arXiv subjects

Chengdong Han

Publications and source records attributed to Chengdong Han.

At least 19 recordsLinked to original sources

arXiv2026

Pion and Kaon PDFs via Infrared-Safe Evolution augmented by $J/\psi$ Data Constraints

Probing the partonic structure of the pion and the kaon provides essential insights into the non-perturbative dynamics of QCD, yet their parton distribution functions (PDFs) remain poorly constrained due to the scarcity of high-precision experimental data, especially for the gluon distributions. We present an improved determination of pion and kaon PDFs within the dynamical parton model combined with the maximum entropy method (MEM) framework. Our analysis features two key advancements: firstly, we employ an infrared-safe QCD evolution scheme, allowing the evolution to be reliably extended down to very low $Q^2$, approaching the hadronic scale; secondly, we incorporate pion- and kaon-induced $J/\psi$ hadroproduction data as crucial constraints in the global fit. We find that our approach yields a good description of the available Drell-Yan data, deep-inelastic scattering structure functions ($F_2$), and $J/\psi$ production across various energies and targets. The results provide significantly improved constraints on the gluon distributions at moderate and large $x$ in both the pion and the kaon, offering a more complete picture of their internal structure.

hep-ph↗

arXiv2026

A practical methodology for $\Lambda$ global polarization extraction in fixed-target experiments

Non-central heavy-ion collisions generate large orbital angular momentum in the created medium, which leads to polarization of final-state particles via spin-orbit coupling, known as global spin polarization. The observation of significant global polarization of $\Lambda$ hyperon in heavy-ion collisions indicates that the quark-gluon plasma is the most vortical fluid known in nature. Exploring $\Lambda$ global polarization at lower energies is important for understanding spin dynamics across different regions of the quantum chromodynamics (QCD) phase diagram. Low-energy nuclear experiments are typically conducted with asymmetric detector acceptance, as in fixed-target collisions at RHIC-STAR, and at facilities such as FAIR, NICA, HIAF and HIRFL-CSR. The asymmetric rapidity coverage in these experiments enhances the coupling between directed flow and detector inefficiencies, creating significant bias in $\Lambda$ global polarization measurements. In this paper, we propose a methodology to eliminate such bias arising from asymmetric detector acceptance. The method is validated using realistic detector simulations based on the STAR fixed-target configuration.

physics.data-an↗

arXiv2025

First Extraction of the $\phi$-$^{4}\mathrm{He}$ scattering length from near-threshold $\phi$ photoproduction on helium-4

We present a model-independent extraction of the phi-4He scattering length from near-threshold phi photoproduction on helium-4, based on LEPS Collaboration data for the coherent process gamma + 4He -> phi + 4He and the Vector Meson Dominance framework. Assuming an energy-independent differential cross section, we extract the absolute value of the phi-4He scattering length |alpha_{phi4He}| = (3.33 +- 0.06) x 10^{-4} fm from a fit at threshold t_thr. This value is orders of magnitude smaller than those for phi-N and phi-d scattering lengths, indicating an inverse dependence of |alpha_VA| on the target nucleus mass. Our results provide new insight into the phi-nucleus interaction, supporting the notion of weak phi-nucleus coupling. We further explore the dependence of |alpha_VA| on the vector meson mass, the target atom mass, and the threshold energy. An approximate exponential suppression of |alpha_VA| is observed with increasing vector meson mass or target atom mass, indicating that heavier vector mesons or heavier target nuclei exhibit weaker couplings in vector meson-nucleus interactions.

hep-ph↗

arXiv2025

Revisiting the deuteron mass radius via near-threshold $\rho^0$, $\omega$ and $\phi$ meson photoproduction

