Conveners
WG5: Spin and 3D Structure: Session 1
- yoshitaka hatta (BNL)
- Yoshiyuki Miyachi (Yamagata University (JP))
- Qinghua Xu (Shandong University)
WG5: Spin and 3D Structure: Session 2
- Yoshiyuki Miyachi (Yamagata University (JP))
- Qinghua Xu (Shandong University)
- yoshitaka hatta (BNL)
WG5: Spin and 3D Structure: Session 3
- Yoshiyuki Miyachi (Yamagata University (JP))
- Qinghua Xu (Shandong University)
- yoshitaka hatta (BNL)
In semi-inclusive deep inelastic scattering (SIDIS) the non-zero transverse momentum of partons is reflected in the transverse momentum $P_T$ of the produced hadrons and in their azimuthal distribution. Assuming Gaussian dependence of transverse momentum dependent (TMD) PDFs and fragmentation functions (FFs) upon quark transverse momentum, exponential distribution of $P_T^2$ is expected. For...
In this talk we present the most recent extraction of unpolarized transverse-momentum-dependent (TMD) parton distribution functions (PDFs) and TMD fragmentation functions (FFs) from global data sets of Semi-Inclusive Deep-Inelastic Scattering (SIDIS), Drell-Yan and Z boson production. The fit is performed at the (next-to)$^3$ leading logarithmic accuracy in the resummation of qT-logarithms and...
Large energy Drell-Yan and $Z$-boson production data have been used to extract transverse momentum dependent parton distribution functions (TMDPDFs). Evolution of TMDPDFs is conveniently described in $b_T$ space, the Fourier conjugate to transverse momentum. The cross section depends on perturbative QCD calculations and non-perturbative TMD functions at low and high regions of the $b_T$...
Extending TMD factorization to thrust-dependent observables entails difficulties ultimately associated with the behavior of soft radiation. As a consequence, the definition of the TMDs has to be revised, while keeping (and extending) its universality properties. Moreover, the regularization of the rapidity divergences intertwines with the thrust dependence, leading to a new kind of...
The lepton-jet momentum imbalance in deep inelastic scattering events offers a useful set of observables for unifying collinear and transverse-momentum-dependent frameworks for describing high energy Quantum Chromodynamics interactions. A recent first measurement was made [1] of this imbalance in the laboratory frame using positron-proton collision data recordedf with the H1 experiment at HERA...
COMPASS is a fixed target high energy physics experiment located at the M2 beamline (SPS, North Area) at CERN. The experiment is collecting data since 2002 covering a broad range of physics topics. Experimental results obtained by COMPASS for spin (in)dependent azimuthal azimuthal effects in semi-inclusive deep inelastic scattering (SIDIS) measurements, play an important role in the general...
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),...
In [1] it was shown that gT(x) can contribute to a Single Spin Asymmetry in SIDIS. This contribution
arises through certain two-loop diagrams which provide the necessary imaginary phase for the asymmetry. In this
talk, I discuss our work in [2] where we presented numerical estimates of the above asymmetry at the planned Electron-Ion
Collider. Therein we also included an analogous...
Understanding the transverse spin and momentum structure of the proton is of great 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...
The transversity distribution, $h^q_1(x)$, describes transversely polarized quarks inside a transversely polarized nucleon. As $h^q_1(x)$ is chiral-odd, it can only be accessed via a process where it couples to another chiral-odd function, such as the spin-dependent interference fragmentation function (IFF), in $p^\uparrow p$ collisions. The coupling of $h^q_1(x)$ and IFF yields an...
While it has been known since the 60s that nucleons are composed of quarks and gluons, very little is understood about the mechanisms responsible for the emergence of nucleons from these partons. Generalized Parton Distributions (GPDs) provide the opportunity to obtain a 3-dimensional, tomographic picture of a nucleon. Moreover, GPDs are related to total angular momentum, mass and pressure...
