Investigating Charm Quark Fragmentation Properties at the LHC: A Crucial Step Towards New Physics Discovery at the High-Luminosity Large Hadron Collider.

Studying the fascinating proton-proton collision events generated by CERN's Large Hadron Collider provides a promising approach to tackling some of the most challenging mysteries in particle physics. These include the absence of viable dark matter candidates, insufficient explanations for the observed matter-antimatter asymmetry in the early Universe, the vast range of quark and lepton masses, and the disparity in the strength of gravity compared to other fundamental forces. Recent discoveries, such as the Higgs boson, offer crucial clues that could help to resolve these issues. To maximize the collider's discovery potential, the Large Hadron Collider and its experiments are undergoing significant upgrades to become the High-Luminosity Large Hadron Collider (HL-LHC). Scheduled to begin operation in 2029, the HL-LHC's data is expected to provide vital insights into these pressing physics problems. However, as data collection increases, it becomes more challenging to interpret the resulting physics outcomes. Prospect studies for the HL-LHC reveal that most measurements of the Higgs boson's properties will be limited by theory uncertainties arising from the modeling of signal and background processes using Monte Carlo simulation packages. Consequently, it is an ideal time to perform crucial measurements of well-established Standard Model processes. Such measurements are essential in minimizing experimental and theory uncertainties and achieving the required precision necessary for detecting new physics phenomena at the HL-LHC. This proposal aims to contribute to the understanding of charm quark fragmentation properties at the LHC by analyzing proton-proton collision data collected by the ATLAS experiment in Run 2 and Run 3. The project will conduct a comprehensive study of charm quark-initiated jets, which is crucial in reducing both theory and experimental uncertainties for searches related to new physics processes. Specifically, this project will focus on improving searches with experimental signatures involving charm quarks, such as H→cc searches. The proposal seeks to measure key parameters such as the charm quark fragmentation function and the D+ and D*+ meson fragmentation fractions, while also providing a clean dataset of charm quark-initiated jets to enhance the precision of the machine learning-based jet flavor tagging algorithms in ATLAS. Fragmentation and hadronization properties of quarks and gluons are governed by non-perturbative Quantum Chromodynamics (QCD). However, calculating these processes from first principles is prohibitively computationally complex, and the precise physics processes governing them are not entirely understood. Therefore, achieving the desired precision in predicting these processes relies heavily on experimental data. Despite their crucial role in searching for new physics, the properties of charm jets have not yet been studied in detail at the LHC. This proposal aims to launch a broad scientific program, lasting beyond the lifetime of the project, to gain a better understanding of the Standard Model processes governing their properties. The project is expected to last three years and will be incorporated into a young researcher's PhD thesis.