Effects of QCD Vacuum and the Instanton Induced-Contributions to the Nucleon Structure Functions

The instanton induced cross section in deep inelastic kinematics is a subject which people are tendentious to investigate it. Instanton induced contributions are well defined for the nucleon structure function. The non-perturbative contribution to the quark distributions of structure function, F2（x, Q2）, is considered within an instanton model for the QCD vacuum. We find that the structure function may possess numerically large non-perterbative contributions which are related to the violation of chirality and correspond to the correction of parton distribution of the leading twist. It is shown that the instantons give a negative contribution to the structure function at the NLO approximation. A comparison between our results, considering instantaon effect, and the case when we do not take this effect is done. Taking into account the instanton size, p, via the modified running coupling constant we get to a good agreement between our results at the NLO and NNLO approximations and the available experimental data, specially at the low values of the Bjorken variable x 〈 0.1 which confirms the validity of our calculations.

Quark distributions in nuclei and nuclear effects on nucleon structure functions

Extended quark distribution functions are presented obtained by fitting a large amount of experimental data of the l-A DIS process on the basis of an improved nuclear density model. The experimental data of l-A DIS processes with A≥ 3 in the region 0.0010 ≤ x ≤ 0.9500 are quite satisfactorily described by using the extended formulae. Our knowledge of the influence of nuclear matter on the quark distributions is deepened.

Nucleon Spin Structure Functions in the Resonance Region and the Duality

We discuss the nucleon spin structure function g1 and the difference between the proton and neutron targets , based on quark model calculation. Quark-hadron duality for the nucleon spin structure function is also analyzed. Effects of the Δ(1232) and Roper P11(1440) resonances on the spin structure function and on the difference are mentioned. The results of different models for the Roper resonance are also addressed.

Bloom-Gilman Duality of Nucleon Spin Structure Function and Elastic Peak Contribution

By employing the parametrization form of the nucleon spin structure functionin the resonance region, which includes the contributions of the resonance peaks and of nonresonancebackground, we study Bloom—Oilman quark-hadron duality of g_1 both in the inelastic resonanceregion and elastic one.

Lambda polarization at the Electron-ion collider in China

Lambda polarization can be measured through its self-analyzing weak decay, making it an ideal candidate for studying spin effects in high-energy scattering. In lepton-nucleon deep inelastic scattering(DIS), Lambda polarization measurements can probe polarized parton distribution functions(PDFs) and polarized fragmentation functions(FFs). One of the most promising facilities for high-energy nuclear physics research is the proposed Electron-ion collider in China(EicC). As a next-generation facility, EicC is set to advance our understanding of nuclear physics to new heights. In this article, we study the Lambda production in electron-proton collisions at the EicC energy, in particular the reconstruction of Lambda based on the performance of the designed EicC detector. In addition, taking spontaneous transverse polarization as an example, we provide a theoretical prediction with a statistical projection based on one month of EicC data, offering valuable insights into future research prospects.

Recent results on nucleon spin structure study at RHIC

Both the PHENIX and STAR experiments at the Relativistic Heavy Ion Collider （RHIC） at Brookhaven National Laboratory are running polarized proton-proton collisions at √s = 200 and 500 GeV. The main goal of the RHIC spin physics program is to gain deeper insight into the spin structure of the nucleon. We will give an overview of recent spin results from RHIC, particularly the study of gluon polarization via jet/hadron production and sea quark polarization via W boson production in longitudinally polarized proton-proton collisions.

Gauge invariance and quantization applied to atom and nucleon internal structure

The prevailing theoretical quark and gluon momentum,orbital angular momentum and spin operators,satisfy either gauge invariance or the corresponding canonical commutation relation,but one never has these operators which satisfy both except the quark spin.The conflicts between gauge invariance and the canonical quantization requirement of these operators are discussed.A new set of quark and gluon momentum,orbital angular momentum and spin operators,which satisfy both gauge invariance and canonical momentum and angular momentum commutation relation,are proposed.To achieve such a proper decomposition the key point is to separate the gauge field into the pure gauge and the gauge covariant parts.The same conflicts also exist in QED and quantum mechanics,and have been solved in the same manner.The impacts of this new decomposition to the nucleon internal structure are discussed.

Nucleon internal structure: a new set of quark, gluon momentum, angular momentum operators and parton distribution functions

It is unavoidable to deal with the quark and gluon momentum and angular momentum contributions to the nucleon momentum and spin in the study of nucleon internal structure. However we never have the quark and gluon momentum, orbital angular momentum and gluon spin operators which satisfy both the gauge invariance and the canonical momentum and angular momentum commutation relation. The conflicts between the gauge invariance and canonical quantization requirement of these operators are discussed. A new set of quark and gluon momentum, orbital angular momentum and spin operators, which satisfy both the gauge invariance and canonical momentum and angular momentum commutation relation, are proposed. The key point to achieve such a proper decomposition is to separate the gauge field into the pure gauge and the gauge covariant parts. The same conflicts also exist in QED and quantum mechanics and have been solved in the same manner. The impacts of this new decomposition to the nucleon internal structure are discussed.

