Proton-antiproton annihilation and meson spectroscopy with the Crystal Barrel

This report reviews the achievements of the Crystal Barrel experiment at the Low-Energy Antiproton Ring (LEAR) at CERN. During seven years of operation Crystal Barrel has collected very large statistical samples in p̄p annihilation, especially at rest and with emphasis on final states with high neutral multiplicity. The measured rates for annihilation into various two-body channels and for electromagnetic processes have been used to test simple models for the annihilation mechanism based on the internal quark structure of hadrons. The production of φ mesons is larger than predicted in several annihilation channels. Important contributions to the spectroscopy of light mesons have been made. The exotic ρ ̂ \^(1405) meson with quantum numbers JPC=1^-+ has been observed in its ηπ decay mode. Two 2^-+ isoscalar mesons η₂(1645) and η₂(1870), and the 0^-+ isoscalar meson η(1410) have been observed in the ηππ decay channel. From three-body annihilations three 0⁺⁺ mesons, a₀(1450), f₀(1370), and f₀(1500) have been established in various decay modes. One of them, f₀(1500), may be identified with the expected ground-state scalar glueball.