arXiv subjects

Chentao Tan

Publications and source records attributed to Chentao Tan.

10 recordsLinked to original sources

arXiv2026

Twist-3 gluon GPDs for the nucleon in a spectator model

We investigate the complete set of twist-3 gluon generalized parton distributions (GPDs) of the nucleon at nonzero skewness within a spectator model, in which the nucleon is treated as a two-body system consisting of an active spin-1 gluon and a spin-1/2 spectator particle. The spectator mass is allowed to vary continuously and is described by a spectral function, while the nucleon-gluon-spectator coupling is modeled by an effective vertex containing two form factors. We calculate the twist-3 gluon GPDs over a broad kinematic range and investigate the corresponding impact-parameter-dependent parton distributions, defined as two-dimensional Fourier transforms of the GPDs at zero skewness. In the forward limit, we further obtain the corresponding twist-3 parton distribution functions (PDFs). Our results provide model predictions for twist-3 gluon GPDs and PDFs that can be useful for future phenomenological studies and for investigating observables at current and future collider facilities.

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arXiv2026

Accessing gluon GTMD $F^g_{1,4}$ via the $\langle\sin(2ϕ)\rangle$ azimuthal asymmetry of exclusive $π^0$ production in $ep$ collisions

The longitudinal single-target spin asymmetry in exclusive $π^0$ production in $ep$ collisions is a sensitive probe of the imaginary part of the gluon generalized transverse momentum dependent distribution $F_{1,4}^g$. It appears as a characteristic $\sin(2ϕ)$ azimuthal correlation between the transverse momenta of the scattered electron and the recoil proton, generated by Coulomb-nuclear interference; consequently, the Primakoff process should be included. We compute the relevant gluon distributions in a light-front spectator model of the proton that explicitly incorporates gluonic degrees of freedom. This work presents the first model calculation of the imaginary part of $F_{1,4}^g$ and delivers predictions for the resulting asymmetries in kinematics relevant to the planned Electron-Ion Colliders (EIC and EicC), providing theoretical predictions for upcoming measurements.

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arXiv2026

Near-threshold photon-proton production of $J/ψ$ and $Υ$

We study the near-threshold exclusive photoproduction of heavy vector mesons (quarkonia $J/ψ$ and $Υ$) off the proton within the framework of generalized parton distribution (GPD) factorization. The gluon GPDs are computed using a spectator model in which the proton emits a gluon and the remaining constituents are treated as a single spectator particle. Model parameters are determined by fitting the gluon unpolarized and helicity collinear parton distribution functions (PDFs) from global analyses. We compare our results with the latest near-threshold $J/ψ$ production data from the GlueX and $J/ψ$-007 experiments at Jefferson Laboratory, finding good agreement for both differential and total cross sections. Predictions are also provided for $Υ$ photoproduction, which can be tested at future Electron-Ion Colliders.

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arXiv2025

The $\sin(2ϕ)$ azimuthal asymmetry in exclusive $π^0$ production

The $\sin(2ϕ)$ azimuthal angular correlation between the transverse momenta of the scattered electron and the recoil proton in the $ep\to e^\prime p^\prime π^0$ process provides a probe for quark orbital angular momentum. We numerically calculate this asymmetry for the future Electron-Ion Collider (EIC) in the U.S. and China (EicC) kinematics using a light-front quark-scalar-diquark model, in which the light-front wave functions (LFWFs) are derived from the soft-wall AdS/QCD framework. We also investigate the properties of the valence quark angular momentum expressed in terms of helicity-independent and helicity-dependent parton distributions. This study aims to establish theoretical constraints on the asymmetry sensitive to the quark orbital angular momentum prior to its first experimental measurement.

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arXiv2024

Chiral-even twist-3 GPDs for the proton in a spectator diquark model

We investigate the chiral-even twist-3 generalized parton distributions (GPDs) of valence quarks in the proton at nonzero skewness $ξ$, using a spectator model with scalar and axial-vector diquarks. We consider the exponential form factor for the nucleon-quark-diquark vertex and the axial-vector diquark with light-cone transverse polarization. We analyze the dependence of GPDs on the longitudinal momentum fraction $x$ at different $ξ$, and on the square of the transverse momentum transfer $Δ^2_T$ at different $x$. Our numerical results reveal distinct discontinuities in all twist-3 GPDs except $G_1$ and $\tilde{G}_1$. By taking the forward limit, we obtain the twist-3 parton distribution function $g_T$, which encodes the transverse spin distribution of quarks. We also compare the kinetic orbital angular momentum and the spin-orbit correlations of quarks defined by the twist-2 and twist-3 GPDs, respectively.

