Speaker
Description
One of the goals of the COMPASS experiment is the precision study of light meson
spectroscopy, with data for various final states collected in two years of data
taking. With $46\cdot10^6$ exclusive events, the process
$\pi^-p\to\pi^-\pi^+\pi^-p$ constitutes the flagship of these channels.
Based on this data set, an extensive Partial Wave Analysis, using a total of 88
partial waves in the model, was published in 2017 [1]. Along with it,
results of a first study of the so-called freed-isobar method were shown. Here,
the fixed amplitudes for appearing $\pi^+\pi^-$ intermediate states used in the
conventional analysis were replaced by sets of piecewise constant functions to
extract the amplitudes of the $\pi^+\pi^-$ subsystems directly from the data. In
this first study, this was done for three $J^{PC} = 0^{++}$ intermediate
$\pi^+\pi^-$ states.
The promising results inspired further extension of this method, by also
including intermediate $\pi^+\pi^-$ states with $J^{PC} = 1^{--}$ and $2^{++}$.
With this extension of the sets of freed waves, mathematical ambiguities in the
model arise due to the much higher freedom in the model. We will present first
results of these extended studies on COMPASS data along with methods to overcome
the arising ambiguities.
[1] COMPASS collaboration, Phys.Rev. D95 (2017) no.3, 032004
