  In order to study diffractive dissociation reactions, COMPASS has taken data
with a 190 GeV/$c$ pion beam impinging on a liquid hydrogen target in 2008 and
2009. At squared four-momentum transfers to the target t' between 0.1
GeV$^2/c^2$ and 1.0 GeV$^2/c^2$ the number of events with three pions in the
final state is about an order of magnitude larger than that acquired by any
previous experiment. In COMPASS, the three-pion final state can be studied in
the two channels $\pi^-\pi^-\pi^+$ and $\pi^-\pi^0\pi^0$. The large data sample
in particular for the $\pi^-\pi^-\pi^+$ channel allows to find even small
signals at the sub-percent level. The progress of the partial-wave analysis
will be shown. Compared to previous COMPASS results, the analysis is now
performed in bins of t', and the set of partial waves has been extended now
including waves up to spin 6. The information from the t' dependence of the
individual partial waves is very helpful in separating resonant and
non-resonant contributions. As a consistency check results from the
$\pi^-\pi^-\pi^+$ channel will be compared to the $\pi^-\pi^0\pi^0$ channel.

High Energy Physics - Experiment;Nuclear Experiment