We present a comprehensive analysis of near-threshold photoproduction of $\rho^0$, $\omega$, and $\phi$ mesons on a deuterium target, utilizing published datasets from DESY and SLAC for $\rho^0$ and $\omega$ production, as well as data from the LEPS and CLAS Collaborations for $\phi$ production. In extracting the deuteron mass radius, we adopt a dipole parametrization for the scalar gravitational form factor, which effectively captures the $|t|$-dependence of the differential cross sections associated with vector meson photoproduction. In addition, results from alternative commonly used form factor parametrizations are also considered and compared. Employing the vector meson dominance (VMD) framework and invoking low-energy Quantum Chromodynamics (QCD) theorems, we extract the deuteron mass radius from near-threshold photoproduction data of $\rho^0$, $\omega$, and $\phi$ mesons. The mass radii obtained from the various datasets are found to be consistent within statistical uncertainties, yielding an average value of $2.03 \pm 0.13$ fm under the dipole form assumption. We also provide a detailed discussion of the sensitivity of the extracted radius to different choices of gravitational form factor models. Our result represents a significant improvement in precision compared to earlier estimates based solely on $\phi$ meson photoproduction, offering new constraints for theoretical models of nuclear structure and deepening our understanding of the mass distribution within the deuteron.

hep-ph↗

arXiv2024

Unifying the landscape of nucleon structure: an infrared-safe evolution scheme

A novel approach for describing the evolution of nucleon structure from the low-$Q^2$ regime to the high-$Q^2$ asymptotic region is proposed. This infrared-safe scheme modifies the parton distribution evolution equations to incorporate the corrections from emergent hadron mass mechanisms and parton-parton recombination at low $Q^2$. The effective parton mass, generated by dynamical chiral symmetry breaking, slows the evolution of parton distributions in the infrared region, causing the DGLAP evolution to freeze when $Q^2\ll M_{\rm q/g}$. Notably, this scheme renders the high-$Q^2$ parton distributions insensitive to the choice of input hadronic scale. The parton-parton recombination effect is crucial in suppressing the rapid growth of parton distributions at small $x$, consistent with experimental data. When applied to three valence quark distributions derived from a quark model, our scheme yields parton distributions that agree well with deep-inelastic scattering data in both large-$x$ and small-$x$ regions, providing a unified description of nucleon structure across the entire $Q^2$ range.

hep-ph↗

arXiv2024

Maximum Entropy Method for Valence Quark Distributions in Exotic Hadrons: A Study of the $Z_c(3900)$ Case

In this study we demonstrate the application of the Maximum Entropy Method (MEM) to determine the valence quark distribution of exotic hadrons. Our investigation yields three key findings. Firstly, we observe a significant shift towards smaller Bjorken scale $x$ in the peak position of the valence quark distribution for hadrons with an increasing number of valence quarks, consistent with previous results by Kawamura and Kumano. Secondly, assuming that the $Z_c(3900)$ initially consists of four valence quarks, we employ MEM to determine its initial valence quark distribution, estimating a radius of $r_c=1.276$ fm at an extremely low resolution scale $Q^2$. Furthermore, we identify a notable discrepancy between our computed charge form factor $G_c(q)$ at leading order and the outcomes of hadron molecular state calculations. We propose that this form factor can be extracted from the QCD counting rule cross-section, which is grounded in Generalized Distribution Amplitudes (GDA) linked to the multi-quark states.

hep-ph↗

arXiv2024

Gluon distributions and mass decompositions of the pion and kaon

We present the gluon distribution functions of pion and kaon in small-$x$ and large-$x$ regions, and compare them with the results obtained from lattice QCD and continuum Schwinger function methods. Whether in the small-$x$ region or the large-$x$ region, our gluon distribution of pion is consistent with the results of lattice QCD and continuum Schwinger function method. In addition, the first four moments of gluon distributions of pion and kaon at different $Q^{2}$ scales are calculated. Furthermore, we present the mass decompositions of pion and kaon with the dynamical parton distribution functions calculated by the DGLAP equation with parton-parton recombination corrections. The mass structures of pion and kaon are totally different from that of the proton.

hep-ph↗

arXiv2023

Exploring the Mass Radius of $^4$He and Implications for Nuclear Structure

In this study, we determine the mass radius of $^4$He, a very light nucleus, by examining the near-threshold $\phi$-meson photoproduction data of the LEPS Collaboration. To assess the gravitational form factor of $^4$He, we employ multiple models for the mass distribution, including Yukawa-type, exponential, Gaussian, and uniform functions. The mass radius of $^4$He is measured to be $1.70\pm0.14$ fm, which is approximately equal to the charge radius of $^4$He. Surprisingly, in contrast to the findings of the proton, no noticeable discrepancy between the charge radius and the mass radius is noted for the $^4$He nucleus. The proton and neutron distributions within $^4$He are likely to be identical, confirming its regular tetrahedral structure in a new way. We propose exploring the difference between charge and mass radii as a new approach to examine the nuclear structure.

