Assessing the sensitivity of energy-energy correlations in e+e− annihilation to TMD dynamics

A bstract 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 (N 4 LL) 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 α s .