Speaker
Mikhail Mikhasenko
(HISKP, Universität Bonn)
Description
Identifying properties of excited hadronic states in the light meson sector remains an ongoing challenge, due to large widths, significant overlaps, and multiple decay channels of the resonances.
A systematic approach using the unitarity-based coupled channel frameworks is required; for the reaction-independent determination of the resonance parameters, the pole positions of the resonances need to be extracted.
As will be shown in the talk, several works in this direction have been performed by the Joint Physics Analysis Center (JPAC) in the past year in the tensor ($J^{PC}=2^{++}$) and exotic ($J^{PC}=1^{-+}$) waves of $\eta(')\pi$ system measured by the COMPASS experiment ([PLB 779 (2018)](http://inspirehep.net/record/1609260) and
[arXiv:1810.04171](http://inspirehep.net/record/1697661)).
The spin-exotic sector $J^{PC}=1^{-+}$ is also accessible from the partial wave analysis of the three pions system measured in diffractive reaction $\pi\,p \to 3\pi\,p$, however, the studies are hampered by the presence of a large, coherent, non-resonant background, known as the Deck process. I will highlight ongoing work on a comparison of the various models for this non-resonant production and show its influence found in the data. As the first steps in the route of understanding interaction in the $J^{PC}=1^{++}$ sector and the Deck process, we have built a model based on the approximate three-body unitary, fixed the free parameters by fitting it to the clean ALEPH data on $\tau\to 3\pi\,\nu_\tau$ decay. The pole position of the $a_1(1260)$ has been extracted for the first time using the unitary model ([PRD 98 (2018), 096021](http://inspirehep.net/record/1696497)).
Primary author
Mikhail Mikhasenko
(HISKP, Universität Bonn)
