Eur. Phys. J. A (2016) 52: 155
https://doi.org/10.1140/epja/i2016-16155-5

Review

Di-hadron fragmentation and mapping of the nucleon structure

¹ INFN, Laboratori Nazionali di Frascati, Via Enrico Fermi 40, 00044, Frascati, Italy
² INFN, Sezione di Pavia, via Bassi 6, I-27100, Pavia, Italy

^* e-mail: silvia.pisano@lnf.infn.it

Received: 6 November 2015
Accepted: 17 November 2015
Published online: 17 June 2016

Abstract

The fragmentation of a colored parton directly into a pair of colorless hadrons is a non-perturbative mechanism that offers important insights into the nucleon structure. Di-hadron fragmentation functions can be extracted from semi-inclusive electron-positron annihilation data. They also appear in observables describing the semi-inclusive production of two hadrons in deep-inelastic scattering of leptons off nucleons or in hadron-hadron collisions. When a target nucleon is transversely polarized, a specific chiral-odd di-hadron fragmentation function can be used as the analyzer of the net density of transversely polarized quarks in a transversely polarized nucleon, the so-called transversity distribution. The latter can be extracted through suitable single-spin asymmetries in the framework of collinear factorization, thus in a much simpler framework with respect to the traditional one in single-hadron fragmentation. At subleading twist, the same chiral-odd di-hadron fragmentation function provides the cleanest access to the poorly known twist-3 parton distribution e(x) , which is intimately related to the mechanism of dynamical chiral symmetry breaking in QCD. When sensitive to details of transverse-momentum dynamics of partons, the di-hadron fragmentation functions for a longitudinally polarized quark can be connected to the longitudinal jet handedness to explore possible effects due to CP -violation of the QCD vacuum. In this review, we outline the formalism of di-hadron fragmentation functions, we discuss different observables where they appear and we present measurements and future worldwide plans.