Conveners
WG5: Spin and 3D Structure 1
- Shohini Bhattacharya
- Caroline Kathrin Riedl (Univ. Illinois at Urbana Champaign (US))
- James Drachenberg (Lamar University)
- Marie Boer (Virginia Tech)
- Jakub Wagner (Institute for Nuclear Studies)
WG5: Spin and 3D Structure 2
- Kornelija Passek-Kumerički (Ruđer Bošković Institute, Zagreb, Croatia)
- Caroline Kathrin Riedl (Univ. Illinois at Urbana Champaign (US))
- Jakub Wagner (Institute for Nuclear Studies)
- James Drachenberg (Lamar University)
- Martha Constantinou
WG5: Spin and 3D Structure 3
- Jakub Wagner (Institute for Nuclear Studies)
- James Drachenberg (Lamar University)
- Caroline Kathrin Riedl (Univ. Illinois at Urbana Champaign (US))
WG5: Spin and 3D Structure 4
- James Drachenberg (Lamar University)
- Jakub Wagner (Institute for Nuclear Studies)
- Caroline Kathrin Riedl (Univ. Illinois at Urbana Champaign (US))
- Jakub Wagner
WG5: Spin and 3D Structure 5
- James Drachenberg (Lamar University)
- Caroline Kathrin Riedl (Univ. Illinois at Urbana Champaign (US))
- Jakub Wagner (Institute for Nuclear Studies)
Description
Spin and 3D Structure
We will present results on Spin Density Matrix Elements (SDMEs) measured in hard exclusive muoproduction of $\rho ^0$, $\omega $ and $\phi$ mesons on the proton at COMPASS using 160 GeV/$c$ polarised $\mu ^{+}$ and $\mu^{-}$ beams scattering off a liquid hydrogen target. The measurements cover the range 5 GeV/$c^2$ $< W <$ 17 GeV/$c^2$, 1.0 (GeV/$c$)$^2$ $< Q^2 <$ 10.0 (GeV/$c$)$^2$ and 0.01...
We study the small-x evolution equation for the gluon generalized parton distribution (GPD) Eg of the nucleon. It is shown that Eg at vanishing skewness exhibits the Regge behavior identical to the BFKL Pomeron, despite its association with nucleon helicity-flip processes. We also consider the effect of gluon saturation and demonstrate that Eg gets saturated in the same way as its...
In this talk we present our theoretical studies of heavy quarkonia pair electro- and photoproduction in the collinear factorization framework. We focus on $J/\psi\ \eta_c$ pair production, and discuss the relation of different observables to generalized parton distributions (GPDs) of gluons. The unpolarized cross-section is dominated by contributions of transversely polarized $J/\psi$ mesons,...
We present a further step toward a global extraction of gluon generalized parton distributions (GPDs). In our previous work we performed the first global analysis of quark GPDs by including lattice quantum chromodynamics (QCD) calculations, global fitted forward parton distribution functions (PDFs), form factors (FFs), and Deeply Virtual Compton Scattering (DVCS) measurements from JLab and...
We will present COMPASS measurements of Deeply Virtual Compton Scattering and of exclusive pi0 production on the proton using 160 GeV polarized mu+ and mu- beams at the CERN SPS impinging on a 2.5m long liquid hydrogen target. The target was surrounded by a barrel-shaped time-of-flight system to detect the recoiling target protons. The scattered muons and the produced real photons were...
We calculate the one-loop quark box diagrams relevant to polarized and unpolarized Deep Virtual Compton Scattering by introducing an off-forward momentum $l^\mu$ as an infrared regulator. Such a regularization enables us to unravel the poles $1/l^2$ related to the chiral anomaly in the polarized case and the trace anomaly in the unpolarized case. We interpret our results in terms of the...
Traditionally, lattice QCD computations of GPDs have been carried out in a frame, where the transferred momentum is symmetrically distributed between the incoming and outgoing hadrons. However, such frames are inconvenient for lattice QCD calculations since each value of the momentum transfer requires a separate calculation, increasing the computational cost. In a recent work...
We present a lattice QCD determination of the nucleon generalized parton distributions (GPDs) from an analysis of the quasi-GPD matrix element within the leading-twist framework. We preform our study on a Nf=2+1+1 twisted mass fermions ensemble with a clover improvement. The faster and more effective lattice QCD calculations of GPDs using the asymmetric frames was applied so that we can...
