Supersymmetry search via excess of top quarks events

Supersymmetry (SUSY) is an extension candidate for the Standard Model. It offers solutions to many problems in the Standard Model. It is proposed that there is a new copy of Standard Model particles with spin differ by ½. These particles are unstable and very massive, and will decay into Standard Model particles. In this thesis, the selection cuts for SUSY signal at LM9 test point has been developed. Various variables are studied for their characteristic against signal and different backgrounds. The selection has been optimized to give a better signal to backgrounds ratio. The backgrounds used in the thesis consist of top events, QCD events, and Electroweak events. All samples are simulated by Monte Carlo simulation and normalized to 183 pb-1 integrated luminosity.

超对称（Supersymmetry, SUSY）是标准模型（Standard Model）的候选扩展理论，可为标准模型现存的诸多问题提供解决方案。该理论预言存在一类与原标准模型粒子自旋相差½的全新粒子副本，此类粒子极不稳定且质量极高，最终将衰变为标准模型粒子。本论文针对LM9测试点处的超对称信号构建了筛选截断方案，研究了多种变量在区分信号与各类本底时的特性，并对该筛选方案进行优化以获得更优的信号与本底比值。本论文所使用的本底样本包含顶夸克事例、量子色动力学（Quantum Chromodynamics, QCD）事例与电弱（Electroweak）事例，所有样本均通过蒙特卡洛（Monte Carlo）模拟生成，并归一化至183 pb⁻¹的积分亮度。