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Electrons from beauty-hadron decays in central Pb-Pb collisions at √s NN = 2.76 TeV

Völkl, Martin

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Abstract

Heavy quarks (charm and beauty) are an important probe for the characterization of the quark-gluon plasma (QGP), a state of color deconfined, hadronic matter. Experimentally, the QGP is produced in ultrarelativistic heavy-ion collisions, where heavy quarks are automatically generated and interact with the produced medium. Within this work, the properties of the beauty quarks in the medium are measured via the semileptonic decays of the associated hadrons. The measurement is based on the particle identification and tracking capabilities of the ALICE detector at the LHC. The separation of eletrons from beauty-hadron decays from the abundant background electrons is achieved using fits of the impact parameter distribution based on templates from Monte Carlo simulations. This approach makes use of the comparatively large decay length of the beauty hadrons ($c\tau \approx 500~\mu \rm{m}$). The large particle multiplicities in central Pb--Pb collisions at \PbPbEnergy~ create a particularly challenging environment for the measurement. The determined nuclear modification factor hints at values above unity for low transverse momenta of the electrons. In this region, the beauty quarks may participate in the collective motion of the medium. The nuclear modification factor decreases towards larger \pt, where an energy loss of the partons in the medium is expected. The measured range of $1.3<\pt<8~\GeVc$ also represents a region where contributions from both radiative and collisional interactions with the medium can contribute and is thus particularly interesting for the understanding of the interaction of heavy quarks with the medium.

Item Type: Dissertation
Supervisor: Stachel, Prof. Dr. Johanna
Date of thesis defense: 28 October 2016
Date Deposited: 16 Nov 2016 08:18
Date: 2016
Faculties / Institutes: The Faculty of Physics and Astronomy > Institute of Physics
Subjects: 530 Physics
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