The study of the single-hadron semi-inclusive deep inelastic scattering process (SIDIS) is a rapidly developing and expanding area of inquiry in hadronic

physics, owing to the prospect of realizing a precision three-dimensional imaging

of the quark structure of the nucleon in momentum space. Measurements of the

azimuthal angular distributions of hadrons produced at large values of z = Eh=?

and...

Solenoidal Large Intensity Device (SoLID) was proposed at JLab to take the full advantage of the 12-GeV upgrade. SoLID is designed to handle high luminosities with large acceptance, which is ideal for measuring transverse momentum depended parton distribution functions (TMDs). Currently there is a highly-rated approved program focusing on the study of TMDs using semi-inclusive deep inelastic...

Semi-inclusive deep inelastic scattering (SIDIS) has proved to be an important tool for unveiling the inner structure of the core of the atom, the nucleons and their basic constituents. Azimuthal spin asymmetries in polarized SIDIS are directly related to transverse momentum dependent parton distributions (TMDs) and fragmentation functions. The TMDs allow one to probe the 3D dynamical...

The COMPASS legacy on the measurements of $g_1$ for proton and deuteron

through inclusive spin-dependent inelastic polarised-muon scattering

on longitudinally polarised NH$_3$ and $^6$LiD targets will be presented.

Results cover both deep-inelastic ($Q^2 > $ 1 (GeV/$c$)$^2$)

and non-perturbative ($Q^2 < $ 1 (GeV/$c$)$^2$) regions and a wide interval

in the Bjorken scaling variable. In the...

A new combined analysis of spin-averaged and spin-dependent PDFs reveals for the first time the *x* dependence of helicity PDFs in the *x* ~ 1 region, free from assumptions about the behavior of unpolarized PDFs that have been inherent in all previous global QCD analyses of spin data.

COMPASS final results on multiplicities of charged hadrons,

pions and kaons, produced in the deep inelastic muon scattering

off an isoscalar target will be presented. Measurements were

taken in bins of x,y and z in a wide kinematic range.

The hadron and pion data show a good agreement

with (N)LO expectations and some of the

preliminary measurements have been already incorporated

in the global...

We present an extraction of unpolarized partonic transverse momentum distributions (TMDs) from a simultaneous fit of available data measured in semi-inclusive deep inelastic scattering and in Drell-Yan processes through the production of photon and Z bosons. To connect data at different scales, we use TMD evolution at next-to-leading logarithmic accuracy. The analysis is restricted to the...

The transversity distribution was extracted for the first time from data on the transverse momentum distribution of single hadrons produced in semi-inclusive deep-inelastic scattering. The transversity was recently extracted also from the same process but leading to the inclusive production of hadron pairs in the final state. The latter analysis can be conveniently performed in the framework...

In this talk I will discuss our work (Phys.Rev.D94(2016)034014) on an improved implementation for combining transverse-momentum-dependent (TMD) factorization in semi-inclusive DIS and collinear factorization. TMD factorization is suitable for low transverse momentum physics, while collinear factorization is suitable for high transverse momenta and for a cross section integrated over transverse...

I present a first determination of a set of collinear fragmentation functions of charged pions based on the NNDPF methodology. The determination includes a wide set of single-inclusive annihilation data and is performed up to next-to-next-to-leading order accuracy in perturbative quantum chromodynamics. I discuss the results of the fits, highlighting the quality of the description of the data,...

We present a new global QCD analysis of fragmentation functions (FF) using Monte

Carlo methods. The analysis includes all existing semi-inclusive hadron

production data from electron-positron annihilation experiments including the most

resent measurements from Belle and BaBar. Preliminary analysis of combined

FF analysis with spin dependent PDF will be shown.

Deeply Virtual Compton Scattering (DVCS), in which the electron scatters from a parton inside a hadron and a high energy photon is produced as a result, is considered the golden channel for accessing Generalised Parton Distributions (GPDs), in a form of hadron tomography. One can interpret GPDs as functions relating the transverse position of partons to their longitudinal momentum and as such...

Deeply Virtual Compton Scattering (DVCS) is the easiest reaction that accesses the Generalized Parton Distributions (GPDs) of the nucleon. GPDs offer the exciting possibility of mapping the 3-D internal structure of protons and neutrons by providing a transverse image of the constituents as a function of their longitudinal momentum.

A vigorous experimental program is currently pursued at...

Wide-Angle Compton Scattering (WACS) on the proton is a powerful and under utilized probe of the transverse structure of the nucleon, which is complementary to high-$Q^{2}$ elastic electron-nucleon scattering. By demanding that all of the momentum transferred to the proton be shared among its constituents, unlike in inclusive or deeply virtual reactions, one gains access to information on the...

