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 p̅ p 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 ρ̂(1405) meson with quantum numbers J^PC=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.