Constraining the Nucleon Size with Relativistic Nuclear Collisions

The notion of the size of nucleons and their constituents plays a pivotal role in the current paradigm of the formation and the fluctuations of the quark-gluon plasma produced in high-energy nuclear collision experiments. We report on state-of-the-art hydrodynamic results showing that the correlation between anisotropic flow v2n and the mean transverse momentum of hadrons [pt] possesses a unique sensitivity to the nucleon size in off-central heavy-ion collisions. We argue that existing experimental measurements of this observable support a picture where the relevant length scale characterizing the colliding nucleons is of order 0.5 fm or smaller, and we discuss the broad implications of this finding for future global Bayesian analyses aimed at extracting initial-state and medium properties from nucleus-nucleus collision data, including v2n-[pt] correlations. Determinations of the nucleon size in heavy-ion collisions will provide a solid independent constraint on the initial state of small system collisions and will establish a deep connection between collective flow data in nucleus-nucleus experiments and data on deep inelastic scattering on protons and nuclei.

Automated summary

The size of nucleons and their constituents are crucial in understanding the formation and fluctuations of the quark-gluon plasma produced in high-energy nuclear collision experiments. Recent hydrodynamic results show that the correlation between anisotropic flow and the mean transverse momentum of hadrons has a unique sensitivity to the nucleon size in off-central heavy-ion collisions. This finding has broad implications for future analyses of nucleus-nucleus collision data and deep inelastic scattering on protons and nuclei.