hep-ph↗

arXiv2022

Vector meson-nucleon scattering length $|\alpha_{VN}|$ and trace anomalous energy contribution to the nucleon mass $T_{A}$

Low-energy scattering processes of vector meson and nucleon are an important window for studying non-perturbative QCD. The interaction of vector meson with nucleon, vector meson-nucleon scattering length $|\alpha_{VN}|$, is an important component of the study of hadronic interactions. Nowadays many scattering length values $|\alpha_{VN}|$ have been reported using the recent photoproduction experiment data or quasi data. In addition, the study of trace anomalous energy contribution to the proton mass is also a hot topic in non-perturbative QCD and hadron physics. However, it is difficult to measure proton trace anomalous energy experimentally, and the study of the trace anomaly of proton is still inconclusive. In this study, we established the relationship between the scattering length of the vector meson-proton $|\alpha_{Vp}|$ and the trace anomaly contribution of the proton mass $T_{A}$. With the scattering length values extracted by using the Vector Meson Dominance model, we obtained the trace anomaly contribution of the proton mass $T_{A}$ = (22.8$\%$ $\pm$ 1.2$\%$), which is of similar order of magnitude as the 23$\%$ given by Lattice QCD calculation. We conjecture that the trace anomaly contribution of nucleon is independent of the type of vector meson probe. We hope that high precision measurements of vector meson-nucleon scattering length could give us a better chance to explore the origin of the nucleon mass.

hep-ph↗

arXiv2022

Extraction of $\omega$n, $\omega$p and $\phi$N scattering lengths from $\omega$ and $\phi$ differential photoproduction cross sections on the deuterium target

In this study, we try to extract $\omega n$, $\omega p$ and $\phi$N scattering lengths from the differential cross-section data of near-threshold $\omega$ and $\phi$ photoproductions not only to the energy at threshold t$_{thr}$, but also in t to t = 0. The incoherent data of $\omega$ and $\phi$ photoproductions on deuterium target for scattering length extractions are provided by CBELSA/TAPS Collaboration and LEPS Collaboration respectively, where the deuteron is usually approximated as a weakly bound state of a quasi-free neutron plus a quasi-free proton. Under the Vector Meson Doninance model and the assumption of energy independence of the differential cross-section, we obtained the $|\alpha_{\omega n^{*}}|$ and $|\alpha_{\omega p^{*}}|$ of loosely bound neutron and proton in the deuteron to be 0.709 $\pm$ 0.078 fm and 0.621 $\pm$ 0.022 fm respectively at threshold t$_{thr}$ (1.258 $\pm$ 0.130 fm and 1.056 $\pm$ 0.032 fm respectively in t to t = 0) for the first time by fitting the near-threshold data of $\gamma$d $\rightarrow$ $\omega$n(p) and $\gamma$d $\rightarrow$ $\omega$p(n). For a comparison study, we also extracted the scattering length $|\alpha_{\omega p}|$ of the free proton from the $\omega$ photoproduction on the hydrogen target by CBELSA/TAPS Collaboration. With the near-threshold and incoherent $\phi$ photoproduction data of $\gamma$d $\rightarrow$ $\phi$pn by LEPS Collaboration, we obtained scattering length $|\alpha_{\phi N}|$ of the bound nucleon inside the deuteron to be 0.109 $\pm$ 0.008 fm at threshold t$_{thr}$ and 0.276 $\pm$ 0.010 fm in t to t = 0, respectively. The obtained $|\alpha_{\omega p}|$ and $|\alpha_{\phi N}|$ are basically in agreement with the experimental indications and the theoretical predictions within the current uncertainties.

hep-ph↗

arXiv2022

Pion parton distribution functions with the nonrelativistic constituent quark model

We calculate the valence quark distribution functions of the $\pi$ meson using the non-relativistic chiral constituent quark model. The $\pi$ wave function is obtained by solving the two-body Schr\"odinger equation within the framework of constituent quark model. We transform the $\pi$ wave function from the rest frame to the light cone or infinite momentum frame based on the Lorentz boost. The valence quark distributions at the initial evolution scale are obtained. The QCD evolution are given with the DGLAP equations with parton-parton recombination corrections. With tuning the valence up (down) quark mass to 70 MeV, the calculated valence up quark distributions at $Q^2=20$ GeV$^2$ are in good agreement with the E615 experimental data. The structure functions $\rm{F}_2^\pi(x,Q^2)$ of pion are also calculated which consist with the H1 experimental data. The proposed mechanisms here could be also used to study other hadrons.

