Meson Spectroscopy at COMPASS

QCD predicts four quark states or gluonic excitations like hybrids or glueballs to contribute to the meson spectrum in addition to $q\overline{q}$ pair configurations. The most promising way to identify such states is the search for $J^{PC}$ quantum number combinations which are forbidden in the constituent quark model. The fixed target COMPASS experiment at CERN offers the opportunity to search for such states in the light quark sector with an unprecedented statistics. Diffractive reactions of 190 GeV/c pions on a lead target were studied by COMPASS during a pilot run in 2004. A Partial Wave Analysis (PWA) of the $\pi^{−}\pi^{−}\pi^{+}$ final state with 42 waves including acceptance corrections through a phase-space Monte Carlo simulation of the spectrometer was performed. The exotic $\pi_{1}$(1600) meson with quantum numbers $J^{PC}= 1^{−+}$ has been clearly established in the rho-pi decay channel with a mass of 1660 $\pm$ 10(stat) MeV/c$^{2}$ and a width of 269 $\pm$ 21(stat) MeV/c$^{2}$. The final state with 5 charged pions was also investigated. The improved detector performance in 2008 allows us to study many further diffractively and centrally produced resonances with neutral as well as charged particles in the final state. First results of the ongoing analysis of the 2008 data taking period, using a 190 GeV/c pion beam on a liquid hydrogen target are presented in this paper.