Welcome

• 黄性涛

Towards a first principles light-front Hamiltonian for the nucleon

• Xingbo Zhao (Institute of Modern Physics, Chinese Academy of Sciences)

We solve the light-front QCD Hamiltonian including, for the first time, gluons and sea quarks along with the valence quarks. Our fully relativistic, nonperturbative approach accurately describes the proton’s mass, electromagnetic form factors, axial and tensor charges, and Parton Distribution Functions (PDFs) at a defined scale. It highlights the impact of dynamical gluons and sea quarks on proton structure, contributing to a unified framework for hadron distributions in both longitudinal and transverse momentum space. This work also offers predictive power for experimentally accessible Generalized Parton Distributions (GPDs), Transverse Momentum Distributions (TMDs), among other observables, with potential applications to other hadrons and nuclei.

Fragmentation function at low energy e+e-

• Wenbiao Yan

Probing gluon and strange quark helicity distributions in the proton at STAR

• Yi Yu (Shandong University)

Unraveling the proton spin composition, comprising intrinsic spins and orbital angular momenta of quarks and gluons, stands as one of the most fundamental and challenging questions in QCD. Tremendous progress has been made since the first surprising result by the EMC experiment in the late 1980s, which significantly contribute to our understanding of this question. However, the helicity distributions of strange quarks and anti-quarks are still not well constrained by the experimental data. Measurement of the longitudinal double spin asymmetry, $A_{LL}$, of $\Lambda$, $\overline{\Lambda}$ and $K_S^0$ in the longitudinally polarized proton-proton collisions may shed light on the strange quark and anti-quark helicity distributions. In addition, measuring the longitudinal spin transfer $D_{LL}$ of $\Lambda$ and $\overline{\Lambda}$ is not only sensitive to the helicity distribution of strange quark but can also shed light on the polarized fragmentation functions. Meanwhile, $A_{LL}$ of the inclusive jets tagged with a $\pi^+/\pi^-$ carrying high jet momentum fraction, $z$, in proton-proton collisions can provide further constraints on the gluon helicity distribution in the proton. In this talk, we will present the results of the $A_{LL}$ for $\Lambda$, $\overline{\Lambda}$ and $K_S^0$, and the inclusive jets tagged with a high-$z$ $\pi^{\pm}$ and the measurements of $D_{LL}$ for $\Lambda$ and $\overline{\Lambda}$. These results are based on the longitudinally polarized proton-proton collisions at $\sqrt{s}=200$ $\rm{GeV}$ collected by the STAR experiment with an integrated luminosity of about 52 $\rm{pb^{-1}}$.

Azimuthal transverse single-spin asymmetries of inclusive jets and hadrons within jets from polarized ${pp}$ collisions at RHIC-STAR

• Yixin Zhang (Shandong University)

The study of the origins of transverse single-spin asymmetries has stimulated significant progress in the development of twist-3 formalism and transverse-momentum-dependent parton distribution functions (TMDs). Measurements of the azimuthal distribution of inclusive jets and identified hadrons within jets produced in transversely polarized hadronic interactions provide key insights into TMD physics. In particular, measurements of the Collins effect, which involves the interplay between the quark transversity and Collins fragmentation function, provide access to the final-state phenomena of TMD physics. This talk will report measurements of transverse single-spin asymmetries for inclusive jets and hadrons within jets, obtained in recent years at RHIC-STAR. In particular, the polarized $pp$ collision dataset taken in 2017, with an integrated luminosity of 320 $\mathrm{pb}^{-1}$, has significantly improved the precision of these measurements. The comparison of Collins asymmetries between ${pp}$ collisions at 200 GeV and 510 GeV can provide crucial insights into the TMD evolution of the Collins function. Additionally, comparing experimental results from ${pp}$ collisions with theoretical predictions derived from global fits to semi-inclusive deep inelastic scattering and $e^+e^-$ annihilation data will allow tests of the universality of Collins effect.

