Quarkonium Polarization: Victor Hesspreis 2015 geht an Valentin Knünz

2015-08-31 Georg Pühringer

Dr. Valentin Knünz vom Institut für Hochenergiephysik in Wien erhält den Viktor Hess Preis der Österreichischen Physikalischen Gesellschaft. Ausgezeichnet wird Herrn Knünz Dissertation mit dem Titel "Measurement of Quarkonium Polarization to Probe QCD at the LHC". Viktor Hess hat im Jahre 1912 die Höhenstrahlung entdeckt und wurde im Jahr 1936 dafür mit dem Nobelpreis für Physik ausgezeichnet.

Titel: Measurement of quarkonium polarization to probe QCD at the LHC

Abstract: The Large Hadron Collider at CERN provides excellent conditions for studies of hadron formation through measurements of quarkonium production. Until quite recently, experimental and phenomenological efforts have not resulted in a satisfactory overall picture of quarkonium production cross sections and quarkonium polarizations, challenging QCD-inspired models. The CMS detector is ideally suited to study quarkonium production in the experimentally very clean dimuon decay channel, allowing precision measurements of the polarizations of the S-wave bottomonium and charmonium states. Surprisingly, no significant polarizations are found in any of the studied quarkonium states, in none of the studied reference frames, nor in a frame-independent analysis. From an experimental point of view, these results, together with recent results from other experiments, clarify the confusing picture originating from previous measurements, which were plagued by experimental ambiguities and inconsistencies. The currently most favored approach to model and understand quarkonium production is non-relativistic QCD (NRQCD), which allows color-octet pre-resonant quark-antiquark states to contribute to quarkonium bound state formation. A large sample of LHC measurements in the field of quarkonium production is interpreted with an original phenomenological approach within the theoretical framework of NRQCD. This phenomenological analysis leads to a coherent picture of quarkonium production cross sections and polarizations within a simple model. These findings provide new insight in the dynamics of heavy quarkonium production at the LHC, an important step towards a satisfactory understanding of hadron formation within the standard model.