Enhancing searches for supersymmetric-top pairs using Higgs tagging at 13 TeV

Abstract

Supersymmetry is one of the Beyond Standard Model theories which is postulated to resolve some of the gaps in the Standard Model. It predicts a partner particle for every SM particle and these new particles are expected to be massive. If they are accessible at the LHC, they can be produced in pp collisions and searching for these particles is one of the primary goals of the ATLAS and CMS experiment. There is a strong motivation to look for supersymmetric partner of the SM top quark, since its existence will help stabilize the divergent correction to Higgs mass where the maximum contribution comes from the massive top quark. There are existing analyses which search for particles in a variety of final state signatures. This thesis presents a search for pair produced stop quark in single lepton final state and in fully hadronic final state along with large missing transverse momentum and multiple b-jets.

This thesis targets a SUSY model which has a Higgs boson in the decay cascade of the pair produced stop particle. This model is not extensively studied at the CMS experiment and can be an interesting channel to look for SUSY with Higgs boson in the final state. Kinematic variables are used to reduce background events and maintain signal events as much as possible. The mass spectra of the SUSY particles, which are free parameters of the theory determines the kinematics of the various particles in the event, including the Higgs boson. The Higgs particle is reconstructed in two categories, tagged and resolved for high and low momentum Higgs respectively. The performance of the analysis is studied with additional tagged Higgs as compared to the traditional baseline event selections. Limits are obtained at 95% confidence level as a function of the mass of stop for different model scenarios at luminosity L = 150 /fb of simulated data at 13 TeV centre of mass energy in the CMS detector configuration.