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| Home > Publications database > From the Machine-Detector Interface to Electroweak Precision Measurements at the ILC — Beam-Gas Background, Beam Polarization and Triple Gauge Couplings |
| Home > Publications database > From the Machine-Detector Interface to Electroweak Precision Measurements at the ILC — Beam-Gas Background, Beam Polarization and Triple Gauge Couplings |
| Book/Dissertation / PhD Thesis | PUBDB-2019-03013 |
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2019
Verlag Deutsches Elektronen-Synchrotron
Hamburg
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Please use a persistent id in citations: doi:10.3204/PUBDB-2019-03013
Report No.: DESY-THESIS-2019-018
Abstract: The International Linear Collider (ILC) is a planned electron-positron collider with a first stage at a center-of-mass energy of 250 GeV. The electron beam will be polarized to 80% and the positron beam to 30%. This allows for very precise measurements of Standard Model (SM) parameters, and of properties of the Higgs boson as well as unique searches for physics beyond the SM. In particular, the ILC will provide unprecedented measurement precision on electroweak observables, aiming for up to 2 orders of magnitude better precision than previously achieved. This will provide a deep insight into the chiral structure of the SM and open an additional portal to physics beyond the SM.In this thesis, a new study at 250 GeV will be presented using a combined analysis of $W$- and $Z$-pair production, as well as single-$W$ production and 2-fermion final state. This analysis will provide a coherent extraction of the total cross sections and the left-right asymmetries of all considered channels, as well as anomalous Triple Gauge Couplings and the luminosity-weighted average polarization, which is used as the absolute scale calibration of the polarization for all physics analyses.This study shows that a relative uncertainty of a few permille for all these measurements is already feasible at the first stage of the ILC and that a polarized positron beam is essential for achieving this level of precision for the total cross section and the left-right asymmetry. Furthermore, systematic uncertainties including their correlations are considered in this analysis and their impact on the measurement precision on the electroweak observables will be presented.The simulation of the ILD detector concept is based on a detailed baseline design which considers many real-life details of the detector, the accelerator and their interface. One of these aspects is the requirement on the vacuum quality in the beam-pipe. In this context, interactions between the electron bunch of the ILC and the residual gas atoms in the interaction region of ILD, their pressure dependency and their impact on the detector was studied with Geant4-based simulations. This was motivated by a redesign of the forward region of ILD, due to two changes in the ILC baseline design which reduced the focal length of the final doublet and introduced an additional beam position monitor. A part of the required space for this was regained by removing an original foreseen vacuum pump at this location. In this thesis, it will be shown that beam-gas collisions constitute a non-negligible, but minor source of background even if the pump is removed.
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