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| Book/Report/Dissertation / PhD Thesis | PUBDB-2018-01897 |
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2018
Verlag Deutsches Elektronen-Synchrotron
Hamburg
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Please use a persistent id in citations: doi:10.3204/PUBDB-2018-01897
Report No.: DESY-THESIS-2018-012
Abstract: The International Linear Collider (ILC) is a planned electron-positron collider, which will enable high precision measurements of Standard Model (SM) observables, as well as direct searches for new particles beyond the SM. Particle Flow (PFlow) is a key concept for reaching the required level of precision at the ILC; one of its main aspects is that the energy of each particle should be determined in the optimal detector sub-component.The International Large Detector (ILD) is one of the two detector concepts proposed at the ILC. It was designed according to the principles of PFlow and constitutes the experimental context of this thesis. The precision of the PFlow approach is limited by the confusion that can occur when reconstructing high energy events with a large particle multiplicity. Detector simulations are used to do physics- as well as detector optimisation studies. While the full simulation presents a comprehensive description of the detector with a high level of realism, it is computationally expensive. Studies promptly requiring a large number of simulated events are only feasible by using a fast simulation, which uses a slightly simplified detector description. SGV is the fast detector simulation chosen for ILD. By default, it does not emulate the confusion effects.The impact of this simplification on the PFlow performance of SGV was investigated in this thesis. After the implementation of a Particle Flow confusion emulation routine in SGV (SGV-PFL), its performance was evaluated and compared to the full simulation. With its default settings, the Particle Flow performance of SGV is up to 30% more optimistic than the full simulation. However, with the confusion implementation, the SGV-PFL performance was on average 55% worse. The Particle Flow performance of SGV-PFL was further studied in the context of an NUHM supersymmetry scenario that considers the pair production of gauginos at the ILC. The $\tilde{\chi}^{\pm}_{1}$ and $\tilde{\chi}^{0}_{2}$ are assumed to be nearly mass degenerate and decaying into $W^{\pm} \tilde{\chi}^{0}_{1}$ and $Z^{0} \tilde{\chi}^{0}_{1}$, respectively. As a challenge for the Particle Flow reconstruction, the hadronic decays of the gauge bosons were chosen as signal. The performed analysis focused on determining the masses of the three gauginos and the cross-sections of the two signal processes. The same analysis methods were applied independently on Monte Carlo data produced both with the full simulation and with SGV-PFL. The resulting masses and cross-section values were compared. It was concluded that the large discrepancy between SGV-PFL and the full simulation Particle Flow performance is not perceptible on an analysis level. The effect is obscured by much more prominent contributions from the jet clustering and jet-pairing effects.
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