High-energy collision processes where multiple hadrons are detected in the final state provide a rich structure to probe QCD dynamics. Establishing the correct quantum field-theoretic operator definition of multi-hadron fragmentation functions is critical in this regard. I will discuss the latest developments in the theory of multi-hadron fragmentation functions in interpreting them as number...
Generalized parton distributions (GPDs) are accessible through experimental processes such as deep virtual Compton scattering (DVCS) and deep virtual meson production (DVMP). Extracting GPDs directly from Compton form factors is complicated by the inherent ambiguity of deconvolution when parametrizing GPDs directly in momentum fraction $x$-space using double distributions. To overcome this...
We discuss all-order factorization for the virtual Compton process at next-to-leading power (NLP) in the $\Lambda_{\rm QCD}/Q$ and $\sqrt{-t}/Q$ expansion (twist-3), both in the double-deeply-virtual case and the single-deeply-virtual case. We use the soft-collinear effective theory (SCET) as the main theoretical tool. We conclude that collinear factorization holds in the double-deeply virtual...
We extend the formalism of Phys.Rev.Lett. 133 (2024) 24, 241901 to helicity generalized parton distributions (GPDs) with the skewness dependence modeled by t-channel exchanges of spin-j operators in AdS space. Based on the conformal moment expansion, the GPDs are obtained through Mellin-Barnes integrals which bypass the convolution problem and are valid for all values of the skewness...
I will present recent progress on the extraction of GPDs from data utilizing machine learning.
Zero mode issue in the minus-minus component calculation of the transition form factors in the light-front dynamics Among the three forms of Hamiltonian dynamics Dirac proposed in 1949, the light-front dynamics (LFD) has the most kinematical Poincare operators. In particular, the longitudinal boost operator becomes kinematical in the LFD. The LFD has very distinct vacuum properties, leading to...
Inverse problems are ubiquitous in hadron structure and tomography, where accurately characterizing uncertainties is crucial for unraveling new physics hiding within these uncertainties. In this new precision era of QCD, it is vital to create a translation between our physics and next generation AI/ML algorithms, using tools such as evidential deep learning and information-theoretic metrics to...
I'll discuss calculation of the NLO corrections to the unpolarized quark TMDPDFs using the factorization scheme defined in arXiv:2311.16402. The scheme aims to take into account the all collinear twist content of the TMDPDFs in the region of large $b_\perp\lesssim\Lambda^{-1}_{QCD}$ and bridge together the limits of large and small-x. I'll discuss different aspects of this derivation including...
The spacetime structure underlying hadronic processes plays a
central role in shaping their factorization properties. In many
important cases, the relevant dynamics unfold along two opposing
light-cone directions, and any deviation from the lightcone is commonly
assumed to be negligible at leading power. In this presentation, I will
demonstrate the significance of these off lightcone...
We present the first extraction of transverse-momentum-dependent distributions of unpolarized quarks from experimental Drell-Yan data using neural networks to parametrize their nonperturbative part. We show that neural networks outperform traditional parametrizations providing a more accurate description of data. This work establishes the feasibility of using neural networks to explore the...
In this talk, I will discuss recent advances in our ability to image parton distribution functions (PDFs) in bound nucleons. I will review topics from last year’s QCD Evolution workshop, such as methods for extracting nuclear-modified PDFs and TMDs. Additionally, I will discuss perturbative approaches that show how the evolution of TMD PDFs in Drell-Yan (p+A) collisions follows a BFKL...
The understanding of the three-dimensional internal structure of the proton has significantly been developed over the past few decades. In particular, the extraction of Transverse Momentum Dependent distributions (TMDs) from global fits of experimental data has now reached an impressive level of precision. In this talk, I will present first indications of flavor dependence emerging from the...
In this work we explore the possibilities to obtain the values of the CollinsSoper kernel and the strong coupling constant offered by what so far is the highest order result ever achieved in perturbation theory, that is for the energy correlators in the back-to-back limit at $N^4LL+N^3LO$.
