2022/02/26 by Cao, Xiong-Hui, Ma, Yao
#FOS: Physical sciences #High Energy Physics - Phenomenology (hep-ph)
paper · doi:10.48550/arxiv.2202.13082
A dispersive representation based on unitarity and analyticity is used to study the low energy γN → πN and γ^* N → πN partial wave amplitudes. Final state interactions of the πN system are critical to this analysis. The left-hand cut contribution is estimated by invoking baryon chiral perturbation theory results, while the right-hand cut contribution responsible for final state interaction effects is taken into account via an Omnès 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 E0+, S0+ in the energy region below the Δ(1232) are well described when the photon virtuality Q2 ≤ 0.1 GeV2. Furthermore, we extend the partial wave amplitudes to the second Riemann sheet to extract the couplings of the subthreshold resonance N^*(890). Its couplings extracted from the multipole amplitudes E0+, S0+ are comparable to those of the N^* (1535) resonance.