### Conveners

#### Transverse Momentum Structure (TMD): Chair: Alessandro Bacchetta

- Shinsuke Yoshida (Niigata University)
- Ralf Seidl (RIKEN)
- Michela Chiosso (University of Torino and INFN)

#### Transverse Momentum Structure (TMD): Chair: Pasquale di Nezza

- Michela Chiosso (University of Torino and INFN)
- Shinsuke Yoshida (South China Normal University)
- Ralf Seidl (RIKEN)

#### Transverse Momentum Structure (TMD): Chair: Michaela Chiosso

- Michela Chiosso (University of Torino and INFN)
- Shinsuke Yoshida (South China Normal University)
- Ralf Seidl (RIKEN)

#### Transverse Momentum Structure (TMD): Chair: Zuo-Tang Liang

- Michela Chiosso (University of Torino and INFN)
- Shinsuke Yoshida (South China Normal University)
- Ralf Seidl (RIKEN)

#### Transverse Momentum Structure (TMD): Chair: Shinsuke Yoshida

- Michela Chiosso (University of Torino and INFN)
- Shinsuke Yoshida (South China Normal University)
- Ralf Seidl (RIKEN)

#### Transverse Momentum Structure (TMD): Chair: Leonard Gamberg

- Shinsuke Yoshida (South China Normal University)
- Michela Chiosso (University of Torino and INFN)
- Ralf Seidl (RIKEN)

#### Transverse Momentum Structure (TMD): Chair: Ralf Seidl

- Michela Chiosso (University of Torino and INFN)
- Ralf Seidl (RIKEN)
- Shinsuke Yoshida (South China Normal University)

#### Transverse Momentum Structure (TMD): Chair: Alexei Prokudin

- Shinsuke Yoshida (South China Normal University)
- Ralf Seidl (RIKEN)
- Michela Chiosso (University of Torino and INFN)

As part of the investigation programme of the transverse spin and transverse momentum structure of the nucleon in semi-inclusive DIS processes, COMPASS has measured several transverse momentum distributions of the final state hadrons in DIS of 160 GeV/c muons off unpolarised targets.

Recently transverse momentum distributions were obtained by scattering the muons off an isoscalar target...

A comprehensive set of azimuthal single-spin and double-spin asymmetries in semi-inclusive leptoproduction of pions, charged kaons, protons, and antiprotons from transversely polarized protons is presented. These asymmetries include the previously published \hermes results on Collins and Sivers asymmetries, the analysis of which has been extended to include protons and antiprotons and also to...

In QCD the momentum and spin structure of the nucleon explored in hard-scattering reactions is described in terms of Transverse Momentum Dependent Parton Distribution Functions (TMD PDFs). The PDFs were studied primarily in the collinear approximation, until it was demonstrated that the intrinsic transverse motion of partons plays an important role.

In Semi-Inclusive Deep Inelastic Scattering...

The study of the partonic and spin structure of the nucleon, using semi-inclusive measurements of hadron muoproduction in Deep Inelastic Scattering (DIS), is one of the main objectives of the COMPASS experiment at CERN. Within the QCD parton model approach, the nucleon structure in DIS can be parametrized in terms of Transverse Momentum Dependent (TMD) Parton Distribution Functions (PDFs),...

The HERMES experiment has collected a wealth of data using the 27.6 GeV polarized HERA lepton beam and various polarized and unpolarized gaseous targets. This allows for a series of unique measurements of observables sensitive to the multidimensional (spin) structure of the nucleon, in particular semi-inclusive deep-inelastic scattering (SIDIS) measurements, for which the HERMES dual-radiator...

Electron-positron annihilation into hadrons is one of the fundamental tools for studying non-perturbative QCD effects. Fragmentation functions, describing the formation of hadrons from partons, are an indispensable tool in the interpretation of hadron-production data, e.g., in the investigation of nucleon structure via semi-inclusive deep-inelastic scattering. The cleanest process to access...

