Sigma Meson Production in Nuclear Reactions

The sigma meson production in p ＋ ^12C and p A- ^40Ca reactions at the incident energy Ep = 1.5 GeV is investigated within the Quantum Molecular Dynamics model. The simulation results indicate a distinctive A dependence of the sigma production, that is, the increase of A is followed by an increase of the production cross sections. We find that the σ meson production in proton-induced reactions is strongly medium-dependent, and the produced σ mesons decaying in a denser medium experience a stronger mass shift towards lower masses. This mass shift is an experimentally accessible observable in the final state pion pairs, which do not suffer from reabsorption by the surrounding nucleons. It is pointed out that the ratio of measured sigma cross sections as a function of the sigma invariant-mass from various reactions is a good probe to explore the existence of the σ meson in a dense nuclear environment.

Energy Dependence of String Fragmentation Function and Ф Meson Production

The meson productions in Au+Au and/or Pb+Pb collisions at AGS, SPS, RHIC, and LHC energies have been studied systematically with a hadron and string cascade model LUCIAE. After considering the energy dependence of the model parameter α in string fragmentation function and adjusting it to the experimental data of charged multiplicity to a certain extent, the model predictions for meson yield, rapidity, and transverse mass distributions are compatible with the experimental data at AGS, SPS and RHIC energies. A calculation for Pb+Pb collisions at LHC energy is given as well. The obtained fractional variable in string fragmentation function shows a saturation in energy dependence. It is discussed that the saturation of fractional variable in string fragmentation function might be a qualitative representation of the energy dependence of nuclear transparency.

Charmed Meson Production in Deep Inelastic e+A Scattering at Small_(-x)

Based on the nuclear effects considered in the Glauber-Gribov approach,charmed meson production inhigh energy deep inelastic e+A scattering is investigated in the color dipole formalism.Using the Peterson fragmentationfunction and the KLR-AdS/CFT color dipole model,which reasonably well describes the HERA data for the inclusivestructure functions at small Bjorken-x,we present the predictive results for the D-meson transverse spectra at EIC andLHeC energies.The theoretical results indicate that the x-independence phenomena at very small-x predicted by theKLR-AdS/CFT model are not seen in our calculation.

Extraction of resonance parameters from meson production reaction

We have developed an analytic continuation method for extracting parameters of nucleon resonances within a Hamiltonian formulation of meson-nucleon reactions. The method was tested for simple solvable models and then applied for our recent coupled channels model （πN, ηN, π△, ρN, and σN ） of the π＊N and γ＊N reactions. The resonance pole positions and their properties are studied for P11and P11 channels.

Exclusive vector meson production with the analytical solution of Balitsky-Kovchegov equation

Exclusive vector meson production is an excellent probe for describing the structure of protons.In this study,based on the dipole model,the differential cross sections,total cross sections,and ratios of the longitudinal to transverse cross section of the J/ψandρ^(0)productions are calculated with the analytical solution of the Balitsky-Kovchegov(BK)equation.In addition,we consider the influences of two meson wave function models on the results.Our predictions,which are slightly sensitive to meson wave functions,agree with the experimental data.The analytical solution of the BK equation is reliable for description of exclusive vector meson productions in a certain range of Q^(2).

Near-threshold K^*(892)^+ meson production in the interaction of π−mesons with nuclei

We study the inclusive production of strange vector K^∗(892)^+ mesons in π−A reactions at near-threshold laboratory incident pion momenta of 1.4-2.0 GeV/c via a nuclear spectral function approach.The approach accounts for incoherent primary π−meson-proton π−p→K^∗(892)^+Σ^− production processes as well as the influence of the scalar K^∗(892)^+-nucleus potential(or the K^∗(892)^+ in-medium mass shift)on these processes.We calculate the absolute differential and total cross sections for the production of K∗(892)+mesons from carbon and tungsten nuclei at laboratory angles of 0∘-45∘and at the aforementioned momenta in five scenarios for the aforenoted shift.We show that the K^∗(892)^+ momentum distributions and their excitation functions(absolute and relative)possess a high sensitivity to changes in the in-medium K^∗(892)^+ mass shift in the low-momentum region of 0.1-0.6 GeV/c.Therefore,the measurement of such observables in a dedicated experiment at the GSI pion beam facility in the near-threshold momentum domain will allow us to get valuable information on the K^∗(892)^+ in-medium properties.

