Reconstruction of leptonic physic objects at future e+e- Higgs factory

Abstract : The Standard Model of elementary particle interactions is the outstanding achievement of the past forty years of experimental and theoretical activity in particle physics. Since the discovery of the Higgs boson in 2012 by the experiments at the Large Hadron Collider (LHC), the precise measurement has become the issue in high energy physics experiments.Many electron-positron Higgs factories with better accuracy on the Higgs total width measurements have been proposed, including the International Linear Collider (ILC) and the Circular Electron Positron Collider (CEPC).The Higgs physics program to be carried out at the future $e^{+}e^{-}$ colliders have been be evaluated and its extent of the precision of many of couplings are estimated to percent or sub-percent levels.In order to achieve this precision, the Particle Flow Algorithm (PFA) has become the paradigm of detector design for the high energy frontier. The key idea is to reconstruct every final state particle in the most suited sub-detectors, and reconstruct all the physics objects on top of the final state particles. The PFA oriented detectors have high efficiency in reconstructing physics objects such as leptons, jets, and missing energy.The lepton identification is essential for the physics programs, especially for the precise measurement of the Higgs boson.In this thesis, a PFA based lepton identification (Lepton Identification for Calorimeter with High granularity) has been developed for detectors using high granularity calorimeters. Using the conceptual detector geometry for the CEPC and single charged particle samples with energy larger than 2 GeV, LICH identifies electrons/muons with efficiencies higher than 99.5% and controls the mis-identification rate of hadron to muons/electrons to better than 1%/0.5%. Reducing the calorimeter granularity by 1-2 orders of magnitude, the lepton identification performance is stable for particles with E > 2 GeV. Applied to fully simulated eeH/$mumu$ H events, the lepton identification performance is consistent with the single particle case: the efficiency of identifying all the high energy leptons in an event, is 95.5-98.5%.Except for e and $mu$, $tau$s are extremely intriguing physics objects as its Yukawa coupling to the Higgs boson is relatively large. Due to its rich decay products, properties such as the Higgs CP and EW parameters at the Z-factory can be precisely measured. The $tau$ decay in high energy colliders is tightly collimated and low multiplicity, which provide excellent signatures to probe. In this thesis, the H$rightarrow$ $tautau$ channels are analyzed in different Z decay modes with SM background taken into account and the combine final accuracy is expected to be 1.3%.
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Dan Yu. Reconstruction of leptonic physic objects at future e+e- Higgs factory. High Energy Physics - Experiment [hep-ex]. Université Paris-Saclay; Institute of high energy physics (Chine), 2018. English. ⟨NNT : 2018SACLX018⟩. ⟨tel-01852267⟩

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