Utilizing high-p⊥ theory and data to constrain the initial stages of quark-gluon plasma

The scarce knowledge of the initial stages of quark-gluon plasma before the thermalization is mostly inferred through the low-[Formula: see text] sector. We propose a complementary approach in this report — the use of high-[Formula: see text] probes’ energy loss. We study the effects of four commonly assumed initial stages, whose temperature profiles differ only before the thermalization, on high-[Formula: see text][Formula: see text] and [Formula: see text] predictions. The predictions are based on our Dynamical Radiative and Elastic ENergy-loss Approach (DREENA) framework. We report insensitivity of [Formula: see text] to the initial stages, making it unable to distinguish between different cases. [Formula: see text] displays sensitivity to the presumed initial stages, but current experimental precision does not allow resolution between these cases. We further revise the commonly accepted procedure of fitting the energy loss parameters, for each individual initial stage, to the measured [Formula: see text]. We show that the sensitivity of [Formula: see text] to various initial stages obtained through such procedure is mostly a consequence of fitting procedure, which may obscure the physical interpretations. Overall, the simultaneous study of high-[Formula: see text] observables, with unchanged energy loss parametrization and restrained temperature profiles, is crucial for future constraints on initial stages.