Calibration of Hadronic Calorimeter Cells and New Physics Searches at the ATLAS experiment
by
AlbaNova C5:1007 - ELPA
AlbaNova Main Building
Abstract:
This thesis presents two studies performed with the ATLAS detector at the Large Hadron
Collider: a detector performance study of the ATLAS Tile Calorimeter E-cells and a search
for new phenomena in tt? + Eᴛᵐ ˢˢⁱ final states. The detector performance study characterizes the
energy response of the E-cells of the ATLAS Tile Calorimeter using isolated muons from
W→μν events collected in proton-proton collisions at a √s = 13.6 TeV during LHC Run 3.
The E-cells rely on a different energy calibration method from that of standard calorimeter
cells. The study employs a novel noise-subtraction method to extract the muon signal in
challenging high pile-up conditions. Data-to-simulation ratios are used to validate the energy
scale calibration and assess response uniformity across the detector modules, while dedicated
studies evaluate systematic effects of the noise-subtraction procedure. Year-to-year stability
measurements demonstrate that the calibration remains consistent throughout Run 3 in the
data-taking period 2022-2023. The search for new phenomena targets supersymmetric models
with direct production of stop-quark pairs decaying to top quarks and the lightest neutralino,
as well as dark matter models where a scalar or pseudoscalar mediator is produced in
association with a tt? pair. The analysis uses final states with exactly one lepton, jets, and large
missing transverse momentum in events from of proton-proton collisions at √s = 13 TeV
collected during LHC Run 2. Event classification is performed using neural network-based
discriminants trained separately for each signal model and kinematic category. No significant
excess above the Standard Model prediction is observed and exclusion limits are set on the
masses of the supersymmetric particles and dark matter mediators.