Exclusive meson production at HERMES

The exclusive electroproduction of pseudoscalar and vector mesons was studied with the HERMES spectrometer at the DESY laboratory by scattering 27.6 GeV positron and electron beams off a transversely polarized hydrogen target.The results are compared to calculations based on generalized parton distributions,some of which are sensitive to the contribution of the total angular momentum of the quarks to the proton spin.

Study of transversity GPDs from pseudoscalar mesons production at EIC of China

The exclusive η and π^(0)electroproduction is studied in the handbag approach based on the generalized parton distributions(GPDs)factorization.Predictions of π^(0)and η mesons are calculated for future electron-ion collider in China(EicC)energy ranges,using obtained cross sections we extract information on the transversity GPDs contributions to these processes.

Exclusive photoproduction of vector meson at next-to-leading order from color glass condensate

The exclusive photoproduction of vector mesons(J/ψ/andφ)is investigated by considering the next-toleading order corrections in the framework of the color glass condensate.We compare the next-to-leading order modified dipole amplitude with the HERA data,finding a good agreement.Our studies show that theχ~2/d.o.f from the leading order,running coupling,and collinearly improved next-to-leading order dipole amplitudes are 2.159,1.097,and 0.932 for the elastic cross-section,and 2.056,1.449,and 1.357 for the differential cross-section,respectively.The results indicate that the higher-order corrections contribute significantly to the vector meson productions,and the description of the experimental data is dramatically improved once the higher order corrections are included.We extend the next-to-leading order exclusive vector meson production model to LHC energies using the same parameters obtained from HERA.We find that our model provides a rather good description of the J/ψandΦdata in proton-proton collisions at 7 TeV and 13 TeV in LHCb experiments.

Meson-production experiments at COSY-Jülich

Selected results from experiments at COSY-Jülich are presented： an attempt to measure the mass of the η meson with high precision （ANKE facility）,first steps towards the detection of rare η decays （WASA）,and several measurements of KK-pair production （ANKE,COSY-11,MOMO）.

Analysis of the interaction between theφmeson and nucleus

In this study,we systematically investigate theφmeson and nucleus interaction by analyzing and fitting the cross sections ofγN→φN reactions near the threshold,where N represents the nucleus.Using the vector meson dominant model,the distribution of theφ-N scattering length is presented as a function of energy,and the results show that there is a slight increase in scattering length with increasing energy.Based on this,the average scattering length of aφ-proton is obtained as 0.10±0.01 fm by combining experimental data and theoretical models.Moreover,the average scattering length of theφ-deuteron interaction is derived to be 0.014±0.002 fm for the first time.Furthermore,the effect of the momentum transfer|tmin|on theφ-N scattering length at the threshold is discussed.The obtained results not only provide important theoretical information for a more comprehensive and accurate study of theφ-N scattering length,but also a basis for future experimental measurements ofφmeson production.

Exclusive and dissociative J/ψproduction with collinear-improved Balitsky-Kovchegov equation

We extend the hotspot model to include the virtuality dependence and use it to study the exclusive and dissociative J/Ψ production combined with the dipole amplitude in the target rapidity representation.We determined that virtuality takes effect on a number of hotspots,thus providing a better description of the J/Ψ production data at HERA.The collinear improved Balitsky-Kovchegove equation in the target rapidity representation is numerically solved and used to fit the J/Ψ experimental data with a series of hotspot sizes.We infer that virtuality significantly influences the number and size of hotspots.The expression χ^(2)/d.o.f=1.0183 resulting from the fit with the collinear improved dipole amplitude in the target rapidity representation is more reasonable than the correspondingχ^(2)/d.o.f=1.3995 originating from the leading order fit,which indicates that the collinear improved evolution equation in the target rapidity representation can provide a relatively good depiction of the exclusive and dissociative HERA data.

