Experimental results on TMDs

Abstract

QCD factorisation for semi-inclusive deep inelastic scattering at low transverse momentum in the current-fragmentation region has been established recently, providing a rigorous basis to study the Transverse Momentum Dependent distribution and fragmentation functions (TMDs) of partons from Semi-Inclusive DIS data using different spin-dependent and spin-independent observables. The main focus of the experiments were the measurements of various single-and double-spin asymmetries in hadron electro-production (ep ↑ → ehX) with unpolarised, longitudinally and transversely polarised targets. The joint use of a longitudinally polarised beam and longitudinally and transversely polarised targets allowed to measure double-spin asymmetries (DSA) related to leading-twist distribution functions describing the transverse momentum distribution of longitudinally and transversely polarised quarks in a longitudinally and transversely polarised nucleons (helicity and worm-gear TMDs). The single-spin asymmetries (SSA) measured with transversely polarised targets, provided access to specific leading-twist parton distribution functions: the transversity, the Sivers function and the so-called "pretzelosity" function. In this review we present the current status and some future measurements of TMDs worldwide.

Mapping the kinematical regimes of semi-inclusive deep inelastic scattering

“…(8.14) is negligible, so R 1 is the first of the R 0 -R 3 that we will consider here. [6,36,37], are applied in each case. The values of z N /z h , for pion production (upper panels) and kaon production (lower panels) are obtained using Eq.…”

“…Deep inelastic scattering (DIS), and especially semi-inclusive deep inelastic scattering (SIDIS) are headlining processes in most programs to the study of partonic (quark and gluon) degrees of freedom. It is a cornerstone process of, for example, the Jefferson Lab 12 GeV program to study partonic structure in hadrons, and is one of the important processes for study in a possible future Electron-Ion Collider (EIC) [1][2][3][4][5][6]. Interest in SIDIS arises from a variety of considerations.…”

“…By "moderate-to-low Q," we will mean SIDIS measurements with Q roughly between 1 GeV and 3 GeV and Bjorken-x Bj not too far below the valence region. This includes JLab 6 GeV and 12 GeV SIDIS cross section measurements [1,4,6].…”

Review of TMD Measurements

“…After the seminal work of HERMES [10] showing for the first time non-zero azimuthal asymmetries generated by TMDs in SIDIS reactions, the study of this effects has been spread world-wide over many facilities and different reactions (hadron-hadron interactions, e + e − and Drell-Yan annihilation). Several evidences have been collected of the existence of non-trivial correlations among the quark degrees of freedoms [11]. These studies has been recognized as an important topic for many upcoming new facilities.…”

Transverse–Spin Quark Distributions from Asymmetry Data and Symmetry Arguments

“…The investigation of the transverse-spin structure of nucleons has been an extremely active research area of hadronic physics in the past two decades [1,2]. Single-spin asymmetries in leptoproduction of hadrons from a transversely polarized target, N ↑ → hX, have been discovered and measured by various experiments (for a review, see, e.g., in [3]), and represent the primary way to access the transverse-spin distributions of quarks.…”