Prospects for precision measurements of the Top-Yukawa Coupling and CP Violation in ttH Production at the CLIC e+e− Collider
High energy particle colliders provide unique facilities to investigate the physics that take place at the smallest scales. The thesis present works for both future and upgraded colliders. CLIC - the Compact Linear Collider - is a proposed high energy electron-positron collider with collision energies between 350 and 3000 GeV. The LHC is a high energy proton-proton collider at CERN operating at 13 TeV. Over the next few years, it will be upgraded to the High-Luminosity LHC to operate at higher luminosities. The thesis presents an analysis of the ttH¯ production at CLIC leading to predicted precisions on top -Yukawa coupling and constraints on the CP properties of the Higgs boson. The thesis also presents work for the ATLAS experiment investigating the suitability of new sensors for use in the HL-LHC and studies of physics processes. The predicted precision on the top -Yukawa coupling using the e+e− → ttH¯ process is measured to be 2.7% at √s =1.5 TeV at CLIC with polarised beams and an integrated luminosity of 2.5 ab−1 using the CLIC SiD detector model. The H → b¯b final state of the Higgs boson and the 6-jet and 8-jet final states are used for the analysis. A multivariate selection is used to separate the ttH¯ signal from the backgrounds. b-tagging information is observed to be the strongest variable in the multivariate selection. The CP-proprties of the top -Higgs coupling are also investigated at √s =1.5 TeV using CLIC machine. A Higgs boson containing a mixture of scalar and pseudoscalar components is characterised by a mixing angle, φ. The precision of the mixing angle φ is determined to be ∆ sin2 φ ≃ 0.07 with cross-section measurements from both 6-jet and 8-jet final states. The results can be further improved up to ∆ sin2 ≃ 0.03 with an additional angular distribution, up-down asymmetry, in the semi-leptonic channel. The ATLAS experiment is upgrading its Inner Detector (ID) to an all-silicon system, the Inner Tracker (ITk). A new Front End chip, RD53A, has been developed using 65 nm CMOS technology. The thesis presents the work on the procedure of setting up the test for the RD53A chip by using testbeam at DESY with EUDET telescope. The EUTelescope software is used to reconstruct the tracks of particles and the TBMon2 framework is used to do the final analysis for the testing module. With data collected in December 2018 at DESY testbeam facility, the residual of the UK RD53A module with cell size of 50×50 µm2 is found to be symmetrical with 50.7 µm in x-axis and 51.3 µm in y-axis. The hit efficiency is determined to be 97.651%±0.035% which passes the requirement for the HL-LHC.