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Jet Physics with A Large Ion Collider Experiment at the Large Hadron Collider

Klein, Jochen

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In the presence of the strongly-interacting medium created in relativistic heavy-ion collisions, highly energetic partons from hard interactions lose energy through scattering and radiating. This effect, referred to as jet quenching, is observed as a suppression of particles with large momenta transverse to the beam axis (high-pt). To study the impact of the medium evolution on the energy loss modelling in the Monte Carlo event generator JEWEL, we compare results obtained for different scenarios of Au–Au collisions at sqrt(s_NN) = 200 GeV. For this purpose, JEWEL was extended to use the output of relativistic hydrodynamic calculations in the OSCAR2008H format. We find the modelling of common observables, e.g. the nuclear modification factor, to be rather insensitive to the details of the medium evolution, for which the analytically accessible Bjorken expansion can thus be considered adequate. The OSCAR interface now allows further studies also at LHC energies.

Jets of large transverse momentum are interesting yet rare probes. An online selection of relevant events is required to accumulate sufficient statistics in the experiments. Such a trigger was implemented into the Transition Radiation Detector (TRD) of ALICE. It requires the presence of several geometrically close high-pt tracks. In the first LHC run, the operation of the TRD trigger comprised the preparation of the front-end electronics and the commissioning of the online tracking to ensure reliable data taking. From 2012 onwards, the TRD triggers were operated successfully in pp collisions at sqrt(s) = 8 TeV and sqrt(s) = 2.76 TeV as well as p–Pb collisions at sqrt(s_NN) = 5.02 TeV. The recorded data show no bias in the measured spectra and fragmentation functions for charged jets with transverse momenta above ~100 GeV/c.

The response of the medium to a traversing parton was studied by the measurement of correlations between a trigger jet and associated hadrons. Different proton abundances in jets and medium hadronization motivate the comparison of inclusive and proton associates, which is possible with the particle identification capabilities of ALICE. The measurements of jet-hadron and jet-proton azimuthal correlations in Pb–Pb collisions at sqrt(s_NN) = 2.76 TeV show a reduced proton yield in the near-side (Dphi = 0) peak. The away-side (Dphi = pi) peaks are consistent with each other even though a reduced proton yield seems to be favoured in the analyzed data set. A more conclusive statement on this result will require the analysis of further data with higher statistics.

Item Type: Dissertation
Supervisor: Stachel, Prof. Dr. Johanna
Date of thesis defense: 12 November 2014
Date Deposited: 19 Nov 2014 07:52
Date: 2014
Faculties / Institutes: The Faculty of Physics and Astronomy > Institute of Physics
Subjects: 530 Physics
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