Diffractive Dissociation into $\pi^{-}\pi^{-}\pi^{+}$ Final States at COMPASS

Diffractive dissociation reactions studied at the COMPASS experiment at CERN provide access to the light-meson spectrum. During a pilot run in 2004, using a pion beam and a lead target, 420k $\pi^{-}\pi^{-}\pi^{+}$ final-state events with masses below 2.5 GeV/c$^{2}$ were recorded, yielding a significant spin-exotic signal for the controversial $\pi_{1}$(1600) resonance. After a significant upgrade of the spectrometer in 2007, the following two years were dedicated to meson spectroscopy. Using again a pion beam, but now with a liquid hydrogen target, an unique statistics of ~100M events of the same final state was gathered in 2008. During a short campaign in 2009, the H$_{2}$ target was exchanged by several solid state targets in order to compare final states produced on targets with different atomic numbers. A partial-wave Analysis (PWA) was performed on all these data sets and results are presented.