Speaker
Description
Recent experimental observations of collective-like phenomena in small collision systems, such as pp collisions, have challenged traditional paradigms and highlighted the critical role of initial-state geometry and its fluctuations. In particular, longitudinal decorrelations serve as a powerful probe of the three-dimensional initial-state structure and longitudinal dynamics of the collision system. In this work, we investigate longitudinal decorrelations in pp collisions at 13 TeV using a modified version of the AMPT model in which the conventional nucleon profile is replaced by a sub-nucleonic structure consisting of localized constituent-quark hotspots. This additional spatial granularity generates substantially stronger event-by-event fluctuations in the initial geometry. We find that incorporating three constituent-quark hotspots per nucleon significantly enhances the magnitude of longitudinal decorrelations compared with conventional point-like nucleon initial conditions. By studying the evolution from the fluctuating initial state to the final-state partonic dynamics within AMPT, we further investigate how initial-state sub-nucleon structure influences longitudinal correlations and the emergence of collectivity in small systems. These results demonstrate the importance of sub-nucleon degrees of freedom for describing longitudinal dynamics in pp collisions and provide new constraints on models of the initial state in small collision systems.