The cross-section was implemented within ARTEMIDE’s code, using the $\zeta$-prescription for the...
In this talk I present a new determination of the unpolarised fragmentation functions (FFs) for Lambda production from single-inclusive e+e- annihilation, semi-inclusive deep-inelastic scattering and pp collisions data. The analysis is done at both next-to-leading order (NLO) and next-to-next-to-leading order (NNLO). We extract the unpolarised FFs defining a parametrisation in terms of a...
Study of the origin of transverse single-spin asymmetries has triggered the development of the twist-3 formalism and the transverse-momentum-dependent parton distribution functions (TMDs). Measurement of the azimuthal distribution of identified hadrons within a jet in transversely polarized hadronic interactions provides an opportunity to study the TMD physics in the final state, {\it i.e.},...
I would like to present recent work done for developing an event generator aimed at making projections for hard exclusive reactions such as Compton-like reactions and meson production, for JLab to EIC energies. We extended our framework to include new reactions (phi, gamma-meson...), radiative corrections, etc. In this talk we also would like to discuss the connections between this work and...
I will discuss some recent progresses in constraining the gravitational form factors (GFFs) of the proton via near-threshold heavy quarkonium production with next-to-leading order alpha_S corrections. Particularly, I will show with Bayesian inference that such processes provide important constraint on the gluonic GFFs as well as the quark GFFs whose contributions emerge at next-to-leading order.
In the Standard Model of particle physics, the axial current is not conserved, due both to fermion masses and to the axial anomaly. Using perturbative quantum chromodynamics, we calculate matrix elements of the local and non-local axial current for a gluon target, clarifying their connection with the axial anomaly. In so doing, we also reconsider classic results obtained in the context of the...
Generalized parton distributions (GPDs) are functions of four variables, one of which is a renormalization scale. The functional dependence on this renormalization scale is fully determined by a renormalization group equation---or "evolution equation"---that can be derived from perturbative QCD. A fast numerical implementation of the scale evolution is vital to any global phenomenology effort....
Within the pseudo-PDF framework, we investigate the perturbative contributions to correlators that are used to study transverse momentum dependent parton distributions (TMDs) on the lattice. Our results contain the full perturbative corrections which arise as artifacts from performing the calculation for a Euclidean separation between the parton fields, as well as the corrections which yield...
A new global QCD analysis by the JAM collaboration performs the first extraction of transversity PDFs and tensor charges using both the Transverse Momentum Distribution (TMD) and Dihadron Fragmentation Function (DiFF) channels simultaneously, including all currently available experimental data. Known theoretical constraints on transversity, namely, its small-$x$ asymptotic behavior and the...
I will present on the extraction of disconnected contribution to the isoscalar matrix elements for light and strange quarks for the proton using Lattice QCD. While the connected contributions dominate the disconnected contributions are non-zero and must be considered to properly determine the matrix elements. In the case of the strange quark, there is no connected contribution, thus it is...
We apply the valence quark model to constrain the non-perturbative initial condition for the small-x helicity evolution. The remaining free parameters are constrained by performing a global analysis to the available polarized small-x deep inelastic scattering data. A good description of the world data is obtained with only 8 free parameters. The model parameters are tightly constrained by the...
We calculate $(\sqrt{-t}/Q)^k $ and $(m/Q)^k$ power corrections with $k\le 4$, where $m$ is the target mass and $t$ is the momentum transfer, to several key observables in Deeply Virtual Compton Scattering (DVCS). We find that the power expansion is well convergent up to $|t|/Q^2\lesssim 1/4$ for most of the observables, but is naturally organized in terms of $1/(Q^2+t)$ rather than the...
When electrons strike a proton or nuclear target, there is a regime where electroproduction of the highest momentum pion or rho mesons proceeds by a perturbatively calculable process. The process is not the leading twist fragmentation process but rather a higher twist process that produces kinematically isolated mesons. Our calculations demonstrate, that in conditions that can be expected at...
