The Upgraded Outer Tracker for the CMS Detector at the High Luminosity LHC, and Search for Composite Standard Model Dark Matter with CMS at the LHC

The Standard Model of particle physics describes the interactions between particles at the smallest known scale. The Standard Model has passed many tests with flying colours, but several observations, such as the need for dark matter, do not find an explanation in this framework. The Large Hadron Collider (LHC) at CERN is an excellent tool to study the Standard Model and to try and find answers to the open questions. The LHC collides protons resulting in a center of mass energy of 13~TeV, the highest energies ever attained at a particle collider. This enables physicists to study matter at an energy scale which is normally not accessible and which reflects the energy density in our Universe a fraction of a second after the Big Bang. At one of the four interaction points along the LHC, the Compact Muon Solenoid (CMS) experiment is located. This general purpose experiment is designed to give an as good as possible measurement of the kinematic properties of the particles produced in a collision. CMS does this by using several subdetectors, one of which is the tracking system. The CMS tracker is based on silicon technology and consists of a pixel and a strip detector, designed to reconstruct the tracks of charged particles. The strip detector has been taking data since the start of the operation of the LHC in 2010 and will continue to do so until 2024. During the 2025-2027 Long Shutdown of the LHC, the accelerator complex will be upgraded to start the High Luminosity LHC (HL-LHC) phase at the end of 2027, which will provide the experiments with higher luminosities by increasing the number of proton-proton collisions per bunch crossing (pileup). In order to keep tracking performance at pre-HL-LHC levels in this harsher HL-LHC environment, the strip tracker will be replaced by an Outer Tracker, consisting of pixel-strip (PS) and strip-strip (2S) modules. These modules have local track reconstruction logic. The output of this logic is used as input to the L1 trigger system. This thesis consists of a hardware part, focussing on the testing of Outer Tracker prototypes, and a search for new physics using the data collected by the CMS experiment. $\\$ $\textit{The Upgraded Outer Tracker for the CMS Detector at the High Luminosity LHC: }$ $\\$Over the past years, Outer Tracker prototype ASICs and modules have become available. These require a dedicated test bench for characterization. This thesis discusses in detail the Phase-2 Outer Tracker and the structure and scope of the firmware project ($\mu$DTC) set up to read out ASIC and module prototypes of this new detector. The test bench is designed to test both 2S and PS modules and components. Several tests, to which the author contributed, are presented, going from bench-top testing of single ASICs, through radiation hardness testing of these chips and operating module prototypes in test beams. $\\ \textit{Search for Composite Standard Model Dark Matter with CMS at the LHC:}$ $\\$ The Sexaquark (S), composed of uuddss quarks, is a hypothetical particle that was proposed to be stable and a potential dark matter candidate. $\bar{S}$ particles could be produced in the proton-proton collision and could subsequently annihilate on a neutron in the beampipe or detector material. This annihilation could result in a $\mathrm{K_S^0} + \bar{\Lambda}^0)]$ which in turn can decay to charged products which are reconstructable with the CMS tracker. This is the signal used in this thesis to look for the $\bar{S}$ in the CMS 2016 dataset by reconstructing the $\bar{S}$ kinematic properties and its annihilation vertex. The difficulties of reconstructing such a low momentum, displaced and off-pointing signature with the default CMS reconstruction algorithms will be studied and a first-ever limit on the $[\sigma(\mathrm{p+p} \rightarrow \mathrm{\bar{S}}) \times \sigma(\mathrm{\bar{S}} + \mathrm{n} \rightarrow \mathrm{K_S^0} + \bar{\Lambda}^0)]$ cross section will be presented.