Transverse-spin and transverse-momentum effects in high-energy processes

Abstract

The state of the art concerning transverse-spin and transverse-momentum phenomena\ud in hard hadronic reactions is reviewed. An account is given of single-spin and azimuthal\ud asymmetries in semi-inclusive deep inelastic scattering, e+e− annihilation, Drell–Yan\ud production, and hadroproduction. The ongoing experiments and the main theoretical\ud frameworks are described in the first part of the paper. The second part is devoted to the\ud experimental findings and their phenomenological interpretations. A brief discussion of\ud the perspectives of future measurements is finally presented

Origin of model relations among transverse-momentum dependent parton distributions

“…The total orbital angular momentum of a given component c à is given by the expression ' z ¼ à À with Ã; ¼ AE 1 2 . The corresponding LCWF in the canonical-spin basis is defined through…”

“…TMDs typically give rise to spin and azimuthal asymmetries in, for instance, semi-inclusive deep inelastic scattering and Drell-Yan processes, and significant efforts have already been devoted to measure these observables (see, e.g., Ref. [1] for a recent review). However, the extraction of TMDs from experimental data is a quite difficult task and needs educated Ansätze for fits of TMD parametrizations.…”

Phenomenological analysis of azimuthal asymmetries in unpolarized semi-inclusive deep inelastic scattering

“…Focusing on SIDIS processes, while at large momentum transfer Q and large P T (the transverse momentum of the produced hadron), the azimuthal asymmetries are perturbatively generated by gluon radiation, at small P T , P T ≪ Q, they can arise from the intrinsic motion of quarks [3][4][5][6] (for a review, see Ref. [7]). In the latter regime, the so-called transverse-momentum-dependent (TMD) factorization applies, and the SIDIS structure functions (in the current fragmentation region) can be written as transversemomentum convolutions of TMD distribution and fragmentation functions [8].…”

The multidimensional nucleon structure

“…During the past two decades, a lot of attention has been paid to generalized parton distributions (GPDs) [1][2][3][4][5][6][7] and to transverse-momentum dependent parton distributions (TMDs) [8][9][10][11][12]. Those objects are of particular interest because they describe the three-dimensional parton structure of hadronsthe distribution of the parton's longitudinal momentum and transverse position in the case of GPDs, and the distribution of the parton's longitudinal momentum and transverse momentum in the case of TMDs.…”