Bonn 2020 – wissenschaftliches Programm

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HK: Fachverband Physik der Hadronen und Kerne

HK 13: Hadron Structure and Spectroscopy III

HK 13.4: Vortrag

Dienstag, 31. März 2020, 18:00–18:15, J-HS A

Final fit of the a1(1420) as a triangle singularity — •Mathias Wagner1, Mikhail Mikhasenko2, and Bernhard Ketzer1 for the COMPASS collaboration — 1Universität Bonn, Helmholtz-Institut für Strahlen- und Kernphysik, 53115 Bonn, Germany — 2CERN, Geneva, Switzerland

In the recent past several new particle candidates (e.g. the X,Y,Z states in the charmed sector) were found which do not fit into the simple constituent-quark models for mesons and baryons. Different concepts were introduced in order to find an explanation for these exotic states. One of them is a rescattering effect in the three-particle system. Here, triangle diagrams can produce resonance-like signals.

One prominent example is the a1(1420) signal, observed by the COMPASS experiment in the JPC=1++ partial wave decaying to f0(980)π in a P-wave.

By coupling the KKπ and the 3π final states we obtain a first order approximation to the Khuri-Treiman equation for the 1++ sector. We present the fit results of the finalized model, where we properly include all involved spins via a dispersion integral over a partial wave projection of the KKπ final state onto the 3π final state, using a general π K P-wave amplitude.

Many systematic studies were performed, including a bootstrap analysis and an investigation of other contributions to the decay amplitude. A comparison to a fit with a genuine-resonance model is done for all cases.

Supported by BMBF.

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