SMuK 2021 – scientific programme
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HK: Fachverband Physik der Hadronen und Kerne
HK 29: Hadron Structure and Spectroscopy VI
HK 29.7: Talk
Friday, September 3, 2021, 15:45–16:00, H3
Fit of the a1(1420) as a triangle singularity — •Mathias Wagner and Bernhard Ketzer — HISKP, Uni Bonn, Germany
In the recent past several new particle candidates 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. Here, triangle diagrams can produce resonance-like signals, both in the intensity and the relative phase of the corresponding partial wave.
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.
We present the fit results of the finalized model, where we properly include all involved spins via a dispersive integral over a partial wave projection of the KKπ final state onto the 3π final state. It shows that the a1(1420) can be fully explained by the decay of the ground-state a1(1260) into K*K and subsequent rescattering through a triangle singularity into the observed final state f0(980)π without the need of a new genuine a1 resonance. The effect of the triangle singularity, which is expected to be present, is sufficient to explain the observation. (accepted PRL)