Key properties of the nucleon are encoded in the correlation between their longitudinal momentum and their transverse position, such as the orbital angular momentum. This correlation is expressed through Generalized Parton Distributions (GPDs), which can be understood as spatial densities at different values of the longitudinal momentum of the quark. Validation of our understanding of hard...

The HERMES experiment collected a wealth of deep-inelastic scattering data using the 27.6 GeV polarized lepton beam at HERA and various pure gas targets, both unpolarized and polarized. This allowed for a series of diverse measurements. Among them are measurements on hard exclusive meson production, which provide information on generalized parton distributions (GPDs), in a com-plementary way...

Measurements of the transverse polarization of lambda hyperons with

respect to their production plane are sensitive to the polarizing

fragmentation function $D_{1T}^{\perp \Lambda/q}$. This fragmentation

function might be part of the explanation of the significant

transverse polarization of Lambda in p+p scattering. It can also be seen

as the hadronization analogue to the Sivers function,...

The transverse spin transfer of $\Lambda$ hyperons in proton+proton collisions can provide insights into the polarized fragmentation function and the transversity distribution of the nucleon.

In this contribution, we report the first measurement of the transverse spin transfer of $\Lambda$ and $\bar{\Lambda}$ hyperons along the polarization direction of the outgoing quark in transversely...

The COMPASS experiment at CERN, as part of its programme addresses the exploration of the transverse spin structure of the nucleon by measuring spin (in)dependent azimuthal asymmetries in semi-inclusive DIS and, recently, also in Drell-Yan processes. Between 2002 and 2010 COMPASS performed a series of SIDIS measurements, using a longitudinally polarized muon beam impinging on transversely...

The Sivers function describes the correlation between the transverse spin of a nucleon and the trans-

verse motion of its partons. As such, a nonzero Sivers e?ect for gluons could be a signature of

their nonzero orbital angular momentum inside the nucleon. COMPASS has collected data of semi-

inclusive deep inelastic scattering by impinging 160 GeV=c muons on transversely polarised proton

and...

I will first try to convince you that the application of TMD factorization at small x has been well justified at tree level and NLO level. Then I will show that there is very rich polarization dependent phenomenology at small x. In particular, the small x asymptotic behavior of gluon TMDs inside an unpolarized and transversely polarized target will be discussed. The small x gluon tomograph...

Within the QCD parton model approach, the quark structure of the polarized nucleon can be parametrized in terms of spin and quark transverse momentum dependent parton distribution functions while the hadronization mechanism is described by fragmentation functions. Specific convolutions of these objects can be accessed through the measurement of longitudinal spin-dependent asymmetries in...

Investigation of GPDs and TMDs represents the major goal of the COMPASS-II program. Together, GPDs and TMDs provide the most complete description of the

partonic structure of the nucleon.

GPDs are experimentally accessible via lepton-induced exclusive reactions, in

particular DVCS and DVMP. At COMPASS, these processes are investigated using a

160 GeV high intensity muon beam and a 2.5 m long...

Generalized Parton Distributions (GPDs) provide a comprehensive description of the partonic structure of the nucleon and contain a wealth of new information. In particular, they provide a description of the nucleon as an extended object, referred to as 3-dimensional nucleon tomography, and give an access to the orbital angular momentum of quarks.

In my talk I will focus on the GPD...

We propose to study the photoproduction of a photon and a rho meson with a large invariant mass as a new and efficient probe of Generalized Patron Distributions. A full feasibility study for such a process we be presented for the example of JLab@12GeV.

We report final results for L/T separated pi0 electroproduction cross sections off the proton, the neutron and the deuteron, measured in Hall A of Jefferson Lab. We found a large transverse response for both the proton and neutron cases, pointing to a possible dominance of higher-twist transversity GPD contributions. For the first time, a flavor decomposition of the u and d quark contributions...

Generalized TMDs (GTMDs) of hadrons are the most general two-parton correlation functions. Upon certain projections several GTMDs reduce to generalized parton distributions and transverse momentum dependent parton distributions, respectively. Therefore they can be considered as partonic "mother functions". Moreover, two of the GTMDs play an important and unique role in the spin structure of...

During the past decade, the experiments of the RHIC spin program have provided critical insight into the spin structure of the nucleon, in particular, shedding light on the roles played by gluon and sea-quark helicity. In the forthcoming RHIC run, attention will be devoted to transverse-spin phenomena. Over the last decade, theoretical and experimental engagement of this oft-challenging...

