Dilepton spectroscopy with HADES.
Technische Universität, Darmstadt
[Ph.D. Thesis], (2004)
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|Item Type:||Ph.D. Thesis|
|Title:||Dilepton spectroscopy with HADES|
The dilepton spectrometer HADES (High Acceptance Dielectron Spectrometer) has started recently its operation at the SIS accelerator in Gesellschaft fuer Schwerionenforschung (GSI), Darmstadt, and several commissioning beamtimes have been performed. In this work, the analysis of data measured in November 2001, where collisions of 12C projectiles on a carbon target at a beam energy of 2AGeV have been studied, is presented. About 35 millions of events with multiplicity of charged particles larger or equal to one have been selected for the analysis. The main motivation of this work is to reconstruct the invariant-mass spectrum of the produced e+e- pairs. The main sources of dilepton production are pi0 decays. The highest branching ratio has: a) pi0 to gamma+ gamma (BR=98.8%) and b) pi0 to gamma and e+e- (BR=1.2%). In matter the produced photons can convert to e+e- pairs: gamma to e+e-. Due to small averaged opening angles alpha= =2.4 deg. most of the conversion pairs are not resolved as two individual tracks in the detectors in the front of the HADES magnet. These unresolved pairs contribute as single tracks to the combinatorial background. Full-scale simulations based on the UrQMD model have been performed to study the detector properties and analysis performance. The lepton tracks have been identified. The topology of the MDC hits has been studied for lepton tracks and unresolved close pairs tracks. A method of close pairs rejection has been developed. The analysis steps for lepton and dilepton identification are discussed in detail, and spectra for each analysis step are presented. The reconstructed e+e- spectrum from measured data is compared with the spectrum from the analysis of simulated data.
|Place of Publication:||Darmstadt|
|Uncontrolled Keywords:||dileptons, HADES, e+e- pairs, heavy ion physics|
|Divisions:||05 Department of Physics|
|Date Deposited:||17 Oct 2008 09:21|
|Last Modified:||07 Dec 2012 11:50|
|Referees:||Nörenberg, Prof. Dr. W.|
|Advisors:||Braun-Muzinger, Prof. Dr. Peter|
|Refereed:||29 April 2004|