Spectral analysis of gluonic pole matrix elements for fragmentation

Understand

The non-vanishing of gluonic pole matrix elements can explain the appearance of single spin asymmetries in high-energy scattering processes.

• We use a spectator framework approach to investigate the spectral properties of quark-quark-gluon correlators and use this to study gluonic pole matrix elements.
• Such matrix elements appear in principle both for distribution functions such as the Sivers function and fragmentation functions such as the Collins function.
• We find that for a large class of spectator models, the contribution of the gluonic pole matrix element in fragmentation functions vanishes.