Both deeply-virtual and photoproduction of mesons offer promising access
to generalized parton distributions and complementary description of different kinematical regions. The higher-order contributions offer stabilizing effect with respect to the dependence on renormalization scales, while higher-twist effects have been identified as especially important in the case of the production of...
The so-called Generalized Parton Distribution (GPDs) contain information about the parton's transverse position versus their longitudinal momentum, and can be accessed in hard exclusive reactions (where all products are known). Most of the current models rely on Deeply Virtual Compton Scattering (DVCS) measurements in their parametrization. However, extracting GPDs from other channels will...
Generalized Parton Distributions (GPDs) have been one of the most important tools to access the nucleon 3D structure including its mass, angular momentum and mechanical properties. However, the extraction of GPDs has been challenging due to its high-dimension nature. Recent progress in lattice QCD have brought in many insights into the studies of GPDs. In this talk I will introduce the GPDs...
Deeply virtual exclusive reactions encode the dynamics of bound partons in hadrons through 3D quantum mechanical correlation functions - the generalized parton distributions; however, there are many levels of abstraction in the analysis from experimental data to information on hadron structure. There is an immediate need to develop advanced phenomenology and computational tools in preparation...
I will present a framework for the analysis of deeply virtual exclusive scattering experiments to enable the extraction of observables from data with a faithful representation of uncertainty. The extraction is focused on obtaining the different quark flavor and scale dependence of the various observables at NLO in perturbative QCD, while using the azimuthal phase dependence as a discriminant...
Mapping the 3D structure of the proton in terms of its spinning quark and gluon constituents is one of the main goals of current hadronic physics investigations, especially the field of femtography. Generalized parton distributions (GPDs) contribute to solving this problem. Fourier transforms of GPDs give single particle spatial densities of quarks and gluons for particular longitudinal...
Generalized parton distributions (GPDs) are important non-perturbative functions that provide tomographic images of partonic structures of hadrons. We introduce a type of exclusive processes for a better study of GPDs, which we refer to as single diffractive hard exclusive processes (SDHEPs), and give a general proof for their factorization into GPDs. We demonstrate that the SDHEP is not only...
Transverse Single Spin Asymmetries (TSSAs) in transversely polarized proton-proton collisions ($p^{\uparrow}+p$) have been a fruitful source for studying the spin structure of the proton. In the 2015 RHIC data taking periods, collisions of polarized protons with nuclei ($p^{\uparrow}+A$) were studied for the first time. The measurements of TSSAs in $p^{\uparrow}+p$ and $p^{\uparrow}+A$...
There have been numerous attempts in the last couple of decades to understand the origin of the unexpectedly large transverse single spin asymmetry ($A_{N}$) of inclusive hadron production at forward rapidities observed in $p^{\uparrow}$+$p$ collisions at different center-of-mass energies ($\sqrt{s}$). The current theoretical framework to explain such a puzzle includes the twist-3...
In the high-energy $p+p$ collisions, the transverse single spin asymmetry for very forward neutron production has been interpreted by an interference between $\pi$ (spin flip) and $a_1$ (spin non-flip) exchange with a non-zero phase shift. The $\pi$ and $a_1$ exchange model predicted the neutron asymmetry would increase in magnitude with transverse momentum ($p_{\scriptsize{\textrm{T}}}$) in...
Using the light-front wave functions (LFWFs) overlap representation, we built a theoretical model for the pion state, that parametrizes different pion parton distribution functions. The model is constructed with two sets of parameters, that can be fitted separately by performing two independent fits: one for the collinear, and one for the transverse direction.
At present, we have been able to...
It is known that the trace anomaly in the QCD energy-momentum tensor $T^{\mu \nu}$ can be attributed to the anomalies for each of the gauge-invariant quark part and gluon part of $T^{\mu \nu}$, and their explicit three-loop formulas have been derived in the $\overline{\rm MS}$ scheme in the dimensional regularization. The matrix elements of this quark/gluon decomposition of the QCD trace...
As one of the essential building blocks of ordinary matter, understanding the proton and the strong force that binds its constituents are of crucial importance. At low $Q^2$, the perturbative description of QCD fails, and it is necessary to employ effective theories such as Chiral Perturbation Theory. One way of directly testing these effective theories is the measurement of polarizabilities,...
