Speaker
Xiong-Hui Cao
(Peking University)
Description
A dispersive representation based on unitarity and analyticity is used to study the low energy $\gamma N \rightarrow \pi N$ and $\gamma^{*} N \rightarrow \pi N$ partial wave amplitudes.
Final state interactions of the $\pi N$ system are critical to this analysis.
The left-hand cut contribution is estimated by invoking $\mathcal{O}(p^{2})$ baryon chiral perturbation theory results,
while the right-hand cut contribution responsible for final state interaction effects is taken into account via an Omnes formalism with elastic phase shifts as input.
It is found that a good numerical fit can be achieved with only one subtraction parameter, and the experimental data of the multipole amplitudes $E_{0}^{+}, S_{0}^{+}$ in the energy region below the $\Delta(1232)$ are well described when the photon virtuality $Q^{2} \leq 0.1 \text{GeV}^{2}$.
Furthermore, we extend the partial wave amplitudes to the second Riemann sheet to extract the couplings of the subthreshold resonance $N^{*}(890)$.
The values of residue of the multipole amplitudes $E_{0}^{+}, S_{0}^{+}$ are almost the same as that of the $N^{*}(1535)$ resonance, indicating that $N^{*}(890)$ strongly couples to the $\pi N$ system.
Primary author
Xiong-Hui Cao
(Peking University)
Co-authors
Prof.
Han-Qing Zheng
(Sichuan University)
Yao Ma
(Hangzhou Institute for Advanced Study)
