S3: Light hadron spectroscopy

Research areas

  • Experimental hadron physics
  • Theoretical hadron physics
  • Lattice gauge theory

Principal investigators

Goals

The excitation spectra of hadrons reflect the underlying strong dynamics complementary to polarizabilities, elastic form factors and parton distributions. In this project we will focus on the following topics:

  • Meson photoproduction
    Recently, new high precision cross section and polarization data in meson photoproduction have become the broadest source of information about excited baryons. Several groups try to describe these new data with reaction models and try to understand the resonance contributions. We will contribute to these efforts by providing preliminary MAMI data and by refining the MAID model. However, the main focus is a unique extraction of partial wave amplitudes without assuming any reaction model. Significant data sets for this analysis will be obtained in a combined effort at MAMI and ELSA using the Mainz polarized target at both accelerators in the most efficient way.
  • Baryon resonances in J/ψ decays
    High statistics BESIII data on the decays J/ψ → pp pπ0/pp pη and J/ψ(ψ') → pnπ+/pnπ- will allow us to independently confirm resonance properties determined from photoproduction data. This is an important task especially in the case of new high mass states as well as in case of the Roper-resonance, whose dynamical origin is still intensely discussed. We plan to reconstruct these decays using the full available statistics of the J/ψ and ψ' datasets from BESIII and to perform an amplitude analysis for the interpretation.
  • Light flavour resonances in lattice QCD
    Lattice QCD calculations of hadronic scattering phases will be carried out based on Lüscher's method. The first calculations are planned in the mesonic sector. As a first application of the methods developed under S3, the ρ channel will be investigated as part of project P1, where also the timelike pion form factor will be computed. This will serve as a benchmark for further calculations under S3. The latter will include an investigation of the a0 meson in the two-flavor theory, then of the η and a0 mesons in QCD with up, down and strange quarks. In the longer term, the same methods will be applied to the baryonic sector.