Measurements of the longitudinal double-spin asymmetry, $A_{LL}$, by the STAR experiment have contributed significantly to our understanding of the gluon helicity distribution, $\Delta g(x)$, inside the proton. Results from the 2009 inclusive jet measurement, when included into global analyses, indicated substantial positive polarization for gluons with partonic momentum fraction $x$ greater...
The spin physics program at the PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC) remains an essential tool in illuminating the internal spin structure of the proton. One major emphasis of the program is the measurement of longitudinal double spin asymmetries $(A_{LL})$ in a number of different final states from collisions of longitudinally polarized protons $(\vec{p} +...
One of the primary goals of the RHIC spin program is to determine the polarized gluon distribution
function, $\Delta g$, within the proton. At the leading order, proton-proton collisions involve a mixture of
quark-quark, quark-gluon, and gluon-gluon scatterings. At RHIC kinematics, the quark-gluon
and gluon-gluon contributions dominate, which makes RHIC an ideal tool to study $\Delta g$....
Using the spectral representation of the quark propagator we study the Dirac decomposition of the gauge invariant quark propagator, whose imaginary part describes the hadronization of a quark as this interacts with the vacuum.
In light-like axial gauge, we obtain a new sum rule for the spectral function associated to the gauge fixing vector. We then demonstrate the formal gauge invariance...
In the 1970's, Fermilab discovered that $\Lambda$ hyperons are polarized in collisions of unpolarized protons on beryllium. This discovery initiated a 50 year long series of measurements which aimed at solving this $\Lambda$ hyperon polarization puzzle. Although this puzzle remains to be an open question, the self-polarizing feature of $\Lambda$ hyperon has been providing an important...
Transverse Λ (uds) polarization observed over four decades ago contradicted expectations from early leading-order perturbative QCD calculations. Recent studies have linked the polarization to the process of hadronization, where hyperon polarization from unpolarized proton-proton and proton-nucleus collisions comes from either including higher-order twist-3 collinear multi-parton correlation...
Spin dependent quark and gluon distributions can lead to distinctive features in the angular dependances and asymmetries of pp and ep scattering processes. Of particular interest are heavy quark production processes, wherein spin asymmetries of the heavy quarks, correlated with diquarks, adumbrate the underlying spin dependances. Heavy flavor hyperons with diquark spectators as well as top...
Using the self-analyzing decay of the $\Lambda$, the longitudinal spin transfer $D_{LL'}$ to the hyperon from a polarized electron beam scattering off an unpolarized proton target can be determined. For $\Lambda$s produced in the current fragmentation region, this quantity is proportional to the helicity dependent fragmentation function $G_1^\Lambda$ and can provide insight into the spin...
The axial-vector form factors of the light, singly and doubly charmed baryons are investigated in the framework of $SU(4)$ chiral constituent quark model. The axial-vector form factors having physical significance correspond to the generators of the $SU(4)$ group with flavor singlet $\lambda^0$, flavor isovector $\lambda^3$, flavor hypercharge $\lambda^8$ and flavor charmed $\lambda^{15}$...
In operation since 2002, COMPASS is a fixed-target experiment located along the M2 beamline of the CERN SPS. One of the key measurements of its broad physics programme is the investigation of the transverse-momentum and transverse-spin structure of the nucleon, which has been pursued e.g. via measurements of Semi-Inclusive Deep Inelastic Scattering using a 160 GeV/$c$ muon beam and...
I will summarize recent progress in a reformulation of TMD factorization that guarantees a parsonic structure description of the small transverse momentum region while matching to standard fixed order collinear factorization at large transverse momentum. The focus will be on applications to semi-inclusive DIS.
We study the energy-energy correlator (EEC) for the process of unpolarized hadrons production from transversely polarized partons Semi-Inclusive Deep Inelastic Scattering (SIDIS) for the first time. In the factorization formula we present, this event shape observable is correlated with the Collins function in the back-to-back limit. We show the structure functions of all the possible spin...
In this analysis, we report a comparison of transverse momentum dependent parton distribution functions (TMDPDFs) between pions and protons through a simultaneous extraction of collinear and transverse degrees of freedom in the pion. We extract proton TMDPDFs along with pion TMDPDFs from low transverse-momentum dependent fixed-target Drell-Yan data as well as collinear pion PDFs from Drell-Yan...
The investigation of the hadrons spin-(in)dependent structure is one of the main goals of the COMPASS experiment at the M2 beamline of the CERN SPS. In particular, azimuthal transverse spin asymmetries provide a clean access to the transverse momentum dependent parton distribution functions (TMD PDFs) of the nucleon, still poorly known. In 2015 and 2018 COMPASS performed measurements of the...
