Tracking mesons: Rare species and hidden properties- New precision measurements with the COMPASS experiment at CERN

Abstract
Even half a century past the first development of QCD the description of the excitation spectrum based on quarks and gluons as fundamental building blocks of matter is still a challenge. This not only concerns theoretical physics but also the experiments often cannot give clear and solid information about the existence and properties of ground state excitations. As so often, progress can only be reached by major advancements on what concerns either energy or precision. The COMPASS experiment at CERN adresses many open questions on the properties of hadrons, among them is the search for new excitations involving quarks and gluons. The presentation will give an overview on new results in the field of light mesons. As an example we will discuss how a pion deforms under the influence of a strong electromagnetic field. We also show, how new methods of analysis allow deeper insights into the spectrum of hadrons. Surprises may then have to be expected.