We present first results of a partial wave analysis of the diffractive
reaction π−Pb→π−π+π−Pb based on data from the COMPASS
experiment taken during a pilot run in 2004 using a 190 GeV/c π− beam on a
lead target. The analysis was performed in the region of squared four-momentum
transfer t′ between 0.1 and 1.0 (GeV/c)^2. The π−π+π− final state
shows a rich spectrum of well-known resonances. In addition a spin-exotic
JPC=1−+ state with significant intensity was observed at 1.66 GeV/c^2
in the ρ(770)π decay channel in natural parity exchange. The resonant
nature of this state is manifest in the mass dependence of its phase difference
to JPC=1++ and 2−+ waves. The measured resonance parameters are
consistent with the disputed π1(1600). An outlook on the analyses of the
much larger data set taken during 2008 and 2009 is given.Comment: 10 pages, 18 figures, proceedings of "19th International IUPAP
Conference on Few-Body Problems in Physics" (FB19), Bonn, Germany, Aug. 31 -
Sept. 5, 200