Pion Boer-Mulders function using a contact interaction

• 丹丹 程 (Nanjing University)

A symmetry preserving treatment of a vector ⊗ vector contact interaction (SCI) is used as the basis for calculations of the two pion transverse momentum dependent parton distribution functions (TMDs); namely, that for unpolarised valence degrees-of-freedom and the analogous Boer-Mulders (BM) function. Amongst other things, the analysis enables the following themes to be addressed: the quark current mass dependence of pion TMDs; the impact of the gauge link model on the positivity constraint that bounds the BM function relative to the unpolarised TMD; the equivalence of direct diagrammatic and light-front wave function TMD calculations; and the size of the BM shift. Interpreted astutely, these SCI results enable one to draw insightful pictures of pion TMDs.

Contact interaction study of proton parton distributions

• Yang Yu (Nanjing University)

Using a symmetry-preserving formulation of a vector × vector contact interaction (SCI) and treating the proton as a quark + interacting-diquark bound state, whose structure is obtained by solving a Poincaré-covariant Faddeev equation, we provide a comprehensive, coherent set of predictions for unpolarised and polarised proton parton distribution functions(DFs): valence, glue, and four-flavour separated sea. The results enable many themes to be addressed, including: the asymmetry of antimatter in the proton; the neutron:proton structure function ratio; helicity retention in hard scattering processes; the charm quark momentum fraction; the sign and size of the polarised gluon DF; and the origin of the proton spin. In all cases where sound analyses of data are available, SCI predictions are semiquantitatively in agreement with the results. Those mismatches which exist are typically attributable to the momentum-independence of the underlying interaction. Judiciously interpreted, the SCI delivers a sound and insightful explanation of proton structure as expressed in DFs.

Transverse momentum dependent helicity distributions

• Ke Yang (Peking University)

In this talk, I will present the first extraction of TMD helicity distributions, by analyzing double spin asymmetry data from SIDIS.

The phenomenological extraction of Sivers and transversity distribution functions

• Hongxin Dong (南京师范大学)

We will present the phenomenological extraction of Sivers and transversity distribution functions and Collins fragmentation functions by simultaneously fitting to semi-inclusive deep inelastic scattering (SIDIS) and electron-positron annihilation data. In addition, we investigate the impact of future SIDIS data from EicC on the extraction of TMDs.

Global analysis of Sivers and Collins asymmetries within TMD factorization

• 春华 曾 (Institute of Modern Physics)

In this letter we present a global analysis of Sivers function, transversity distribution functions and Collins fragmentation functions within TMD factorization. This analysis encompasses the latest data sets from semi-inclusive deep inelastic scattering, Drell-Yan, and $W^{\pm}/Z$-boson production as recently reported by the COMPASS and STAR Collaborations. Upon integrating this new data into our fitting, the accuracy of the $d$ quark extraction for both transversity and Sivers distribution is notably improved.

pion and kaon fragmentation functions

• 惠瑜 邢 (南京大学)

Using the crossing symmetry in quantum field theory, the pion and kaon fragmentation functions (FFs) can be predicted. These are the first QCD prediction for pion and kaon FFs. In this way, a unified treatment of distribution functions and FFs was accomplished. The calculated FFs are compared the existing fits, and they are useful for the future data collection and anticipated facilities.

Lattice QCD calculation of the unpolarized transverse-momentum-dependent parton distributions

• 其安 张 (北京航空航天大学)

We present a first lattice QCD calculation of the unpolarized nucleon’s isovector transverse-momentumdependent parton distribution functions (TMDPDFs), which are essential to predict observables of multiscale, semi-inclusive processes in the standard model. We use a $N_f=2+1+1$ MILC ensemble with valence clover fermions on a highly improved staggered quark (HISQ) sea to compute the quark momentum distributions in a large-momentum nucleon on the lattice. The state-of-the-art techniques in renormalization and extrapolation in the correlation distance on the lattice are adopted. The perturbative kernel up to next-to-next-to-leading order is taken into account, and the dependence on the pion mass and the hadron momentum is explored. Our results are qualitatively comparable with phenomenological TMDPDFs, which provide an opportunity to predict high energy scatterings from first principles.