hep-ph↗

arXiv2022

High $Q^2$ Behavior of the Proton Structure Function through the Balitsky-Kovchegov Equation

Numerous experimental and theoretical investigations have highlighted the power law behavior of the proton structure function $ F_2(x, Q^2) $, particularly the dependence of its power constant on various kinematic variables. In this study, we analyze the proton structure function $ F_2 $ employing the analytical solution of the Balitsky-Kovchegov equation, with a focus on the high $ Q^2 $ regime and small $ x $ domains. Our results indicate that as $ Q^2 $ increases, the slope parameter $ \lambda $, which characterizes the growth rate of $ F_2 $, exhibits a gradual decrease, approaching a limiting value of $ \lambda \approx 0.41 \pm 0.01 $ for large $ Q^2 $. We suggest that this behavior of $ \lambda $ may be attributed to mechanisms such as gluon overlap and the suppression of phase space growth. To substantiate these conclusions, further high-precision electron-ion collision experiments are required, encompassing a broad range of $ Q^2 $ and $ x $.

hep-ph↗

arXiv2022

The neutron and proton mass radii from the vector meson photoproduction data on the deuterium target

In this study, we try to extract the mass radii of the neutron and the proton from the differential cross section data of near-threshold $\omega$ and $\phi$ photoproductions on deuterium target, which is often approximated as a quasi-free neutron plus a quasi-free proton. The incoherent data of $\omega$ and $\phi$ photoproductions are provided by CBELSA/TAPS collaboration and LEPS collaboration respectively, where the deuteron is disintegrated in the experiments to measure the properties of individual nucleons. Under the VMD model and the assumption of dipole gravitational form factor, we determined the loosely bound neutron and proton mass radii to be $0.795\pm0.092\rm(stat.)\pm0.073\rm(syst.)$ fm and $0.744\pm0.029\rm(stat.)\pm0.042\rm(syst.)$ fm respectively from the near-threshold data of $\gamma d \rightarrow \omega n (p)$ and $\gamma d \rightarrow \omega p (n)$, for the first time. With the near-threshold and incoherent $\phi$ photoproduction data of $\gamma d \rightarrow \phi p n$, we determined the average mass radius of the bound nucleon (neutron or proton) inside the deuteron to be $0.755\pm0.039\rm(stat.)\pm0.039\rm(syst.)$ fm, for the first time. For a comparison study, we also extracted the mass radius of the free proton from the $\omega$ photoproduction on the hydrogen target by CBELSA/TAPS collaboration. Based on our analysis results under the assumptions of VMD model and a low energy QCD theorem, we find that the neutron mass radius is consistent with the proton mass radius within the current statistical uncertainties, and that the nuclear modification on the nucleon mass radius is small inside the deuteron.

hep-ph↗

arXiv2021

Tackling the kaon structure function at EicC

Measuring the kaon structure beyond the proton and pion structures is one of the hot topics in hadron physics, as it is one way to understand the nature of Nambu-Goldstone boson of QCD and to see the interplay between the EHM mechanism and the HB mechanism for hadron mass generation. In this paper, we present a simulation of the leading $\Lambda$ baryon tagged deep inelastic scattering experiment at EicC (Electron-ion collider in China), which is engaged to unveil the internal structure of kaon through Sullivan process. According to our simulation results, the suggested experiment will cover the kinematical domain of $0.05\lesssim x_{\rm K} \lesssim 0.85$ and $Q^2$ up to 50 GeV$^2$, with the acceptable statistical uncertainties. In the relatively low-$Q^2$ region ($<10$ GeV$^2$), the Monte-Carlo simulation shows a good precision of the measurement ($<5$\%) for the kaon structure function $F_2^{\rm K}$. In the high-$Q^2$ region (up to 50 GeV$^2$), the statistical uncertainty of $F_2^{\rm K}$ is also acceptable ($<10$\%) for the data at $x_{\rm K}<0.8$. To perform such an experiment at an electron-ion collider, a high-performance zero-degree calorimeter is required.