Generalized Parton Distributions are studied in exclusive reactions
like Deeply Virtual Compton Scattering (DVCS). In 2016 and 2017
DVCS was measured at COMPASS using 160 GeV positively and negatively
charged polarized muon beams provided by the M2 beamline of the SPS at CERN and
which was scattered off a 2.5 m long liquid hydrogen target. To perform an
exclusive measurement the...
Motivated by the research program of the Electron Ion Collider,
we have calculated the two-loop (NNLO) flavor-singlet (vector) coefficient
function of deeply virtual compton scattering (DVCS).
Apart from the result and some technical aspects of the calculation,
I will present numerical estimates of the size of the NNLO
correction to the corresponding Compton form factors.
Authors: Oskar Grocholski, Bernard Pire, Pawel Sznajder, Lech Szymanowski, Jakub Wagner
Extraction of generalized parton distributions (GPDs) from experimental data requires us to consider various exclusive processes on hadrons. The most popular ones - such as DVCS, TCS, DVMP - have been already well studied at higher QCD order. In our recent works, we developed the NLO description (in...
We discuss the use of machine learning techniques in effectively nonparametric modelling of generalised parton distributions (GPDs) in view of their future extraction from experimental data. Current parameterisations of GPDs suffer from model dependency that lessens their impact on phenomenology and brings unknown systematics to the estimation of quantities like Mellin moments. The new...
In QCD, the proton mass can be decomposed into contributions from quarks and gluons. But somewhat similar to the case of the proton spin, this decomposition is not unique. In this talk, we give an up-to-date review and comparison of different sum rules for the proton mass. We also discuss how future measurements at the EIC could further this field.
A quantitative understanding of how gluonic spin contributes to the spin of the proton has been a central goal of the RHIC spin program. In polarized pp collisions, the large kinematic coverage of the Solenoidal Tracker At RHIC (STAR) provides sensitivity to gluons over a broad range in their momentum fraction x through the qg and gg scattering processes that dominate jet production at...
We perform the first simultaneous global QCD analysis of spin-averaged and spin-dependent parton distribution functions (PDFs), including single jet production data from unpolarized and polarized hadron collisions. We critically assess the impact of SU(3) flavor symmetry and PDF positivity assumptions on the quark and gluon helicity PDFs, and find strong bias from these, particularly on the...
We use small-$x$ helicity evolution equations to analyze the world polarized DIS and Semi-inclusive DIS (SIDIS) data. After successfully describing the $g_1$ structure function extracted from polarized DIS, we extend this analysis to the small-$x$ $g^h_1$ structure function measured in polarized SIDIS. The fit is performed through a Monte-Carlo analysis within the JAM global framework....
The virtual photon asymmetry $A_1$ is one of the fundamental quantities that provide information on the spin structure of the nucleon. The value of $A_1$ at high $x_{Bj}$ is of particular interest because valence quarks dominate in this region, which makes it a relatively clean region to study the nucleon structure. Several theoretical calculations, including naive SU(6) quark model,...
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 COMPASS experiment (M2 beamline, SPS, CERN).
In 2015 and 2018 COMPASS performed Drell-Yan measurements using a 190 GeV $\pi^-$ beam interacting with a transversely polarized $NH_3$ and unpolarized...
Angular correlations present in dijet photoproduction are studied, for the first time, using ultraperipheral lead-lead collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV. The second moment of the angular distribution, $\langle \cos(2\Phi) \rangle$, where $\Phi$ is the angle between the vector sum $\vec{Q}_\mathrm{T}$ and the vector difference $\vec{P}_\mathrm{T}$ of the...
Factorization theorems are known to be extremely powerful tools in high-energy particle physics. Processes like SIDIS, Drell-Yan vector-boson production, Higgs-boson production through gluon fusion and $e^+e^-$ to jets and/or hadrons are just some examples of processes that have been thoroughly investigated by applying rigorous factorization formulae. Furthermore, if in these processes the...