We make a systemic study on the longitudinal polarization and two transverse polarizations of the $\Lambda$ hyperons produced in unpolarized SIDIS and $e^+e^-$ annihilation.

Recently, Belle collaboration measured the transverse polarization ($P_N$) of $\Lambda$ hyperons in $e^+e^-$ annihilation [1], which inspired three parameterizations of the $D_{1T}^\perp (z,p_T)$ fragmentation function...

We present the complete structure of the azimuthal dependences and polarization observables for two-hadron production in $e^+e^-$ annihilation processes within a TMD approach adopting the helicity formalism. The leading-twist quark and gluon TMD fragmentation functions (FFs) for spin-1/2 hadrons, with their properties and their probabilistic interpretation, are fully accounted for.

The...

Data from the Belle Collaboration for associated production (with a light unpolarized hadron) and single-inclusive production of transversely polarized $\Lambda$-hyperons in $e^+e^-$ annihilation processes allowed to extract, for the first time, the $\Lambda$ polarizing fragmentation function, by adopting a simplified TMD approach.

Recent theoretical developments on the computation of cross...

COMPASS is a fixed-target high energy physics experiment located at the M2 beamline of the Super Proton Synchrotron at CERN. The study of the spin structure of the nucleon by measuring nucleon spin (in)dependent azimuthal asymmetries in Drell-Yan process is one of the main topics of the phase-II research programme of the experiment.

In 2015 and 2018 COMPASS performed Drell-Yan measurements...

We perform explorative analyses of the 3D gluon content of the proton via a study of polarized T-odd gluon TMDs at leading twist, calculated in a spectator model for the parent nucleon. Our approach encodes a flexible parameterization for the spectator-mass density, suited to describe both moderate and small-x effects. All these prospective developments are relevant in the investigation of the...

We study the polarization of 𝐽/𝜓 mesons produced in semi-inclusive, deep-inelastic electron-proton scattering in different reference frames at the EIC energies. At low transverse momentum, we propose factorized expressions in terms of transverse momentum dependent gluon distributions and shape functions. In particular, we show that the distribution of linearly polarized gluons can, in...

We study the Sivers azimuthal asymmetry for $J/\psi$ production in semi-inclusive deeply inelastic scattering, with the aim of gaining information on the poorly known gluon Sivers function. We concentrate on the $J/\psi$ low transverse momentum region, adopting the transverse-momentum dependent generalized parton model (GPM), and its color gauge invariant extension (CGI-GPM), which includes...

The tensor polarization of virtual photons revealed in angular distributions of Drell-Yan processes may be described in simple geometric model.

The results are compared with collier and fixed target data. The model compatibility with pQCD is discussed.

The contribution as a background for TMDs (in particular, Boer-Muders distribution) studies is considered

We review the recent progress on the extraction of unpolarized TMD PDFs and TMD FFs from global data of Semi-Inclusive Deep-Inelastic Scattering, Drell-Yan and Z boson production. In particular, we address the tension between the low-energy SIDIS data and the theory predictions, and explore the impact of the very precise LHC data on the fit results.

We explain possible transverse-momentum-dependent parton distribution functions (TMDs) for spin-1 hadrons up to twist 4 by decomposing a quark correlation function with the conditions of the Hermiticity and parity invariance [1]. In the TMDs, there exist time-reversal-odd functions in addition to the time-reversal-even ones. We showed that 40 TMDs exist in the tensor-polarized spin-1 hadron in...

Semi-inclusive deep inelastic scattering (SIDIS) is one of the key processes to extract transverse momentum dependent parton distributions (TMDs). An advantage of electrons is that they are much cleaner probes of nucleon structure than hadron beams, but, at the same time, electron scattering at large momentum transfer can be a source of considerable photon radiation, which can significantly...