hep-ph↗

arXiv2021

An analysis of polarized parton distribution functions with nonlinear QCD evolution equations

We present the polarized parton distribution functions from a QCD analysis of the worldwide polarized deep inelastic scattering data, based on the dynamical parton distribution model. All the sea quarks and gluons are dynamically generated from QCD radiations, with the nonperturbative input contains only the polarized valence quark distributions. This approach leads to a simple parametrization, which has only four free parameters. In the analysis, we apply the DGLAP equations with parton-parton recombination corrections. The parameterized nonperturbative input at an extremely low $Q_0^2$ reproduces well the spin-dependent structure functions measured at high $Q^{2}$. Comparisons with experimental observations and some other polarized parton distribution functions are also shown. Our results are in good agreement with the experimental data and consistent with some other parameterized models. Furthermore, our analysis gives the positive polarized gluon distribution and it suggests that the gluon distribution plays an important role to the proton spin content. The polarized antiquark distributions are non-zero at high $Q^2$ but quite small compared to polarized valence quark distribution, based on this dynamical parton model analysis. This analysis shows smaller statistical uncertainties for the polarized sea quark and gluon distributions, thanks to the fewer free parameters used for the parametrization of the initial polarized PDFs.

hep-ph↗

arXiv2021

Proton and deuteron mass radii from near-threshold $\phi$-meson photoproduction

We analyze the exclusive $\phi$-meson photoproduction on both hydrogen and deuterium targets based on the published data of CLAS, SAPHIR and LEPS collaborations. A dipole-form scalar gravitational form factor is applied to describe the $|t|$-dependence of the differential cross section. Based on the average of all the near-threshold data from CLAS, SAPHIR and LEPS, we find that the proton and deuteron mass radii are $0.75 \pm 0.02$ fm and $1.95 \pm 0.19$ fm respectively. The coherent and near-threshold quarkonium photoproduction seems to be sensitive to the radius of the hadronic system. The vector-meson-dominance model together with a low-energy QCD theorem well describe the data of near-threshold $\phi$ photoproduction on the hadronic systems.

hep-ph↗

arXiv2021

Proton Shell Structure

We study the internal structure of the proton and propose a shell structure model of the proton. Based on the mass distribution and mass radius of proton we analyze the experiments at different energy scales and conclude that there should be shell structure inside proton, and the quark and gluon shells are energy-scale-dependent. We successfully explain the dip-like structure in the proton-proton elastic scattering cross section distribution from TOTEM Collaboration using the mass decomposition of proton and the proton shell structure at different energy scales.

hep-ph↗

arXiv2021

Electron-Ion Collider in China

Lepton scattering is an established ideal tool for studying inner structure of small particles such as nucleons as well as nuclei. As a future high energy nuclear physics project, an Electron-ion collider in China (EicC) has been proposed. It will be constructed based on an upgraded heavy-ion accelerator, High Intensity heavy-ion Accelerator Facility (HIAF) which is currently under construction, together with a new electron ring. The proposed collider will provide highly polarized electrons (with a polarization of $\sim$80%) and protons (with a polarization of $\sim$70%) with variable center of mass energies from 15 to 20 GeV and the luminosity of (2-3) $\times$ 10$^{33}$ cm$^{-2}$ s$^{-1}$. Polarized deuterons and Helium-3, as well as unpolarized ion beams from Carbon to Uranium, will be also available at the EicC. The main foci of the EicC will be precision measurements of the structure of the nucleon in the sea quark region, including 3D tomography of nucleon; the partonic structure of nuclei and the parton interaction with the nuclear environment; the exotic states, especially those with heavy flavor quark contents. In addition, issues fundamental to understanding the origin of mass could be addressed by measurements of heavy quarkonia near-threshold production at the EicC. In order to achieve the above-mentioned physics goals, a hermetical detector system will be constructed with cutting-edge technologies. This document is the result of collective contributions and valuable inputs from experts across the globe. The EicC physics program complements the ongoing scientific programs at the Jefferson Laboratory and the future EIC project in the United States. The success of this project will also advance both nuclear and particle physics as well as accelerator and detector technology in China.

nucl-ex↗