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Zhenping Li

Publications and source records attributed to Zhenping Li.

27 records · Page 2Linked to original sources
arXiv1995

The eta Photoproduction of Nucleons and The structure of the Resonance S11(1535) in The Quark Model

In this paper, we present our study on the $η$ photoproduction based on the chiral quark model. We find that quark model provides a very good description of the $η$ production with much less parameters, and the threshold region is not a reliable source to determine the $ηNN$ coupling constant due to its strong dependence on the properties of the resonance $S_{11}(1535)$. We suggest that the systematic data in $E_{lab}=1.2 \sim 1.4$ GeV region may help us to determine the $ηNN$ coupling constant more precisely. The structure of the resonance $S_{11}(1535)$ is discussed, we find that the recent data from Mainz group bring the helicity amplitude much closer to the quark model prediction. However, more studies need to be done to understand the large $ηN$ branching ratio of the resonance $S_{11}(1535)$. Our results show that the quark model is a very good approach to study the underlying structure of baryon resonances from the meson photoproduction data.

nucl-th↗
arXiv1995

The Kaon-Photoproduction Of Nucleons In The Quark Model

In this paper, we develop a general framework to study the meson-photoproductions of nucleons in the chiral quark model. The S and U channel resonance contributions are expressed in terms of the Chew-Goldberger-Low-Nambu (CGLN) amplitudes. The kaon-photoproduction processes, $γp\to K^+ Λ$, $γp\to K^+ Σ^0$, and $γp\to K^0Σ^+$, are calculated. The initial results show that the quark model provides a much improved description of the reaction mechanism for the kaon-photoproductions of the nucleon with less parameters than the traditional phenomenological approaches.

hep-ph↗
arXiv1994

The Isospin Splittings of Heavy-Light Quark Systems

The isospin mass splittings of the pseudoscalar and vector D and B light-heavy quark system have been calculated using the method of QCD sum rules. Nonperturbative QCD effects are shown to be very small, so that mass splittings arise almost completely from current quark mass splitting and electromagnetic effects, for which a new gauge invariant QED treatment is used. The results are consistent with experiment. A measurement of the isospin splitting of the vector B mesons would give valuable information about quark mass splittings.

hep-ph↗
arXiv1994

Longitudinal Transitions Of Baryon Resonances in Constituent Quark Model

A longitudinal transition operator that satisfies the gauge invariance requirement is introduced in constituent quark model. The corresponding longitudinal transitions between the nucleon and baryon resonances are calculated. We show that the study of the longitudinal coupling plays an important role in understanding the structure of baryons.

hep-ph↗
arXiv1994

The Threshold Pion-Photoproduction of Nucleons In The Chiral Quark Model

In this paper, we show that the low energy theorem (LET) of the threshold pion-photoproduction can be fully recovered in the quark model. An essential result of this investigation is that the quark-pion operators are obtained from the effective chiral Lagrangian, and the low energy theorem does not require the constraints on the internal structures of the nucleon. The pseudoscalar quark-pion coupling generates an additional term at order $μ=m_π/M$ only in the isospin amplitude $A^{(-)}$. The role of the transitions between the nucleon and the resonance $P_{33}(1232)$ and P-wave baryons are also discussed, we find that the leading contributions to the isospin amplitudes at $O(μ^2)$ are from the transition between the P-wave baryons and the nucleon and the charge radius of the nucleon. The leading contribution from the P-wave baryons only affects the neutral pion production, and improve the agreement with data significantly. The transition between the resonance $P_{33}(1232)$ and the nucleon only gives an order $μ^3$ corrections to $A^{(-)}$.

hep-ph↗
arXiv1994

The Isospin Splittings of Heavy-Light Quark Systems

The mass splittings of the pseudoscalar and vector D and B light-heavy quark systems have been calculated using the method of QCD sum rules. Electromagnetic, quark mass, and nonperturbative QCD effects are all included. The results are in good agreement with experiment. A measurement of isospin splitting for the vector B mesons would give valuable information about quark mass splittings.

hep-ph↗
arXiv1994

On The $Q^2$ Dependence of The Spin Structure Function In The Resonance Region

In this paper, we show what we can learn from the CEBAF experiments on spin-structure functions, and the transition from the Drell-Hearn-Gerasimov sum rule in the real photon limit to the spin dependent sum rules in the deep inelastic scattering, and how the asymmetry $A_1(x,Q^2)$ approaches the scaling limit in the resonance region. The spin structure function in the resonance region alone can not determine the spin-dependent sum rule due to the kinematic restriction of the resonance region. The integral $\int_0^1 \frac {A_1(x,Q^2)F_2(x,Q^2)}{2x(1+R(x,Q^2))}dx$ is estimated from $Q^2=0$ to $2.5$ GeV$^2$. The result shows that there is a region where both contributions from the baryon resonances and the deep inelastic scattering are important, thus provides important information on the high twist effects on the spin dependent sum rule.

hep-ph↗
arXiv1992

Effective Heavy Quark Theory

We show how heavy quark effective theory, including 1/M corrections, may be matched onto dynamical quark models by making a specific choice of K,m and v in the p=mv+K expansion. We note that Wigner rotations of heavy quark spins arise at $O(p^2/m^2)$ in non-relativistic models but at $O(Λ_{QCD}/M_Q)$ or O(velocity-transfer) in HQET and so are necessary for a consistent treatment.

hep-ph↗