Four Sorts of Mesons

TL;DR

This paper reviews the spectrum of light non-strange mesons up to 2400 MeV, discussing established states, glueball and hybrid candidates, and anomalously light mesons based on extensive experimental data.

Contribution

It provides a comprehensive classification and review of meson states, including new insights into glueball, hybrid, and light meson candidates from recent experimental results.

Findings

Complete and secure spectrum for I=0, C=+1 mesons.

Identification of glueball candidates fo(1500), fo(2100), f_2(1950), eta(2190).

Recognition of anomalously light mesons sigma(540), kappa(750), a_0(980), f_0(980).

Abstract

This report reviews the extensive spectrum of light non-strange qbar-q states up to a mass of 2400 MeV from Crystal Barrel and PS172 data on pbar-p -> Resonance -> A + B in 17 final states. For I=0, C=+1, the spectrum is complete and very secure. Glueball candidates fo(1500), fo(2100), f_2(1950) and eta(2190) are reviewed and also hybrid candidates eta_2(1870) and pi_2(1880). A fourth category of anomalously light 0+ mesons is made of sigma(540), kappa(750), a_0(980) and f_0(980).