Nucleon/nuclei polarized structure function,using Jacobi polynomials expansion

We use the constituent quark model to extract polarized parton distributions and finally polarized nucleon structure function.Due to limited experimental data which do not cover whole （x,Q 2 ） plane and to increase the reliability of the fitting,we employ the Jacobi orthogonal polynomials expansion.It will be possible to extract the polarized structure functions for Helium,using the convolution of the nucleon polarized structure functions with the light cone moment distribution.The results are in good agreement with available experimental data and some theoretical models.

Recent results on nucleon resonance electrocouplings from the studies of π^+π^-p electroproduction with the CLAS detector

Recent results on nucleon resonance studies in π＋π-p electro- production off protons with the CLAS detector are presented. The analysis of CLAS data allowed us to determine all essential contributiag mechanisms, providing a credible separation between resonant and non-resonant parts of the cross sections in a wide kinematical area of invariant masses of the final hadronic system 1.3 〈 W 〈 1.8 GeV and photon virtutualities 0.2 〈 Q2 〈 1.5 GeV2. Electrocouplings of several excited proton states with masses less than 1.8 GeV were obtained for the first time from the analysis of π＋π-p exclusive electroproduction channel.

The time-reversal odd side of a jet

We re-examine the jet probes of the nucleon spin and flavor structures.We find for the first time that the time-reversal odd(T-odd)component of a jet,conventionally thought to vanish,can survive due to the non-perturbative fragmentation and hadronization effects.This additional contribution of a jet will lead to novel jet phenomena relevant for unlocking the access to several spin structures of the nucleon,which were thought to be impossible by using jets.As examples,we show how the T-odd constituent can couple to the proton transversity at the Electron Ion Collider(EIC)and can give rise to the anisotropy in the jet production in e^(+)e^(-) annihilations.We expect the T-odd contribution of the jet to have broad applications in high energy nuclear physics.

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 po-larization of 80%)and protons(with a polarization of 70%)with variable center of mass energies from 15 to 20 GeV and the luminosity of(2–3)×1033 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.

Highlights from the COMPASS experiment

The Compass experiment at CERN is studying the nucleon spin structure with a 160 GeV polarized muon beam and polarized targets as well as hadron structure with 190 GeV pion,kaon and proton beams.The paper gives an overview of the results for the helicity and transverse spin structure of the nucleon.A first result from the spectroscopy experiments,the observation of a resonance with exotic J P C = 1-＋ quantum numbers at 1660 MeV is also presented.The paper ends with an outlook to future measurements.

Form factor measurements with ANDA at FAIR

The high intensity and high energy antiproton beams which will be produced at FAIR open the possibility to determine time-like electromagnetic form factors in a wide kinematical range, through the annihilation reaction： p ＋ p → e^＋ ＋ e^-. The status of the proposed experiment as well as the expected results are presented on the basis of realistic simulations. The impact of these measurements on the understanding of the nucleon structure, of the asymptotic properties of form factors and of the reaction mechanism are discussed using model independent statements based on symmetry properties of the strong and electromagnetic interactions in connection with space-like data.

Deeply virtual compton scattering at HERMES

Generalized Parton Distributions （GPDs） provide a way to access total angular momenta of partons and give a multidimensional picture of the nucleon structure.Deeply Virtual Compton Scattering （DVCS） is the most direct exclusive process to study GPDs.Different azimuthal cross-section asymmetries with respect to beam helicity,beam charge,and target polarization have been measured in the HERMES experiment.A recoil detector was installed at HERMES to directly detect the recoil proton.

TMDs studied in semi-inclusive deep inelastic scattering at HERMES

The HERMES measured azimuthal amplitudes of cross sections and their transverse target single spin asymmetries for hadron productions in semi-inclusive deep inelastic scattering.From the extracted amplitudes,novel parton distribution functions can be studied.The recent results related to Sivers and Boer-Mulders distribution functions are discussed.

Single π0electro-production in the resonance region with CLAS＊

We report the analysis status of single π0electroproduction in the resonance region to study the electromagnetic excitation of the nucleon resonances. The study is aimed at understanding of the internal structure and dynamics of the nucleon. The experiment was performed using an unpolarized cryogenic hydrogen target and 2.0 and 5.8 GeV polarized electron beam during the ele and e1-6 run periods with CLAS at Jefferson Lab. The new measurements will produce a data base with high statistics and large kinematic coverage for the hadronic invariant mass （W） up to 2.0 CeV in the momentum transfer （Q2） range of 0.3--6.0 GeV2. Preliminary results will be presented and compared with the various model calculations.

Exclusive π^(0) production at EIC of China within handbag approach

Exclusive π^(0) electroproduction is analyzed within the handbag approach based on Generalized Parton Distribution(GPDs)factorization.We consider the leading-twist contribution together with the transversity effects.It is shown that the transversity GPDs H_(T) and E_(T) are essential in the description of the π^(0) cross section.Predictions for the future Electron-Ion Collider of China(EicC)energy range are provided.It is found that transversity dominanceσ_(T)>>σ_(L),observed at low energies,is valid up to the EicC energy range.