Semi-inclusive DIS is a natural process for the measurement of transverse momentum dependent distributions. While current fits and analysis use cross section at leading power in the ratio of transverse momenta and center of mass energy, we have computed and factorized the cross section at next-to-leading power, opening the way to a finer set of studies. The proof are done using the...
In this talk we present the potential of $\eta_{b,c}$ production from hadronic collisions to access the gluon TMD PDFs. In particular, we explore the phenomenology of the unpolarized and linearly polarized gluon TMD PDF in unpolarized collisions for different kinematic settings, and the potential of a fixed-target experiment at the LHC to access T-odd distributions such as the gluon Sivers TMD PDF.
The longitudinal spin decomposition of the proton provides key information about its structure. While the quark spin contribution was well constrained by the polarized deep inelastic scattering (DIS), the gluon spin contribution remains less known. Direct photon, jet, and charged pion production in the longitudinally polarized proton ($\vec{p}+\vec{p}$) collisions can probe the gluon spin at...
By considering double spin asymmetry (DSA) in exclusive dijet production in $ep$ collisions, we demonstrate for the first time that the $cos(\phi)$ angular correlation between the scattered electron and proton is a direct probe of the gluon orbital angular momentum and its interplay with the gluon helicity. We also make an estimate of the DSA for typical kinematics of the future Electron Ion Collider.
I will discuss the extension of the nucleon spin sum rule to QCD×QED. I will present the QED corrections to the evolution of the quark and gluon helicity and orbital-angular-momentum (OAM) distributions, which are calculated for the first time, and discuss the necessary inclusion of photon and lepton helicity and OAM distributions.
We investigate the relation between the topology of a nucleon and its spin composition. We approach this question in 1+1 dimensional single-flavor QCD with a large number of color. In this limit the theory can be shown to be dual to the exactly solvable sine-Gordon model. The spectrum of baryons and mesons is known analytically, and the baryon is a topological kink of the sine-Gordon model....
Seven years after the preliminary data were made available, the CLAS collaboration published both CLAS and CLAS12 results on the beam-spin asymmetry in semi-inclusive dihadron production off proton target. We present the phenomenological extraction of the associated twist-3 collinear PDF, e(x), made possible through the analysis of dihadron fragmentation function. We will discuss the extent to...
Generalized Parton Distribution (GPDs) are universal functions which provide a comprehensive description of hadron properties in terms of quarks and gluons. Deeply Virtual Compton Scattering (DVCS) is the simplest process involving GPDs. In this talk, we will present the latest $ep \to e p \gamma$ cross sections obtained from Jlab Hall A data at three values of the Bjorken variable $x_B$. In...
The Electron-Ion Collider (EIC), to be built at Brookhaven National Lab within this decade, will provide high-precision access to the gluon and sea-quark dominated region of the nucleon. With luminosities of $10^{33-34}$ cm$^{-2}$s$^{-1}$, centre of mass energies 20-140 GeV, highly polarised electron and proton / light-ion beams and hermetic detectors, the collider will enable measurements of...
The proton structure can be parameterized through Generalized Parton Distributions (GPDs) - a formalism that describes exclusive processes and allows to perform tomography of the nucleon. Measurements of exclusive processes, such as Deeply Virtual Compton Scattering (DVCS), are sensitive to complex integrals of GPDs, known as Compton Form Factors (CFFs). To gain access to the elusive CFF E for...
We show that exclusive massive photon-pair production in pion-nucleon collisions can be systematically studied in terms of QCD factorization approach if the photon's transverse momentum with respect to the colliding pion $q_T\gg\Lambda_{\rm QCD}$. We demonstrate that leading power non-perturbative contributions to the scattering amplitudes of this exclusive process are process-independent and...
Generalized distribution amplitudes (GDAs) are the s-t crossing quantities of generalized parton distributions (GPDs), which can be measured in the process of $\gamma^* + \gamma \rightarrow M_1+ M_2$. In 2016, the Belle Collaboration released the measurements of differential cross section for $\gamma^* + \gamma \rightarrow \pi+ \pi$, from which the pion GDAs were extracted by using the...
