Proton-antiproton annihilation and mason 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 <(p)over bar 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 phi mesons is larger than predicted in several annihilation channels. Important contributions to the spectroscopy of light mesons have been made. The exotic <(rho)over cap>(1405) meson with quantum numbers J(PC) =1(-+) has been observed in its eta pi decay mode. Two 2(-+) isoscalar mesons eta(2)(1645) and eta(2)(1870), and the 0(-+) isoscalar meson eta(1410) have been observed in the eta pi pi decay channel. From three-body annihilations three 0(++) mesons, a(0)(1450), f(0)(1370), and f(0)(1500) have been established in various decay modes. One of them, f(0)(1500), may be identified with the expected ground-state scalar glueball. [S0034-6861(98)00404-8].