Collins-type Energy-Energy Correlators and Nucleon Structure

TL;DR

This paper introduces azimuthal angle dependent Energy-Energy Correlators (EEC) to probe the 3D spin structure of nucleons in high-energy scattering experiments, linking jet functions to TMD and Collins fragmentation functions.

Contribution

It generalizes the EEC to include azimuthal dependence and demonstrates its sensitivity to nucleon structure and fragmentation functions in $e^+e^-$ and SIDIS processes.

Findings

Azimuthal EEC correlators are sensitive to unpolarized and Collins-type jet functions.

The new observables provide access to the 3D spin-dependent nucleon structure.

Connections established between EEC jet functions and TMD/Collins fragmentation functions.

Abstract

We generalize the conventional Energy-Energy Correlator (EEC) to include the azimuthal angle dependence, so to define azimuthal angle dependent EEC observables. We study this new EEC observable in $e^+e^-$ and semi-inclusive deep inelastic scattering (SIDIS). In the back-to-back region, we find that the azimuthal angle dependent EEC is sensitive to both the unpolarized EEC jet function and a Collins-type EEC jet function. While the unpolarized EEC jet function is related to the unpolarized transverse momentum dependent (TMD) fragmentation function, the Collins-type EEC jet function is connected with the Collins fragmentation function. We further demonstrate how the new observables allow us to access to the 3D structure of nucleons, especially the spin-dependent ones.