Search for Weakly Produced Supersymmetric Particles in the ATLAS Experiment

• Main Author: Tylmad, Maja
• Format: Doctoral Thesis
• Language: English
• Published: Stockholms universitet, Fysikum 2014
• Subjects: ATLAS; ATLAS experiment; supersymmetry; chargino; neutralino; physics analysis; LHC; Large Hadron Collider
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-108060; http://nbn-resolving.de/urn:isbn:978-91-7447-992-8

The Large Hadron Collider located at CERN is currently the most powerful particle accelerator and ATLAS is an experiment designed to exploit the high energy proton-proton collisions provided by the LHC. It opens a unique window to search for new physics at very high energy, such as supersymmetry, a postulated symmetry between fermions and bosons. Supersymmetry can provide a solution to the hierarchy problem and a candidate for Dark Matter. It also predicts the existence of new particles with masses around 1 TeV, thus reachable with the LHC. This thesis presents a new search for supersymmetry in a previously unexplored search channel, namely the production of charginos and neutralinos directly decaying to electroweak on-shell gauge bosons, with two leptons, jets, and missing transverse momentum in the final state. The search is performed with proton-proton collision data at a center of mass energy of √s = 8 TeV recorded with the ATLAS experiment in 2012. The design of a signal region sensitive to the new signal is presented and a data driven technique to estimate the Z+jets background is developed. Precise measurements of hadronic jet energies are crucial to search for new physics with ATLAS. A precise energy measurement of hadronic jets requires detailed knowledge of the pulse-shapes from the hadron calorimeter signals. Performance of the ATLAS Tile Calorimeter in this respect is presented using both pion test-beams and proton–proton collision data. === <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2 and Paper 4: Technical report from the  ATLAS experiment.</p>