München 2019 – wissenschaftliches Programm
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HK: Fachverband Physik der Hadronen und Kerne
HK 57: Hadron Structure and Spectroscopy VIII
HK 57.5: Vortrag
Freitag, 22. März 2019, 15:15–15:30, HS 13
Incorporating Spin into Rescattering Effects via Partial Wave Projections - The a1(1420) — •Mathias Wagner, Mikhail Mikhasenko, and Bernhard Ketzer for the COMPASS collaboration — Universität Bonn, Helmholtz-Institut für Strahlen- und Kernphysik, 53115 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.
For example, the a1(1420) signal observed by the COMPASS experiment, in the JPC=1++ partial wave decaying to f0(980)π, can be well described with a simplified K*K→ f0π rescattering model neglecting the spin of the intermediate K*. Including the spin of intermediate particles will modify the amplitude.
Exploiting the isobar model we can describe the rescattering as a dispersive integral over a partial wave projection of the KKπ final state onto the 3π final state, using a general π K P-wave amplitude instead of the Breit-Wigner parametrization for K*. This method allows us to include the spin of the K* appearing as an intermediate Kπ-resonance via Wigner-D-matrices, using rotational properties of the helicity amplitudes. Our approach built from analyticity and Lorentz-invariance is considered as an alternative to the method of Feynman diagrams, which is based on an effective Lagrangian. Supported by BMBF.