompressibility $K_0$. Within a Bayesian statistical framework and using a Gaussian Process emulator, we simultaneously extract constraints on the incompressibility $K_0$ and the in-medium baryon-baryon scattering modification factor $X$ by systematically comparing model predictions with HADES measurements of proton collective flow, including the slopes ($F_1$ and $F_3$) of directed and triangular flow, as well as elliptic ($v_2$) and quadrupole ($v_4$) flow observables. We find that the extracted incompressibility favors relatively small values, indicating a soft nuclear equation of state, while the inferred average $X$ values fall at $0.9–1.0$, suggesting mild suppression of baryon-baryon cross sections in the medium. Furthermore, we demonstrate that transport models employing momentum-independent mean fields require stiffer equations of state and stronger in-medium corrections to reproduce the same observables. These results highlight the critical role of momentum dependence in the mean field and its interplay with in-medium scattering in constraining the properties of dense nuclear matter from heavy ion collisions.

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• Equations of state of nuclear matter
• Low & intermediate energy heavy-ion reactions
• Nuclear forces
• Bayesian networks
• Bayesian methods