Photo- and Electron-Production of Mesons on Nucleons and Nuclei

TL;DR

This paper discusses the application of the chiral unitary approach to meson photo- and electroproduction on nucleons and nuclei, revealing insights into resonance behaviors, mesonic states, and medium modifications of mesons.

Contribution

It applies the chiral unitary approach to various meson production processes, providing new interpretations of resonance structures and meson properties in nuclear media.

Findings

Reproduction of experimental data for $ ext{e}^+ ext{e}^- o ext{phi} f_0(980)$ with indications of a new resonance X(2175)

Demonstration that $ ext{N}^*(1535)$ is dynamically generated in the approach

Evidence for significant in-medium broadening of the $ extomega$ meson

Abstract

In these lectures I will show some results obtained with the chiral unitary approach applied to the photo and electroproduction of mesons. The results for photoproduction of $\eta \pi^0 p$ and $K^0 \pi^0 \Sigma^+$, together with related reactions will be shown, having with common denominator the excitation of the $\Delta(1700)$ resonance which is one of those dynamically generated in the chiral unitary approach. Then I will show results obtained for the $e^+ e^- \to \phi f_0(980)$ reaction which reproduce the bulk of the data except for a pronounced peak, giving support to a new mesonic resonance, X(2175). Results will also be shown for the electromagnetic form factors of the $N^*(1535)$ resonance, also dynamically generated in this approach. Finally, I will show some results on the photoproduction of the $\omega$ in nuclei, showing that present experimental results claiming a shift of the $\omega$ mass in the medium are tied to a particular choice of background and are not conclusive. One the other hand, the same experimental results show unambiguously a huge increase of the $\omega$ width in the nuclear medium.