Speaker
Fabian Krinner(M)
Description
Modern hadron-spectroscopy experiments such as COMPASS collect data samples of unprecedented size, so that novel analysis techniques become possible and necessary. One such technique is the freed-isobar partial-wave analysis (PWA). In this approach, fixed parametrizations for the amplitudes of intermediate states–commonly modeled using Breit-Wigner shapes–are replaced by sets of step-like functions that are determined from the data. This approach not only reduces the model dependence of partial-wave analyses, but also allows us to study the amplitudes of the intermediate states and their dependence on the parent system. Since such an approach leads to a dramatic increase in degrees of freedom of the PWA model, continuous mathematical ambiguities may appear in fits to data. We will show, how these ambiguities can be identified and resolved without spoiling the advantage of model-independence. We will also present results of a freed-isobar PWA performed on the large data set on diffractive production of three charged pions collected by the COMPASS experiment, which consists of $46\times10^6$ exclusive events. We will focus on results for the wave with spin-exotic quantum numbers $J^{PC}=1^{-+}$, in particular on its decay into $\rho(770)+\pi^-$. Here, the freed-isobar PWA method provides insight into the interplay of three- and two-particle dynamics.
