Abstract
The study of the quantum phase-space distribution of quarks and gluons inside nucleons in terms of TMDs and GPDs has become, in the last decade, a cutting-edge research field in hadron physics. These non-perturbative objects, respectively measurable in semi-inclusive deep-inelastic scattering and exclusive processes, allow to obtain 3-dimensional representations of the nucleon in the momentum and spatial coordinates as well as indirect insights into the still unknown parton orbital angular momentum. The HERMES experiment at HERA has been a precursor in this field. A selection of HERMES results sensitive to both TMDs and GPDs is presented.
Highlights
The study of the quantum phase-space distribution of quarks and gluons inside nucleons in terms of Transverse Momentum Dependent parton distribution function (PDF) (TMDs) and Generalized Parton Distributions (GPDs) has become, in the last decade, a cutting-edge research field in hadron physics
TMDs and GPDs allow for complementary descriptions of the nucleon in three dimensions, spanned by the quark’s longitudinal momentum and, respectively, by its transverse momentum components and transverse spatial coordinates
TMDs and GPDs can be accessed through the analysis of specific azimuthal asymmetries measured, respectively, in semi-inclusive DIS (SIDIS) and hard exclusive processes, such as hard lepto-production of real photons or mesons
Summary
The study of the quantum phase-space distribution of quarks and gluons inside nucleons in terms of TMDs and GPDs has become, in the last decade, a cutting-edge research field in hadron physics. The HERMES experiment provided first evidences of a non-zero transverse spin distribution of up and down quarks, described by the transversity PDF h1(x), through the measurement of specific azimuthal asymmetries in the production of π+ and π− (the so-called Collins effect) in semi-inclusive DIS (SIDIS) measurements off a transversely polarized hydrogen target [2].
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