Model Selection for and Partial-Wave Analysis of a Five-Pion Final State at the COMPASS Experiment at CERN

The light-meson spectrum is an important ingredient to understand quantum chromodynamics, the theory of strong interaction at low energies, where quarks and gluons are confined into hadrons. However, measuring this spectrum experimentally is very challenging, due to the large number of overlapping resonances it contains. To disentangle this complicated spectrum, partial-wave techniques are used. At the COMPASS experiment at CERN, the light-meson spectrum is studied in diffractive dissociation reactions. One such reaction, π- + p→π- π+ π- π+ π- + p, puts the analysis methodology to the test, because the large number of final-state particles requires a dedicated model-selection procedure and introduces a complicated background situation. In this thesis, such a model-selection procedure is developed and verified on simulated events. In addition to finding a suitable model, it can be used to assess the reliability of the results. The model-selection procedure is then successfully applied to data from the COMPASS 2008 data-taking campaign. A partial-wave decomposition is performed using the selected model. The results are compared to partial-wave decompositions of other final states and good agreement is found.