25-29 September 2017
Salamanca, Spain
Europe/Zurich timezone

## A resonance-like phenomenon $a_1(1420)$

26 Sep 2017, 15:35
20m
Aula 2.3

#### Aula 2.3

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### Speaker

Mikhail Mikhasenko (University of Bonn (DE))

### Description

We investigate the resonance-like structure with quantum numbers $J^{PC} = 1^{++}$ in the $f_{0}\pi$ P-wave recently observed at a mass $1.4\,$GeV by the COMPASS Collaboration. The signal was tentatively assigned to be an axial resonance, $a_{1}(1420)$, although it does not fit the $q\bar{q}$-model, which suggests an exotic nature. We present an elegant explanation of the phenomenon without introducing a new state. We show that in the presence of a significant inelasticity, particularly $3\pi-K\bar{K}\pi$ coupling, strong effects due to rescattering appear, producing a resonance-like enhancement in the three-body invariant mass. The model which does not have free parameters is tested with the COMPASS data, showing that both the peak in the intensity and the phase variation can be reproduced.

We see that the common approach called the isobar model, which assumes that a decay to multiparticle final states is described by sequential two-body decays, requires rescattering corrections. The studies of the generalization of the isobar model guided by subchannel unitarity and three-body unitarity will be discussed.

### Primary author

Mikhail Mikhasenko (University of Bonn (DE))

### Co-authors

Mathias Wagner (HISKP, Univarsität Bonn) Prof. Bernhard Ketzer (University of Bonn (DE)) Andrey Sarantsev (HISKP)