We propose an estimate of cos(2$\phi$) azimuthal asymmetry in $J/\psi$ electroproduction, in an unpolarized electron-proton scattering process. We have used a non-relativistic QCD (NRQCD) framework for the $J/\psi$ production rate. Within the kinematical range of the proposed Electron-Ion Collider (EIC), this can investigate the linearly polarised gluon distribution in the unpolarized proton....

We discuss twist-3 gluon fragmentation function (FF) contribution to the polarized hyperon production in unpolarized pp collisions. The final formula for the LO cross section is presented. We emphasize the importance of the Lorentz invariance relations and the QCD equation-of-motion relations among the twist-3 gluon FFs to guarantee the frame independence of the twist-3 cross section. This...

We study the transverse polarization of hyperons produced

in semi-inclusive deep inelastic scattering, $ep \to e\Lambda^{\uparrow}X$,

in the collinear twist-3 factorization. This process receives three types of

twist-3 contributions: (i) twist-3 distribution in the initial proton combined

with the transversity fragmentation function (FF) for the hyperon,

(ii) Twist-3 quark FFs for the...

The beam-spin induced polarization of Λ and anti-Λ hyperons produced in deep-inelastic scattering of longitudinally polarized positrons from unpolarized nucleons has been investigated by the HERMES experiment at a positron beam energy of 27.6 GeV. Here, preliminary results are reported from data taken in the years

1999 to 2007, including in particular the two high-luminosity periods of 2006...

The transverse spin transfer, $D_{TT}$, of $\Lambda$ and $\overline{\Lambda}$ hyperons in $p$+$p$ collisions is expected to be sensitive to the $s$ and $\bar{s}$ quark transversity distributions in the proton and to the transversely polarized fragmetation functions. The STAR experiment has published the first measurement of the transverse spin transfer of $\Lambda$ and $\overline{\Lambda}$...

The Lund String Fragmentation Model, widely used in Monte Carlo generators of jets, is extended to include the quark spin as a full quantum-mechanical degree of freedom, described by Pauli spinors. Such a model is needed to describe consistently the azimuthal asymmetries in jets from polarized quarks, like the Collins effect, di-hadron asymmetry and jet handedness.

The model is formulated in...

The recursive quantum mechanical string+3P0 model of polarized quark

fragmentation with pseudoscalar and vector meson production developed recently

has been implemented for the first time in a stand alone Monte Carlo program.

The program allows for a detailed study of the still unknown Collins effect for

vector meson production and of the effects of vector meson decays on the

Collins and...

In this talk, I will introduce our recent study on the probing transverse momentum-dependent gluon Sivers function in open heavy flavor quark production at the future EIC. We derive the theoretical framework to calculate heavy-quark pair production in the small transverse momentum region. Based on the factorization and resummation formula, we resum large logarithms in the small qT region and...

Understanding the internal spin structure of the nucleon still remains a challenge in strong interaction physics. Transversity, which describes the transverse spin structure of quarks in a transversely polarized proton, is still poorly constrained by experimental data. Since it is chiral-odd, it can only be accessed through channels that couple to other chiral-odd distributions, like the...

Spin asymmetries provide a wide range of insights into nucleon structure and

hadronization. Recent measurements of beam spin asymmetries of $\pi^+\pi^-$

dihadrons from SIDIS at CLAS12 provide the first empirical evidence of a nonzero

$G_1^\perp$, the parton helicity-dependent dihadron fragmentation function

(DiFF) encoding spin-momentum correlations in hadronization. These...

At the leading twist, the transversity distribution function, $h^{q}_{1}(x)$, where $x$ is the longitudinal momentum fraction of the proton carried by quark $q$, encodes the transverse spin structure of the proton. Extraction of it is difficult because of its chiral-odd nature. However, it can be coupled to a spin-dependent interference fragmentation function, leading to experimentally...

Very forward neutron production cross sections in proton proton collisions are well described by a one pion exchange (OPE) mechanism. However, the simple OPE model alone was not able to explain the large transverse single spin asymmetry ($A_{N}$) that was discovered at RHIC in polarized proton proton collisions. An interference between the spin-flip pion exchange and non-flip $a_1$-Reggeon...

