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[PAST EVENT] Physics Colloquium - Boris Grube
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Boris Grube, Technical University of Munich, Title of Talk: Searching for exotic forms of hadronic matter at the COMPASS experiment
Abstract:
Quantum Chromodynamics (QCD) describes the interaction of quarks via the exchange of gluons. A remarkable feature of QCD is that also the gluons, i.e. the force mediators, carry the charges of the strong interaction and hence do self-interact. At low energies, this leads to the phenomenon of confinement, e.g. the entrapment of quarks and gluons into composite particles, the hadrons.
Although the QCD equations are simple to write down, they are very hard to solve in the confinement regime. A quantitative understanding of the phenomenon of confinement still poses considerable theoretical and experimental challenges and is one of the key issues in particle physics.
The study of the excitation spectrum of hadrons has provided essential clues that helped to develop QCD, but also still leaves a number of deep puzzles. In the constituent quark model, hadrons are either combinations of three quarks, which are called baryons, or quark-antiquark states, which are called mesons. However, QCD in principle allows for more complicated hadronic states like multi-quark states (e.g. molecule-like objects), states with excited gluonic fields (hybrids), or even purely gluonic bound states (glueballs).
The hunt for these so-called exotic hadrons is a world-wide experimental effort. The COMPASS experiment at CERN has collected world-leading datasets that allow us to study the spectrum of mesons that are composed of the three lightest quarks (up, down, and strange) with unprecedented detail and precision. I will present selected results from the analysis of these data with a focus on the search for exotic mesons.