Corrections to the Forward Limit Dispersion Relations for γZ\gamma Z-Exchange Contributions

In the past fifteen years, dispersion relations (DRs) in the forward limit have been widely accepted as a model-independent method for estimating the $\gamma Z$-exchange contributions to the parity asymmetry $A_{\textrm{PV}}$ in elastic $ep$ scattering. In this work, for the first time, we estimate the corrections to these DRs. Firstly, we analyze the properties of $A_{\textrm{PV}}$ based on a general formalism, and discuss the possibility of the DRs breaking down due to two kinematic poles in $A_{\textrm{PV}}$. Then, we use point-like interactions as an example to illustrate the exact breakdown of these DRs at the experimental energy regions. Furthermore, by using the effective low-energy interactions, we estimate the $\gamma Z$-exchange contributions for the upcoming P2 experiment, and the results indicate that the correction to the forward limit DR for $\Box_{\gamma Z}^{V}$ is abot 47\%, which is significantly larger than the naive expectation prior to this study.Comment: 4 figure

Two-Photon-Exchange effect in ep→enπ+ep\rightarrow en\pi^+ at small −t-t with the hadronic model and dispersion relation approach

In this work, the two-photon-exchange (TPE) effect in $ep\rightarrow en\pi^+$ at small $-t$ is discussed. In the previous work, the TPE contribution with one $\pi$ intermediate state is estimated numerically within a hadronic model under the pion-dominance approximation. Here we extend the discussion to include one $\rho$ intermediate state. The TPE contribution can be described by one scalar function in the limit $m_e\rightarrow 0$, the dispersion relation (DR) satisfied by this scalar function is analysed. The analytic expressions for the imaginary parts of the TPE contributions from one $\pi$ or one $\rho$ intermediate state are given within the hadronic model. Combining these analytic expressions and the DR, the corresponding real parts of the TPE contributions can be estimated easily at any available region. This can help the further experimental analysis to include the TPE contributions in a convenient way. The numeric results show that the TPE correction with one $\rho$ intermediate state is much smaller than that with one $\pi$ intermediate state in the current energy region. These results suggest that the TPE contribution with an elastic state is the main TPE contribution in $ep\rightarrow en\pi^+$ at small $-t$

Total Nuclear Reaction Cross Section Induced by Halo Nuclei and Stable Nuclei

We develop the method for the calculation of the total reaction cross sections induced by the halo nuclei and stable nuclei. This approach is based on the Glauber theory, which is valid for nuclear reactions at high energy. It is extended for nuclear reactions at low energy and intermediate energy by including both the quantum correction and Coulomb correction under the assumption of the effective nuclear density distribution. The calculated results of the total reaction cross section induced by stable nuclei agree well with the 30 experimental data within 10 percent accuracy.The comparison between the numerical results and the 20 experimental data for the total nuclear reaction cross section induced by the neutron halo nuclei and the proton halo nuclei indicates a satisfactory agreement after considering the halo structure of these nuclei, which implies the quite different mean fields for the nuclear reactions induced by halo nuclei and stable nuclei. The halo nucleon distributions and the root mean square radii of these nuclei can be extracted from above comparison based on the improved Glauber model, which indicate clearly the halo structures of these nuclei. Especially, it is clear to see that the medium correction of the nucleon-nucleon collision has little effect on the total reaction cross sections induced by the halo nuclei due to the very weak binding and the very extended density distribution.Comment: 15 pages,2 figures. Communucations in Theoretical Physics, (2003) in pres