η-production on the proton via electromagnetic and hadronic probes

The reactions π-p →ηn and γ＇p →ηP are investigated within a dynamical coupledJchannels model of meson production reactions in the nucleon resonance region. The meson-baryon channels included are πN, ηN, π△, σN, and pN. The direct wphotoproduction process is studied within a formalism based on a chiral constituent quark model approach, complemented with a one-gluon-exchange mechanism, to take into account the breakdown of the SU（6）0（3） symmetry. In the models search, the following known nucleon resonances are embodied： Sll （1535）, $11（1650）, Pll （1440）, Pl1（1710）, P13（1720）, D13（1520）, D13（1700）, D15（1675）, and F15（1680）. Data for the π-p →ηnreaction from threshold up to a total center-of-mass energy of W ≈ 2 GeV are satisfactorily reproduced. For the photoproduction channel, two additional higher mass known resonances, P13 （1900） and F15 （2000）, are also considered. However, reproducing the data for γ＇p →ηP requires, within our approach, two new nucleon resonances, for which we extract mass and width.

Production of hidden-charm and hidden-bottom pentaquark states in electron-proton collisions

Electro-production of several pentaquark states is investigated in this study.The eSTARlight package is adapted to study the electro-production of J/ψand γ(1S)via pentaquark P_(c)and P_(b)resonance channels in ep→eJ/ψp and ep→eγ(1S)p scattering processes at the proposed electron-ion colliders(EICs).The results obtained in this study are compared to those of non-resonance t-channels,which are described in the pomeron exchange model developed in our studies.Some pseudo-rapidity and rapidity distributions of J/ψand γ(1S)are presented for the proposed EICs,including EicC and EIC-US.It is found that EicC is a good platform to identify P_(b) states in the future.

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.

Hadro- and photo-production of η′ in quasi-free proton and neutron processes

The η′ photoproduction process on quasi-free proton and neutron and the reaction NN→ η′NN are investigated within a relativistic effective Lagrangian approach to hadronic interactions. Resonances with spins 1/2 and 3/2 are considered together with the nucleonic and t-channel meson-exchange current contributions. In photoproduction processes, the S11 resonance is found to be responsible for the sharp rise of the cross sections near threshold. In pp → η′pp, it is found that the S11 resonance dominates the total cross section over the entire energy region considered. The spin observables, in particular the beam and target asymmetries, are shown to be very sensitive to the reaction mechanism and will help impose more stringent constraints on the model parameters.

Hunting η-bound nuclei

The η meson can be bound to atomic nuclei.Experimental search is discussed in the form of final state interaction for the reactions dp → 3 Heη and dd → 4 Heη.For the latter case tensor polarized deuterons were used in order to extract the s-wave strength.For both reactions complex scattering lengths are deduced： a 3 Heη = ± 10.7±0.8 ＋0.1 -0.5 ＋i· 1.5±2.6 ＋1.0-0.9 fm and a 4 Heη = [±（3.1±0.5）＋i·（0±0.5）] fm.In a two-nucleon transfer reaction under quasi-free conditions,p^ 27 Al → ^3 HeX,was investigated.The system X can be the bound 25 Mg η at rest.When a possible decay of an intermediate N （1535） is required,a highly significant bump shows up in the missing mass spectrum.The data give for a bound state a binding energy of 13.3±1.6 MeV and a width of σ=4.4±1.3 MeV.

N*(1535) contribution in pp→ppη′ and pn→dφ

In an effective Lagrangian model we find that the N＊（1535） resonance contribution might be important to the interpretation of the present data of the pp →ppη＇ and pn →dφ reactions. The strong coupling strength of N＊ （1535） to η＇ and φ are indicated, and the possible implication to the intrinsic component of N＊（1535） is explored. These results may provide hints to the real origin of the OZI rule violation. It is stressed that further measurements could be performed at China. the Cooling Storage Ring （CSR） at Lanzhou of

Study of excited nucleon states at EBAC:status and plans

We present an overview of a research program for the excited nucleon states in Excited Baryon Analysis Center （EBAC） at Jefferson Lab. Current status of our analysis of the meson production reactions based on the unitary dynamical coupled-channels model is summarized, and the N＊ pole positions extracted from the constructed scattering amplitudes are presented. Our plans for future developments are also discussed.