Light Higgsinos at the ILC: Precision Measurements and Detector Requirements

Sert, Hale

Report/Dissertation / PhD Thesis

PUBDB-2016-00621

Light Higgsinos at the ILC: Precision Measurements and Detector Requirements

Sert, H. (Corresponding author)DESY*

2016
Verlag Deutsches Elektronen-Synchrotron Hamburg

Hamburg : Verlag Deutsches Elektronen-Synchrotron, DESY-THESIS 271 pp. (2016) [10.3204/DESY-THESIS-2016-001] = Universität Hamburg, Diss., 2015

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Please use a persistent id in citations: doi:10.3204/DESY-THESIS-2016-001

Report No.: DESY-THESIS-2016-001

Abstract: This thesis is based on a study of Natural Supersymmetry (SUSY) scenarios at the International Linear Collider (ILC). These scenarios are motivated by naturalness, which requires the mu parameter to be at the electroweak scale. The considered Natural SUSY scenario contains three light higgsino-like charginos and neutralinos with a mass splitting of a few GeV or even sub-GeV, while all other supersymmetric particles are heavy in the multi-TeV scale. Due to the small mass difference of a few GeV, the final state consists of a large missing energy and a few very soft visible particles. Therefore, the analysis of such scenarios is extremely challenging for the LHC as well as the ILC. In order to investigate the feasibility of observing light higgsinos at the ILC, an analysis has been performed using both fast detector simulation and full detector simulation for International Large Detector (ILD). The fast simulation results have indicated that the key observables of the higgsinos can be reconstructed with an uncertainty of a few percent. It has been shown that the results enable determining the lower limits and allowed regions for the mass parameters of the bino M1 and the wino M2, as well as determining the higgsino mass parameter µ to the accuracy of a few percent. The full simulation analysis has provided information about detector requirements, such as the identification of low momentum electrons and muons. The electron identification can be studied by using the ionisation energy loss of the particles per length, dE/dx, which can be obtained from the Time Projection Chamber (TPC) of ILD. The identification of low momentum muons has been studied in the context of the thesis by using the calorimeter cluster shape differences between muons and pions. As a result, a method has been developed for particles with momentum lower than 2 GeV, and its impact on the higgsino analysis has been investigated. It has been found that assuming the electrons can be identified with the same efficiency as the muons, the key observables can be reconstructed with the same precision as in the fast simulation case by taking two times more data.The presence of soft final-state particles makes the tracking of high relevance for the analysis. Therefore, a comprehensive hardware study related to the TPC of ILD has been performed. In this study, three commonly used gas mixtures have been investigated in a small gas chamber containing a triple Gas Electron Multiplier stack, and their performance has been compared. This study has enhanced the understanding of the dependency of the charge transfer on the gas type. It has confirmed that the gas proposed to be used in the TPC is the most promising one.

Note: Universität Hamburg, Diss., 2015

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