Evidence of new nucleon resonances from electromagnetic meson production

TL;DR

This paper discusses how electromagnetic meson production experiments, especially with the CLAS detector, reveal new nucleon resonances that are difficult to detect via traditional pion scattering methods.

Contribution

It presents evidence of previously unobserved nucleon resonances through advanced electromagnetic meson production techniques using polarized beams and targets.

Findings

Identification of new nucleon resonance states

Enhanced understanding of the nucleon excitation spectrum

Impact of high-statistics data on resonance clarification

Abstract

The study of nucleon resonances in electromagnetic meson production with the CLAS detector is discussed. The electromagnetic interaction is complementary to pion scattering in the exploration of the nucleon excitation spectrum. Higher mass states often decouple from the $N\pi$ channel and are not seen in $\pi N \to \pi N$. Photoproduction of mesons, such as $K\Lambda$, $\omega p$ and $\eta^\prime p$ may be more sensitive to many of these states. The CLAS detector, combined with the use of energy-tagged polarized photons and polarized electrons, as well as polarized targets and the measurement of recoil polarization, are the tools needed for a comprehensive nucleon resonance program. Some of the recently published high statistics data sets had significant impact on further clarifying the nucleon excitation spectrum.