The internal structure of jets has been an active research topic in QCD in recent years. In this talk, we propose to use one particular jet substructure - the so-called jet fragmentation function to study spin-dependent distribution and dynamics. In particular, we provide the general theoretical framework for studying the distribution of hadrons inside a jet by taking full advantage of the...

We report a new measurement of transverse single-spin asymmetries for pair-production of jets in collisions of transversely polarized protons at $\sqrt{s}$ = 200 GeV with data taken in 2012 and 2015 at STAR. In this measurement we probe, at high $Q^2$, correlations between the transverse spin ($\vec S$) of a proton, moving in the longitudinal ($\vec p$) direction, and the transverse momenta of...

There have been numerous attempts, both experimentally and theoretically, to understand the origin of the unexpectedly large transverse single-spin asymmetries ($A_N$) for inclusive hadron production at forward rapidity in p$^\uparrow$+p collisions that persist from low to high center-of-mass energies. Two proposed potential sources are the twist-3 contributions in the collinear factorization...

Understanding the transverse spin and momentum structure of the proton is of large interest to the nuclear physics community and it is one of the main goals of the spin physics program at the Relativistic Heavy Ion Collider (RHIC). Transverse single spin asymmetry measurements for particles produced in proton-proton collisions provide insight into initial and final state spin-momentum and...

Recently published measurements from the PHENIX experiment at the Relativistic Heavy Ion Collider will be presented for the transverse single-spin asymmetries (TSSAs) of direct photons, neutral pions, and eta mesons produced at midrapidity in 200 GeV proton-proton collisions. As hadrons, neutral pions and eta mesons are sensitive to nonperturbative spin-momentum correlations both within the...

The STAR experiment at RHIC has measured transverse single-spin asymmetries of W±-bosons in proton-proton collisions at a center-of-mass energy √s = 510 GeV (2017 data). These asymmetries probe correlations between parton motion and the proton spin in the initial state which are described in terms of transverse momentum dependent parton distribution functions (TMD), in this case the Sivers...

In this talk, we report on the first simultaneous extraction of the worm-gear function $g_{1T}$, one of the eight leading-twist TMDs. The study analyzes HERMES, COMPASS and JLab semi-inclusive deep-inelastic scattering data using Monte Carlo techniques. We provide a comparison of $g_{1T}$ obtained from this experimental data with lattice QCD calculations, a large $N_{c}$ analysis, and the...

We perform the first simultaneous global QCD extraction of the transverse momentum dependent (TMD) parton distribution functions and the TMD fragmentation functions in nuclei. We have considered the world set of data from semi-inclusive electron-nucleus deep inelastic scattering and Drell-Yan di-lepton production. In total, this data set consists of 126 data points from HERMES, Fermilab, RHIC...

Transverse Momentum Dependent Parton Distribution Functions (TMD PDFs) can be extracted from the processes that are corresponding to multiple kinematic scales such as Drell-Yan (DY), Semi Inclusive Deep Inelastic Scattering (SIDIS) and e+ e− annihilation. Among the eight leading- twist TMD PDFs, there are two time-reversal odd TMDs, namely Sivers function & Boer-Mulders function, which...

E1039/SpinQuest is a polarized fixed-target Drell-Yan experiment using the 120 GeV proton beam from the Main Injector at Fermilab. The primary goal of SpinQuest is to measure the Sivers asymmetries, aiming to shed light on the fundamental question, “Do the light sea quarks contribute to the intrinsic spin of the nucleon via their orbital angular momentum?”. The Sivers asymmetry was first...

The COMPASS experiment at CERN performed in 2015 and 2018 Drell-Yan measurements using a 190 GeV negative pion beam scattering off a NH3 target and nuclear aluminium and tungsten targets. We will present the differential cross section obtained from that measurement in the kinematic in x-Feynman, transverse momentum, and mass. The results will be valuable input for constraining parton...