The high-energy behavior of tree-level scattering in finite-temperature QCD: estimates of theoretical systematic uncertainty in jet-medium Monte Carlo simulations

We examine the behavior of tree-level scattering in thermal QCD at high energies and find significant deviations away from the commonly used approximations [Phys. Rev. D 44, 1298 (1991), Phys. Rev. D 44, R2625 (1991), Phys. Rev. D.77, 014015 (2008), Phys. Rev. D. 77.114017 (2008)]. These deviations in the scattering rate also affect jet-medium transport coefficients at the partonic level, leading to a different kinematic dependence of the transverse momentum broadening per unit length $\widehat{q}$. As scattering rates and $\widehat{q}$ are used by large-scale Monte Carlo simulations of jets in the quark-gluon plasma (QGP), such as [Phys. Rev. C 111,054913 (2025)], current constraints on $\widehat{q}$ are biased owing to the approximations used therein. Besides theoretically improving $\widehat{q}$, the differences between the $\widehat{q}$ herein and the approximate $\widehat{q}$ used in jet Monte Carlo simulations are used to construct a theoretical systematic uncertainty, which in turn can be employed to devise a covariance matrix for $\widehat{q}$ and enables updating the uncertainty bands on $\widehat{q}$ obtained by Bayesian analysis.