Speaker
Description
The COMPASS experiment has collected a very large data set of 50 million
diffractively produced $\pi^-\pi^+\pi^-$ events using a $190\,$GeV$/c$
negatively charged hadron beam. In addition to the results of an
extensive Partial-Wave Analysis (PWA) of this data, we recently
published first results of a so-called freed-isobar PWA. In this
approach, fixed parametrizations of intermediate $\pi^+\pi^-$ resonances
are replaced by piecewise constant functions, which leads to a less
biased extraction of two- and three-particle amplitudes. The success of
this first analysis, which was limited to 3 partial waves with $J^{PC} =
0^{++}$ of the two-pion subsystem, led to an extension of the method to
include also waves with $J^{PC} = 1^{--}$ and $2^{++} two-pion
subsystems. First results from Monte Carlo studies will be presented. We
will also discuss the ambiguities that arise in these extended
free-isobar PWAs and will show how to resolve them.