I will discuss recent work on the issues that arise when dealing with ultraviolet renormalization of both collinear and TMD Parton densities. In particulars, I will discuss how some commonly assumed properties like positivity can be violated in standard schemes. I will discuss the ways that using TMD parton densities can help even when dealing with collinear pdfs.
We study back-to-back lepton-jet production in lepton-proton collisions. This process defines two azimuthal angles, the transverse momentum imbalance $q_T$ of the lepton and the jet, and the azimuthal angle of the jet transverse momentum itself. In this work, we study the azimuthal anisotropy for the azimuthal angle difference φ between these two angles. In particular, we provide the...
Covariant parton model is a generalization of the Feyman's parton model which does not prefer any special reference system. Within the framework of covariant parton model, we study the properties of the quark and antiquark correlators determined by the equations of motion of the free partons, and derive the polarization vectors for quarks and antiquarks in mixed-spin and pure-spin states. We...
Recently, exclusive processes have gained increasing attention. Part of this interest comes from the open questions of how the spin of the proton is decomposed into the intrinsic spin and the orbital motions of the constituent parts, along with the possibility of obtaining energy-momentum densities through exclusive processes. In this talk, we present the EpIC Monte Carlo event generator for...
The matrix elements of the energy momentum tensor (EMT) between plane wave states define gravitational form factors (GFFs) which provide information about spatial distribution of energy, momentum and angular momentum. The Druck gravitational form factor is related to the mechanical stability of the nucleon and gives information about the spatial distributions of the forces inside the hadron....
Hard exclusive pion production is a well established tool to study Generalized Parton Distributions (GPDs). During the last decade, extensive studies have been performed on hard exclusive $\pi^{0}$ and $\pi^{+}$ production off the proton. However, hard exclusive $\pi^{-}$ production off the proton is so far nearly unexplored. It can be described based on $N\rightarrow\Delta^{++}$ transition...
The structure of the proton has been studied by measuring the parton distribution function, which is the parton density distribution as a function of the longitudinal momentum of the parton, for long time. In the last few decades, the three-dimensional imaging of nucleon, such as the transverse momentum dependent parton distribution functions (TMDs), has received attention to better understand...
There are new polarized structure functions, which do not exist for the spin-1/2 nucleons, in a spin-1 hadron such as the deuteron. In the near future, we expect that physics of spin-1 hadrons will become a popular topic, since there are experimental projects to investigate spin structure of the spin-1 deuteron at the Jefferson Laboratory, the Fermilab, the NICA, the LHCspin, and the...
A sizable cos 4ϕ azimuthal asymmetry in exclusive dipion production near ρ0 resonance peak in ultraperipheral heavy-ion collisions recently has been reported by STAR collaboration. We show that both elliptic gluon Wigner distribution and final-state soft photon radiation can give rise to this azimuthal asymmetry. The fact that the QED effect alone severely underestimates the observed asymmetry...
We re-interpret the jet clustering as an axis-finding procedure which, along with the proton beam, defines the virtual photon transverse momentum $q_T$ in deep inelastic scattering (DIS). In this way, we are able to probe the nucleon intrinsic structures with jets in a fully inclusive manner, similar to the Drell-Yan process. We present the factorization formulae and a complete list of the...
We present a calculation of the $\cos2\phi$ azimuthal asymmetry in $e ~p\rightarrow e ~J/\psi ~Jet~ X$, where $J/\psi-Jet$ pair is almost back-to-back in the transverse plane, within the framework of the generalized parton model (GPM) and assuming TMD factorization. This probes the Weisz{\"a}ker-Williams type linearly polarized gluon distribution. We calculate the asymmetry using...
Understanding the origin of transverse single-spin asymmetries is a long-standing challenge in strong interaction physics. Significant progresses have been made in the last few decades from both the experimental and theoretical sides, which fueled the rapid development of twist-3 and transverse-momentum-dependent (TMD) factorization schemes. Measurement of the azimuthal distribution of...
