Ph.D. Thesis: Studies of Long-Lived Supersymmetric Top Quarks and Online Monitoring of the ATLAS First Level Calorimeter Trigger
by
Marianne Johansen(SU Fysikum)
→
Europe/Stockholm
FB42
FB42
Description
The Large Hadron Collider (LHC) has recently started colliding protons at 7 TeV centre-of mass
energy. Extensive searches for hitherto unobserved particles and physics processes will be made as
part of an ambitious scientific programme which aims to answer some of the fundamental questions
in modern physics. The ATLAS detector, designed to discover a wide range of physics processes,
will play a crucial part in these searches.
The First Level Calorimeter Trigger is one of the first steps in the ATLAS data acquisition
chain. Excellent performance at this stage is required to fully make use of the ATLAS potential for
discovery of new physics processes. Online monitoring of the First Level Calorimeter Trigger is
therefore of great importance to ensure good quality of data and correct performance of the trigger.
As part of the overall online trigger monitoring this thesis describes the monitoring of the Jet/
Energy-sum Processor, responsible for defining the first jet candidates and summation of the total
energy deposited in the ATLAS calorimeters.
Supersymmetry is one of the most studied models of physics beyond the Standard Model.
Some supersymmetric models give rise to long-lived stop squarks or gluinos which, if produced
at the LHC, immediately will form exotic hadrons, called R-hadrons. The discovery or nondiscovery
of R-hadrons can provide important information about physics beyond the Standard
Model and searches for these particles are therefore a part of the ATLAS scientific programme.
This thesis investigate the capability of the ATLAS detector to discover stop R-hadrons using
different track configurations and ß measured by the calorimeters. A technique for measuring the
R-hadron mass using time-of-flight information from the ATLAS muon detectors is demonstrated
as well. Included in this thesis is also a phenomenological study of the possibility for a long-lived
stop squark to arise in supersymmetric models where the neutralino is the lightest supersymmetric
particle. The conditions for the stop to be long-lived as well as the implications it has on the dark
matter density and the supersymmetric mass spectra are studied in detail.