Detecting correlated di-hadron pairs: about the extraction of transversity and beyond

TL;DR

This paper reviews recent progress in extracting the transversity parton distribution and proton tensor charge from di-hadron production data, highlighting flavor separation and potential new correlations related to QCD topology.

Contribution

It introduces a collinear factorization approach using di-hadron fragmentation functions for transversity extraction and discusses novel azimuthal correlations linked to QCD topological effects.

Findings

Flavor-separated valence transversity distributions obtained from HERMES and COMPASS data.

Use of di-hadron fragmentation functions from e+e- annihilation analyses.

Discussion of potential parity-odd correlations from topologically nontrivial QCD backgrounds.

Abstract

We summarize the latest achievements about the extraction of the transversity parton distribution and proton tensor charge based on an analysis of pion-pair production in deep-inelastic scattering off transversely polarized targets. Recently released data for proton and deuteron targets by HERMES and COMPASS allow for a flavor separation of the valence components of transversity. At variance with the Collins effect, this extraction is performed in the framework of collinear factorization and relies on di-hadron fragmentation functions. The latter have been taken from the first recent analysis of the semi-inclusive production of two pion pairs in back-to-back jets in e+e- annihilation. We also comment on the possibility of isolating new azimuthally asymmetric correlations of opposite pion pairs, which could arise when a fragmenting quark crosses parity-odd domains localized in Minkowski space-time and induced by the topologically nontrivial QCD background (the so-called \theta\ vacuum).