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Mohit Sharma – Leptoquarks and Tau Leptons

Mohit Sharma received his MS Dual Degree in  Computational Natural Sciences (CNS). His research work was supervised by Dr. Subhadip Mitra. Here’s a summary of his research work on Discovery prospects of leptoquarks decaying into top quarks and tau leptons at the HL-LHC:

Leptoquarks (LQs) are hypothetical particles that connect the quark and the lepton sectors of the Standard Model (SM). As a result, the phenomenology of leptoquarks becomes very interesting and has been extensively studied in recent years. However, the majority of the recent attention is mainly due to their ability to explain the long-standing anomalies observed in B-meson decays and the muon anomalous magnetic moment measurements. Generally, the models explaining the anomalies contain LQs that couple with the third-generation quarks and leptons. This gives additional motivation to search for such LQs (commonly known as the third-generation LQs in the literature) at the Large Hadron Collider (LHC).

In this thesis, we explore a novel search strategy to efficiently identify third-generation scalar leptoquarks at 14 TeV High Luminosity (HL)-LHC with an integrated luminosity of 3 ab?1. LQs here decay to a top quark plus a tau lepton (tt) and carry a charge of either 1=3 (f1) or 5=3 (f5). Our analysis utilizes a combined signal which consists of events from both single and pair production channels of LQ to improve the discovery prospects. We have divided our search into different benchmark scenarios based on LQ branching fractions and lepton-quark coupling parameters. We make use of several opensource HEP packages to simulate the experiments. A Monte Carlo event generator called Madgraph is used to generate the signal and background processes at the leading order (LO) with higher-order corrections being applied to some of the processes. Parton showering and hadronization is performed using the Pythia package while the detector effects are simulated using Delphes. Once all the processes are generated, we introduce a series of event selection cuts that are optimized to retain events from both pair and single production processes while rejecting a majority of background events. Finally, we try to estimate the discovery reach and exclusion mass limits of scalar LQs projected at the HC-LHC integrated luminosity of 3 ab?1. Analysing the final result, we conclude that the overall HL-LHC reach goes beyond 1.09 (1.33) TeV for f1 with BR = 0.5 (1.0) and 1.33 TeV for f5 with BR = (1.0). 

In the first chapter, We begin our discussion with a brief introduction to the Standard Model (SM), we then talk about some of its limitations and mention a few beyond the SM (BSM) theories. The next chapter provides an overview of the experimental particle setup at the LHC along with a brief summary of jet reconstruction algorithms and jet grooming techniques. Chapter three mainly talks about the LQ phenomenology and model details while providing a sneak peek of a recent LQ search performed at the CMS. In the fourth chapter, we discuss different aspects of our analysis including the simulation setup and search strategy. Finally, we present the results and conclusions in the fifth chapter.