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arXiv2024

Gluon GTMDs at nonzero skewness and impact parameter dependent parton distributions

We investigate the leading twist generalized transverse momentum dependent parton distributions (GTMDs) of the unpolarized and longitudinally polarized gluons in the nucleon. We adopt a light-front gluon-triquark model for the nucleon motivated by soft-wall AdS/QCD. The gluon GTMDs are defined through the off-forward gluon-gluon generalized correlator and are expressed as the overlap of light-cone wave functions. The GTMDs can be employed to provide the generalized parton distributions (GPDs) by integrating out the transverse momentum. The Fourier transform of the GPDs encodes the parton distributions in the transverse position space, namely, the impact parameter dependent parton distributions (IPDs). We also calculate the three gluon IPDs corresponding to the GPDs $H^g$, $E^g$ and $\widetilde{H}^g$, and present their dependence on $x$ and $b_\perp$, respectively.

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arXiv2023

Gluon Wigner distributions in a light-cone spectator model

We study the gluon Wigner distributions of the proton which are the phase-space distributions containing the most general one-parton information. Using the proton wave functions deduced from a light-cone spectator model that contains the gluonic degree of freedom, we calculate the Wigner distributions of the unpolarized and longitudinally polarized gluon inside the unpolarized/longitudinally polarized proton via the Fock-state overlap representation, respectively. We present the numerical results of the transverse Wigner distributions in which the longitudinal momentum fraction is integrated out. The mixed Wigner distributions as functions of $b_y$ and $k_x$ are also presented. We also provide the canonical gluon orbital angular momentum and spin-orbit correlations deduced from the gluon Wigner distribution.

hep-ph↗

arXiv2023

Gluon generalized parton distributions and angular momentum in a light-cone spectator model

We study the leading twist gluon generalized parton distributions (GPDs) and the gluon angular momentum inside the proton within a light-cone spectator model. Using the light-cone wave functions derived from the model, we provide the expressions of these distributions at the particular kinematical point $ξ=0$ in the overlap representation. The numerical results of the $H^g$, $E^g$, $\tilde{H}^g$, $H_T^g$ and $E_T^g$ as functions of $x$ at different $Δ_T$ are presented. Particularly, $H^g$, $\tilde{H}^g$ at non-zero $Δ_T$ are different from their forward counterparts, the unpolarized distribution $f_1^g$ and the helicity distribution $g_1^g$, respectively. We also obtain the total angular momentum of the gluon contributed to the proton spin $J^g=0.19$, which is consistent with the recent lattice calculation after the uncertainties is considered. The kinetic orbital angular momentum is also calculated and is negative in our model.

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arXiv2022

The quark quasi Sivers function and quasi Boer-Mulders function in a spectator diquark model

We compute the leading-twist T-odd quasi-distributions of the proton in a spectator model with scalar and axial-vector diquarks: the quasi Sivers function $\tilde{f}_{1T}^\perp(x, k_T^2; P_z)$ and the quasi Boer-Mulders function $\tilde{h}_1^\perp(x, k_T^2; P_z)$. We obtain the quark-quark correlators in the four-dimensional Euclidian space by replacing $γ^+$ and $σ^{i+}$ in the light-cone frame with $γ_z$ and $σ_{iz}$. We show by analytical calculation that the results of $\tilde{f}_{1T}^\perp$ and $\tilde{h}_1^\perp$ derived from the correlators can reduce to the expressions of the corresponding standard T-odd distributions $f_{1T}^\perp(x, k_T^2)$ and $h_1^\perp(x, k_T^2)$ in the limit $P_z\rightarrow\infty$. The numerical results for these quasi-distributions and their first transverse moments for the $u$ and $d$ quarks in different $x$ and $P_z$ regions are also presented. We find that $\tilde{f}_{1T}^{\perp(1)}(x, P_z)$ and $\tilde{h}_1^{\perp(1)}(x, P_z)$ in the spectator model are fair approximations to the standard ones (within 20-30\%) in the region $0.1 2.5$ GeV as fair approximation.

hep-ph↗

arXiv2022

Quark spin-orbit correlations in the pion meson in light-cone quark model

We study the correlation between the quark spin and orbital angular momentum inside the pion meson. Similar to the case inside the nucleon, the longitudinal spin-orbit correlation $C_z^{q/π}$ in pion meson can be expressed in terms of the corresponding generalized parton distributions (GPDs) and generalized transverse momentum distributions (GTMDs). This provides new information about the spin structure of the pion. Using the wavefunctions of the pion in the light-cone quark model and the overlap representation for GPDs and GTMDs, we present the analytical results for the quark longitudinal spin-orbit correlation. We find that the GPD approach and the GTMD approach lead to the same results. The numerical results is also obtained, showing that the correlation in pion is anti-aligned. In addition, we compare $C_z^{q/π}$ from the GPD approach and the GTMD approach, with $x$ and the transverse momentum $k_T$ unintegrated.

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