MESON PRODUCTION FROM DIFFRACTIVE PION DISSOCIATION AT COMPASS

Diffractive dissociation reactions at COMPASS provide clean access to mesons with masses below ≈ 2.5 GeV/c². This paper presents a partial wave analysis of about 420 000 π^-Pb → π^-π^-π⁺Pb events at 190 GeV/c beam momentum and with four-momentum transfer t' ∈ [0.1,1] GeV²/c². The well-known a₁(1260), a₂(1320) and π₂(1670) mesons are resolved with high quality. Also the less established states π(1800) and a₄(2040) are seen. In addition, a resonance in the spin-exotic J^PC = 1^-+ wave is observed. A mass-dependent fit results in a mass and width of and , respectively, which is consistent with the disputed hybrid candidate π₁(1600).