Exploring top pair decay with the ATLAS Open Data

Abstract

This thesis aims to reproduce the ATLAS detector measurements of the top quark mass, which is done by removing background events in the ATLAS detector dataset that has been extracted from the ATLAS Open Data (AOD). Understanding how it is produced and decayed, and how it can be seen in the detector. The coding for this project was done in ROOT via C++. We used simulations and a theoretical background to make the necessary cuts to isolate and measure the top quark’s essential properties. The obtained value was taken without neutrino analysis, as it was assumed that the neutrino had zero momentum and energy. The conditions that were made to isolate the top quark have isolated 150 top quark-like events, of which only 14 came from a semi-leptonic decay channel from the top quark.

Popular Abstract

The discovery of the top quark was an essential achievement for particle physics due to its crucial role in completing the SM of particle physics, as it has been developed to understand the interactions of elementary particles. The SM describes the elementary particles and their interactions. The SM consists of three generations of quarks (up, down), (charm, strange), (top, bottom), and three generations of leptons (electron, electron-neutrino), (muon, muon-neutrino), (tau, tau-neutrino), gauge bosons (gluon, photon, Z, W) and scalar boson (higgs). The bottom quark, which is in the third quark generation, was discovered in 1973. As the up-quark and down-quark are in the first generation, and the charm-quark and strange-quark are in the second generation, it got us thinking that the bottom quark has to be partnered with another quark, the top quark. No such particle was seen in the detector at that time, which led to the theory that the top quark was very heavy, which is why it had not been seen in the detector. A high proton collision energy is needed for the heavy top quark to be produced. Because the top quark has a large mass, we know that it has to decay very rapidly. Therefore, the top quark itself can not even be seen directly in the detector, but its decay product can. We are faced with two very big problems: We need high-energy proton collisions, which could be achieved by having a large ring for the particle accelerator, increasing particle precision, and having stronger magnets (to accelerate charged particles such as protons). We also need to make theoretical calculations for the possible Feynman diagrams for the decay of the heavy top quark, Monte Carlo (MC) simulations were heavily used in that stage. It is an excellent tool for simulating a heavy quark decay
using theoretical particle physics. MC simulates the top quark decay event many times and adjusts the values to give the most probable event. Fermilab is a major laboratory of particle physics; it had the Tevatron particle accelerator, which was the most powerful particle accelerator before the LHC was operational. Fermilab has upgraded the Tevatron particle accelerator technology, such as better precision and advances in superconducting magnets, to get stronger magnets. This is done to get high enough proton collision energies to produce the top quark, and with the help of the simulations, the top quark was produced, and its decay products were detected, and the top quark was discovered in the CDF detector in 1995, in collaboration with the D0 detector group at Fermilab. From these advances, more BSM physics is being done to enhance our understanding of particle interactions. By understanding particle physics, we can all discover new particles by using ATLAS Open Data as the ATLAS experiment releases its dataset for different energies, so that anyone, even people outside of academia would be able to have access to the dataset to analyze and make new advances to all branches of physics.

• author: Kattaya, Samuel
• supervisor: Else Lytken
• organization: Particle and nuclear physics; Department of Physics
• course: FYSK04 20251
• year: 2025
• type: M2 - Bachelor Degree
• subject: Physics and Astronomy
• language: English
• id: 9210815
• date added to LUP: 2025-08-28 10:27:50
• date last changed: 2025-08-28 10:27:50