Cut Optimization for Feasibility study of Dark Matter in Di-leptons Final state and Qualification of Silicon Sensors for CMS Phase 2 Upgrade

Abstract

Standard Model lacks Dark Matter candidates, and hence, we need physics beyond Standard Model. WIMPs (Weakly Interacting Massive Particles) are proposed as potential candidates for Dark Matter by theories beyond the Standard Model. The production of WIMP pairs can be studied in collider experiments. In this thesis, we focus on two topics: In the first part of my thesis, I concentrated on investigating the cut optimization for feasibility study of Dark Matter in Di-leptons final state. This exploration involved various avenues, with particular emphasis on the mono-Z channel. It involves the creation of a Higgs boson from the fusion of gluons (g g). This Higgs boson then undergoes a series of transformations, eventually giving rise to Z boson and a pseudoscalar particle referred to as "a". The Z boson further decays into oppositely charged leptons, while the pseudoscalar "a" transforms into Dark Matter candidates. For the investigation of this process, we utilized the MadGraph5_aMC@NLO event generator to simulate collisions between protons at an energy of 13.6 TeV. To better understand this, I employed different criteria to distinguish between the desired signal and the background noise. This involved analyzing essential kinematic factors, including missing transverse energy (Emiss T ), angular separations (∆ϕ), (∆R) and invariant mass (M). I also find the significance of each variable. Towards the end, I assessed the overall significance by applying f inal criteria. This was followed by the computation of the signal significance using the formula S/√B. The outcome yielded a signal significance value of 0.45σ. In the second part of my thesis, I executed measurements using SQC setup at NCP for phase 2 upgrade. This study entailed an analysis of eight key parameters, categorized into global and strip parameters. The global parameters centered on two critical aspects: the relationship between leakage current and reverse bias voltage (IV), as well as the correlation between bulk capacitance and reverse bias voltage (CV). The data acquisition involved varying voltage levels, spanning from 0 to 1000 V for leakage current and 0 to 600 V for bulk capacitance. Meanwhile, the strip parameters encompassed coupling capacitance (CC), interstrip capacitance (Cint), v strip current (Istrip), polysilicon resistance (Rpoly), interstrip resistance (Rint), and dielectric current (Idiel). For the specific batch identified as 43264_2S_035, the resultant average values were as follows: a full depletion voltage of 228V, a polysilicon resistance of 1.45MΩ, a coupling capacitance of 137.33pF, and a strip current of −50.72pA. These measurements are within specification as laid down down by CMS [1]