We study the cross section for one-particle inclusive deep inelastic scattering off the nucleon for low transverse momentum of the detected hadron. We decompose the cross section in terms of structure functions and calculate them at tree level in terms of transverse-momentum-dependent parton distribution and fragmentation functions. Our results are complete in the one-photon exchange approximation at leading and first subleading twist accuracy, with both beam and target polarization.

The fully unintegrated, off-diagonal quark-quark correlator for a spin-1/2 hadron is parameterized in terms of so-called generalized parton correlation functions. Such objects, in particular, can be considered as mother distributions of generalized parton distributions on the one hand and transverse momentum dependent parton distributions on the other. Therefore, our study provides new, model-independent insights into the recently proposed nontrivial relations between generalized and transverse momentum dependent parton distributions. We find that none of these relations can be promoted to a model-independent status. As a by-product we obtain the first complete classification of generalized parton distributions beyond leading twist. The present paper is a natural extension of our previous corresponding analysis for spin-0 hadrons.

In this paper we present a comprehensive formalism for dilepton production from the collision of two polarized spin-1 2 hadrons by identifying the general angular distribution of the cross section in combination with a complete set of structure functions. The various structure functions are computed in the parton model approximation where we mainly consider the case when the transverse momentum of the dilepton pair is much smaller than its invariant mass. In this kinematical region dilepton production can be described in terms of transverse momentum dependent parton distributions.

The naive time-reversal-odd (''T-odd'') parton distribution h ? 1 , the so-called Boer-Mulders function, for both up (u) and down (d) quarks is considered in the diquark spectator model. While the results of different articles in the literature suggest that the signs of the Boer-Mulders function in semi-inclusive deep inelastic scattering (SIDIS) for both flavors u and d are the same and negative, a previous calculation in the diquark spectator model found that h ?ðuÞ 1 and h ?ðdÞ 1 have different signs. The flavor dependence is of significance for the analysis of the azimuthal cosð2Þ asymmetries in unpolarized SIDIS and Drell-Yan processes, as well as for the overall physical understanding of the distribution of transversely polarized quarks in unpolarized nucleons. We find substantial differences with previous work. In particular, we obtain half and first moments of the Boer-Mulders function that are negative over the full range in Bjorken x for both the u and d quarks. In conjunction with the Collins function, we then predict the cosð2Þ azimuthal asymmetry for þ and À in this framework. We also find that the Sivers u and d quarks are negative and positive, respectively. As a by-product of the formalism, we calculate the chiral-odd but ''T-even'' function h ?1L , which allows us to present a prediction for the single-spin asymmetry A sinð2Þ UL for a longitudinally polarized target in SIDIS.

We argue that the study of heavy quarkonia, in particular that of Υ, produced back to back with an isolated photon in pp collisions at the LHC is the best -and currently unique-way to access the distribution of both the transverse momentum and the polarization of the gluon in an unpolarized proton. These encode fundamental information on the dynamics of QCD. We have derived analytical expressions for various transverse-momentum distributions which can be measured at the LHC and which allow for a direct extraction of the aforementioned quantities. To assess the feasibility of such measurements, we have evaluated the expected yields and the relevant transverse-momentum distributions for different models of the gluon dynamics inside a proton.