Overview of transverse spin physics in the PHENIX experiment

We would like to present an overview of recent results from the PHENIX collaboration on spin physics using a transversely polarized proton beam. Several experiments have been conducted at RHIC in the past decade using such beam polarization in proton-proton collisions. Recently, polarized proton-ion collisions have also been...

Due to the non-Abelian nature of QCD, there is a prediction that quarks can become correlated across colliding protons in hadron production processes sensitive to nonperturbative transverse momentum effects. Measuring the evolution of nonperturbative transverse momentum widths as a function of the hard interaction scale can help distinguish these effects from other possibilities. ...

The sea quark contribution to nucleon spin is an important piece for a complete understanding of the nucleon spin structure. The production of $W$-bosons in longitudinally polarized $p+p$ collisions at RHIC provides a unique probe for the sea quark polarization, through the parity-violating single-spin asymmetry, $A_L$. At the STAR experiment, the leptonic decay channel $W\rightarrow e\nu$...

The production of jets from polarized p+p collisions at STAR is dominated by quark-gluon and gluon-gluon scattering. The di-jet double spin asymmetry ($A_{LL}$) is sensitive to the polarized gluon distribution ($\Delta G$). Di-jets are also advantageous because the parton momentum fraction, x, of initial partons may be reconstructed to first order from the final state measurements. Both jet...

We present the transverse single spin asymmetries $A_N$ for very forward neutrons measured by the PHENIX zero-degree calorimeters (ZDCs) in high-energy polarized proton-nucleus (p-A) collisions at RHIC. First-ever p-A data taken in the RHIC-2015 run exhibit positive and remarkably large $A_N\sim0.18$ only in p-Au collisions whereas nearly zero $A_N$ in p-Al collisions. Comparisons of these new...

We calculate the leading order in $α_s$ QCD amplitude for exclusive neutrino and antineutrino production of a D pseudoscalar charmed meson on an unpolarized nucleon. We work in the framework of the collinear QCD approach where generalized parton distributions (GPDs) factorize from perturbatively calculable coefficient functions. We include both $O(m_c)$ terms in the coefficient functions

and...

Wigner distributions give a three dimensional picture of the quarks and gluons in a nucleon, and are related to the generalzed transverse momentum dependent parton distributions (GTMDs). These also give the orbital angular momentum and the spin-orbit correlations of the quarks and gluons. We calculate the Wigner distributions and GTMDs for a simple spin 1/2 composite state, namely a quark...

Hadron tomography can be investigated by three-dimensional structure functions

such as generalized parton distributions (GPDs),

transverse-momentum-dependent parton distribution (TMDs),

and generalized distribution amplitudes (GDAs).

Here, we extract the GDAs, which are $s$-$t$ crossed quantities of

the GPDs, from cross-section measurements of

hadron-pair production process $\gamma \gamma^*...

Generalized parton distributions (GPDs) encoding multidimensional information of hadron partonic structure appear as the building blocks in a factorized description of hard exclusive reactions. The nucleon GPDs have been accessed by deeply virtual Compton scattering and deeply virtual meson production with lepton beam. A complementary probe with hadron beam is the exclusive pion-induced...

Longitudinal double spin asymmetry $A_{LL}$ of hadron, jet and direct photon in p+p collisions at the Relativistic Heavy Ion Collider (RHIC) is sensitive to the gluon spin at leading order. Unlike hadrons and jet, direct photon production provides clean access to the polarized gluon distribution since there is involved in this process. However, small direct photon cross section compared to...

In SIDIS, the formalism of TMDs corresponds to a specific partonic picture, in which the observed hadron is produced by the struck quark, via

*current fragmentation*. For phenomenological applications, it is of prime importance to identify the kinematical region in which

the corresponding factorization theorem can safely be applied. In this talk I will discuss a criterion to determine this...

The single transverse spin asymmetries in semi-inclusive DIS, with $P_{h\perp}$, i.e., the transverse momentum of the final detected hadron integrated over, are studied. At twist-3 level, it is found that the hadronic tensor at tree level contains two parts: the first one is non-derivative part, which is proportional to $\delta^2(P_{h\perp})$; the second one is derivative part, which is...

Chiral Even and Odd Generalized Parton Distributions (GPDs) for Valence Quarks were obtained in a "flexible" spectator model. These were constrained by nucleon form factors, PDFs, earlier Deeply Virtual Compton Scattering data and electroproduction of pion data. A 3-d picture of the quark distributions within the nucleon emerges. The model has been extended to include sea quarks and gluon...