Transverse-momentum-dependent wave functions for pion and soft functions at one-loop in large momentum effective theory

• Jun Zeng (Shanghai Jiao Tong University)

In large-momentum effective theory (LaMET), the transverse-momentum-dependent (TMD) light-front wave functions and soft functions can be extracted from the simulation of a four-quark form factor and equal-time correlation functions. In this work, using expansion by regions we provide a one-loop proof of TMD factorization of the form factor. For the one-loop validation, we also present a detailed calculation of ${\mathcal O}(\alpha_s)$ perturbative corrections to these quantities, in which we adopt a modern technique for the calculation of TMD form factor based the integration by part and differential equation. The one-loop hard functions are then extracted. Using lattice data from Lattice Parton Collaboration on quasi-TMDWFs, we estimate the effects from the one-loop matching kernel and find that the perturbative corrections depend on the operator to define the form factor, but are less sensitive to the transverse separation. These results will be helpful to precisely extract the soft functions and TMD wave functions from the first-principle in future.

Electron-ion collider in China

• Jinlong Zhang

Probing quark and gluon orbital angular momentum at EIC and EicC

• 杜鑫 郑 (山东高等技术研究院)

We propose to detect signals from quark and gluon orbital angular momentum (OAM) through exclusive $\pi^0$ production in electron-(longitudinally-polarized) proton collisions. Our analysis demonstrates that the $\sin 2\phi$ azimuthal angular correlation between the transverse momentum of the scattered electron and the recoil proton serves as a sensitive probe of quark and gluon OAM. Additionally, we present a numerical estimate of the asymmetry associated with this correlation for the kinematics accessible at EIC and EicC. This study aims to pave the way for the first experimental study of parton OAM in relation to the Jaffe-Manohar spin sum rule

Study of GPD via meson production in electron-proton scattering

• Ya-Ping Xie (IMP, CAS)

We study GPDs through pseudoscalar and vector meson production in electron-proton scattering.

Higher-twist generalized parton distributions of the pion and kaon at zero skewness in the light-cone quark model

• 晓燕 栾 (东南大学)

We investigate the higher-twist generalized parton distributions (GPDs) of the pion and kaon at zero skewness by adopting the overlap representation within the light-cone formalism. Using the wave functions of pion and kaon deduced from a light-cone quark model (LCQM), we calculate the twist-3 and twist-4 GPDs $E_{2}(x,0,t)$, $G_{2}(x,0,t)$, $F_{3}(x,0,t)$ and $H_{3}(x,0,t)$ for the pion and kaon mesons. Numerical results for these higher-twist GPDs of valence quark and antiquark are presented. By taking the forward limit, we also present the numerical results for the corresponding twist-3 and twist-4 parton distribution functions (PDFs) $e(x)$ and $f_{3}(x)$ of pion and kaon. We further study the relations between $e(x)$ or $f_{3}(x)$ and the twist-2 unpolarized PDF $f_{1}(x)$.

Gluon imaging via azimuthal correlations in time-like Compton scattering

• Hao-Cheng Zhang (Shandong University)

GTMDs (Generalized transverse momentum distributions) are important non-perturbative inputs to depict the 3-dimensional structure of nucleons. We propose the method to access small-x gluon GTMDs from lepton-pair azimuthal angle dependence in time-like Compton scattering using Golec-Biernat-Wüsthoff model, which is parallel to the study in deeply virtual Compton scattering.

旁观者模型中对T-odd横动量依赖的胶子碎裂函数的研究

• 修鹏 谢 (东南大学)

我们提出了一种用于计算末态是自旋为1/2的强子的T-odd横动量依赖的胶子碎裂函数的模型。我们的模型是基于一个类时不在壳的胶子能碎裂成一个强子和一个在壳的旁观者粒子。为了考虑胶子交换的效应，我们计算了胶子-胶子关联函数的所有可能的单圈图。四个图中有两个图对碎裂函数产生了贡献。我们给出了T-odd横动量依赖胶子碎裂函数的解析表达式，并且给出了碎裂函数对$z$和$k_T$依赖关系的数值结果。

Transverse spin correlation in unpolarized collisions

• Lei Yang

Higher twist effects: Transverse color Lorentz force inside proton from BLFQ

• Xingbo Zhao