Mainz-Tuzla-Zagreb PWA

Mainz - Tuzla - Zagreb Partial Wave Analysis is collaboration of physicists from Johannes Gutenberg-Universität Mainz, Univesity of Tuzla and Institute Ruđer Bošković Zagreb. The main focus of this collaboration is a unique extraction of partial wave amplitudes and resonance parameters from the available data without assuming any explicit reaction model. This will be achieved by taking into account the fixed-t analytic properties of the underlying amplitudes. The method originates from the Karlsruhe-Helsinki PWA of πN scattering where an efficient method for imposing constraints from fixed-t analyticity was developed and applied. Our goal is to adapt this strategy to photoproduction and to implement it in single-energy partial wave analyses.

We are following a 3-fold strategy:

  • Development of new MAID isobar models. The models include explicit resonances on top of a non-resonant background, which consists of Born-terms and t-channel Regge exchanges.
  • Isobar models violate fixed-t dispersion relations, which can be derived from analyticity and crossing symmetry.  We work on modifications of our models in order to fulfill fixed-t dispersion relations.
  • The least biased determination of multipole amplitudes is possible in so called single- energy or energy-independent analyses. Here, a truncated partial wave expansion of the measured angular distributions is performed at each individual energy bin without assuming any model for the energy-dependence. However, it can be shown that fully unconstrained single-energy analyses lead to ambiguities which cannot be resolved by experimental data alone. In order to avoid model constraints we have developed and applied a new method using fixed-t analyticity in an iterative fitting procedure at fixed-t and fixed energy.