There have been numerous attempts, both theoretical and experimental, to understand the origin of the unexpectedly large transverse single spin asymmetry ($A_{N}$) for the inclusive hadron production at forward rapidities observed in $p^{\uparrow}$+p collisions at various center-of-mass energies. The twist-3 contributions in the collinear factorization framework and the...
Understanding the origin of the proton spin is one of the most fundamental and challenging questions in QCD. Much progress has been made since the first surprising results %on the spin structure of the proton by the EMC experiment in the late 1980s. However, for the helicity distributions of the proton, contributions from sea quarks, especially from the strange quark (anti-quark),...
Spontaneous polarization of $\Lambda/\bar{\Lambda}$ has been observed over four decades ago, but still eludes a definitive explanation. One possible origin is the effect arising from polarizing fragmentation functions (PFFs), which describe the production of polarized hadrons from the fragmentation of an unpolarized parton. In 2019, the Belle experiment observed significant transverse...
We make a systematic study of $\Lambda$ hyperon polarizations in unpolarized lepton induced semi-inclusive reactions such as $e^-N\to e^-\Lambda X$ and $e^+e^-\to\Lambda h X$. We present the general form of cross sections in terms of structure functions obtained from a general kinematic analysis. This already shows that the produced hyperons can be polarized in three orthogonal directions,...
Forward neutron single spin asymmetries in proton-proton collisions have
been discovered in early polarized RHIC running and have since been used
as local polarimetry by the RHIC experiments. Its creation mechanism can
be explained by the interference of pion and a1 exchange between the
polarized proton and the other hadron. However, the PHENIX experiment
discovered that the asymmetries...
In the high-energy $p + p$ collisions, the transverse single spin asymmetry for very forward neutron production was measured by the PHENIX experiment at three different collision energies, 62, 200, and 500 GeV. It has been explained by an interference between $\pi$ (spin-flip) and $a_1$ (spin non-flip) exchange with a non-zero phase shift. In June 2017, the RHICf experiment has measured the...
We study the unpolarized and the helicity dependent generalized parton distributions (GPDs) for the valence quarks of the proton in both momentum space and position space within the basis light-front quantization (BLFQ) framework. The GPDs for the valence quarks are computed from the eigenvectors of a light-front effective Hamiltonian in the valence Fock sector consisting of a...
We study the non-perturbative leading twist generalized parton quasi distributions (qGPDs) and transversity generalized quasi distributions (qtGPDs) of the pion in the framework chiral quark models. Such quantities can be directly accessed in lattice QCD simulations, hence our model predictions gain practical significance. We also explore the corresponding Ioffe distributions and various form...
We present the first-ever global QCD analysis of the semi-inclusive DIS data using Monte Carlo techniques to extract the worm-gear TMD $g_{1T}$. The relevant data are available from HERMES, COMPASS and JLab. We compare our results for $g_{1T}$ with different theoretical approaches such as the large-$N_c$ approximation, the Wandzura-Wilczek-type approximation, and lattice QCD.
We present a global QCD analysis of polarized parton distribution functions (PDFs) that includes the latest polarized $W$-lepton production data from the STAR collaboration at RHIC. These data allow the first data-driven extraction of a nonzero polarized light quark sea asymmetry within a global QCD analysis with minimal theoretical assumptions. We perform a simultaneous extraction of...
Experiment E12-06-121 at Jefferson Lab aims to do a precision measurement of the neutron spin structure function g2 using inclusive inelastic scattering of electrons over a large kinematic range of xBj and Q2. The third moment of the linear combination of the spin structure functions g1 and g2, d2, is one of the cleanest higher twist observables and contains information on the quark-gluon...
Generalised parton distributions (GPDs) defined in the framework of quantum chromodynamics (QCD) are three-dimensional objects containing a wealth of unique information about the nucleon structure. Current attempts to extract GPDs from experimental data are typically based on a single exclusive process known as deeply virtual Compton scattering (DVCS) and its leading order QCD description....