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...
One of the most important unresolved puzzles of the proton is the “proton spin puzzle”. Originally, the proton spin was assumed to be produced only by the valence quark spins, with no contribution from sea quarks or from gluons, and no contribution from orbital angular momentum. However, the contribution of the spins of both quarks and antiquarks to the proton spin have been measured over the...
Understanding the spin 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). Measurements from data taken by the PHENIX detector with transverse (p$^{\uparrow}$ + p, p$^{\uparrow}$ + Al, p$^{\uparrow}$ + Au) proton polarization play an important role in this, in...
We propose a new definition of unintegrated di-hadron fragmentation functions (DiFFs) which is compatible with the probability interpretation of collinear DiFFs. We also derive the leading-order evolution equations for those DiFFs. Furthermore, we compare our findings in detail with previous results in the literature. Unintegrated DiFFs are important for obtaining information on the...
We perform the first simultaneous extraction of di-hadron fragmentation functions (DiFFs) and transversity PDFs using data from single-inclusive annihilation (SIA) in electron-positron collisions, semi-inclusive DIS, and proton-proton collisions. In particular, we include new SIA data from Belle that provides, for the first time, experimental constraints on the unpolarized DiFFs, as well as...
The transversity distribution function, $h_1^{q}(x)$, where $x$ is the longitudinal momentum fraction of the proton carried by quark $q$, encodes the proton's transverse spin structure at the leading twist. Extraction of $h_1^{q}(x)$ is difficult because of its chiral-odd nature. However, it can be coupled with a spin-dependent interference fragmentation function (FF), $H_1^{\sphericalangle,...
Quarks that are transversely polarized inside a transversely polarized nucleon are described by the transversity distribution, $h^q_{1}(x)$. Since $h^q_{1}(x)$ is a chiral-odd function, the only way to access it is through 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...
The Belle experiment at the asymmetric e+e- collider KEKB provides a large data set not only for the exploration of flavor physics but also for precision QCD studies. The clean initial state is particularly well suited to investigate the process of high-energetic partons fragmenting into final state hadrons. This talk will report the results of recent measurements sensitive to fragmentation...
The Large Hadron Collider beauty (LHCb) experiment provides an opportu-
nity to study hadronization processes, how particular hadrons are formed from scattered quarks and gluons (partons), in the forward region, 2 < η < 5. Going beyond traditional collinear non-perturbative fragmentation functions (FFs), transverse-momentum-dependent (TMD) FFs provide multidimensional information on the...
We present the latest results of the MAP collaboration about the extraction of Transverse-Momentum-Dependent (TMD) distributions at the N$^3$LL logarithmic accuracy in the resummation of q$_T$-logarithms. Firstly, we present the most recent extraction of unpolarized quark TMD parton distribution functions (TMD PDFs) in the proton and fragmentation functions (TMD FFs) from a global fit of...
Artificial Neural Networks (ANNs) are quickly becoming an invaluable tool for information extraction and modeling. An unbiased ANN model can be built to make predictions of the Transverse Momentum-dependent Distributions (TMDs) based on global fit to Semi Inclusive Deep Inelastic Scattering (SIDIS) and Drell-Yan (DY) data. A preliminary analysis will be presented on the extraction of the...
The transverse-momentum-dependent parton distributions (TMDs) provide a 3D imaging of the proton and other hadrons in high-energy scattering experiments, such as those at Fermilab, Jefferson Lab, RHIC and LHC. Recent years have seen significant progress in the global fitting of TMDs from experiments, and along with that is a lattice QCD program aiming at first-principles calculation of these...
In this talk, I will present our recent work on transverse momentum dependent factorization and resummation at sub-leading power in Drell-Yan and semi-inclusive deep inelastic scattering. In these processes the sub-leading power contributions to the cross section enter as a kinematic power correction in the leptonic tensor, and the kinematic, intrinsic, and dynamic sub-leading contributions to...
In the light-front quark-diquark model (LFQDM), the higher twist generalized transverse momentum dependent distribution (GTMD) $F_{31}(x, {\bf p_\perp^2},{\bf \Delta_\perp^2})$ for the proton has been analyzed. We have derived the GTMD overlap equation by the analysis of GTMD correlator, employing the light-front wave functions in both the scalar and vector diquark situations. With the...
