Vector meson electroproduction in QCD

Based on the generalized QCD vector meson dominance model, we study the electroproduction of a vector meson off a proton in the QCD inspired eikonalized model. Numerical calculations for the total cross section σ tot and differential cross section dσ/dt are performed for ρ, ω and φ meson electroproduction in this paper. Since gluons interact among themselves （self-interaction）, two gluons can form a glueball with quantum numbers I G , J P C = 0 ＋ , 2 ＋＋ , decay width Γ t ≈ 100 MeV, and mass of m G =2.23 GeV. The three gluons can form a three-gluon colorless bound state with charge conjugation quantum number C = 1, called the Odderon. The mediators of interactions between projectiles （the quark and antiquark pair fluctuated from the virtual photon） and the proton target （a three-quark system） are the tensor glueball and the Odderon. Our calculated results in the tensor glueball and Odderon exchange model fit to the existing data successfully, which evidently shows that our present QCD mechanism is a good description of meson electroproduction off a proton. It should be emphasized that our mechanism is different from the theoretical framework of Block et al. We also believe that the present study and its success are important for the investigation of other vector meson electro- and photoproduction at high energies, as well as for searching for new particles such as tensor glueballs and Odderons, which have been predicted by QCD and the color glass condensate model （CGC）. Therefore, in return, it can test the validity of QCD and the CGC model.

Single photo and electroproduction of pions at EBAC@JLAB

Within the Excited Baryon Analysis Center we have performed a dynamical coupled-channels analysis of the available p（e,e＇π）N data in the region of W ≤ 1.6 GeV and Q2 ≤1.45 （GeV/c）2. The channels included are γ＊N, π＊N, ηN, and ηN which has π△, pN, and σN components. With the hadronic parameters of the model determined in our previous investigations of πN→ πN reaction, we have found that the available data in the considered W ≤ 1.6 GeV region can be fitted well by only adjusting the bare γ＊N → N＊ helicity amplitudes for the lowest N＊ states in P33, P11, S11 and D13 partial waves. The meson cloud effect, as required by the unitarity conditions, on the γ＊N → N＊ form factors are examined.

Identifying hidden charm pentaquark signal from non-resonant background in electron–proton scattering

In this study,we analyze the electroproduction of the LHCb pentaquark states with the assumption that they are resonant states.Our main concern is to investigate the final state distribution in the phase space to extract a feeble pentaquark signal from a large non-resonant background.The results indicate that the signal to background ratio will increase significantly with a proper kinematic cut,which will be beneficial for future experimental analysis.

Baryon resonance analysis from MAID

The unitary isobar model MAID2007 has been used to analyze the recent data of pion electroproduction. The model contains all four-star resonances in the region below W = 2 GeV and both single-Q2 and Q2 dependent transition form factors could be obtained for the Delta, Roper, D13（1520）, S11 （1535）, S31 （1620）, $11（1650）, D15（1675）, F15（1680） and P13（1720）. From the complete world data base, including also π data on the neutron, also Q2 dependent neutron form factors are obtained. For all transition form factors we also give convenient numerical parameterizations that can be used in other reactions. Furthermore, we show how the transition form factors can be used to obtain empirical transverse charge densities and our first results are given for the Roper, the S11 and D13 resonances.