Resonant π₂ poles from 3 π data.

Mar 16, 2017, 5:30 PM
Lecture Hall (Bad Honnef)

Lecture Hall

Bad Honnef

Topic 1: Spectroscopy of Baryons, Light- and Heavy-Quark Mesons Session


Mr Mikhail Mikhasenko (University of Bonn (DE))


High-energy peripheral reactions provide an excellent opportunity to study the excitation spectrum of hadrons. The COMPASS experiment at CERN has collected $5\times10^6$ events of the diffractive scattering of pions to the 3-pion final state.
Partial wave analysis techniques have been employed to obtain an expansion of the
reaction cross section in terms of partial waves with quantum numbers $J^{PC}\,M^\varepsilon$.
Since around hundred of observed resonances in light sector are coupled to pionic systems
the spin-density matrices from COMPASS PWA are extremely valuable data to identify ordinary and, possibly, exotic mesons.

The aim of our analysis is to extract three pion scattering amplitudes
from mass-dependence of the COMPASS spin-density matrices using analyticity and unitarity constraints.

Three-body unitarity problem is very difficult and has not been completely solved.
Our approximation of those constraints is reduced in the isobar model by quasi-two-body
($\pi\pi$-subchannnel resonance + pion) unitarity requirements.
K-matrix approach is used to parametrize scattering matrix.
We invoke an unitarization procedure to incorporate
non-resonant long-range production processes via pion exchange, i.e. ``Deck''-like processes.

The developed theoretical framework is applied to the COMPASS data.
We discuss resonant pole positions of $\pi_2$ mesons located at the unphysical sheet, spurious poles caused by the parametrization and stability of solutions with respect to the changes in the model.

Primary author

Mr Mikhail Mikhasenko (University of Bonn (DE))


Andrew Jackura (Indiana University) Bernhard Ketzer (University of Bonn (DE)) Adam Szczepaniak (iu)

Presentation materials