We critically examine the back-to-back limit of the energy-energy correlation (EEC) in e+e− annihilation as a potential source of information on the Collins-Soper kernel and the strong coupling constant. The analysis is performed within the framework of transverse momentum dependent (TMD) factorization at next-to-next-to-next-to-next-to-leading logarithmic (N4LL) accuracy, using a global fit to all available experimental data. Contrary to previous claims, we demonstrate that the current data do not provide meaningful constraints on either the Collins-Soper kernel or αs.
@article{arxiv.2507.17478,
title = {Assessing the sensitivity of Energy-Energy Correlations in $e^+e^-$ annihilation to TMD dynamics},
author = {Alejandro Bris Cuerpo and Ignazio Scimemi and Alexey Vladimirov},
journal= {arXiv preprint arXiv:2507.17478},
year = {2025}
}