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Search for direct production of charginos, neutralinos and sleptons in final states with two leptons and missing transverse momentum in pp collisions at root s=8TeV with the ATLAS detector
Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
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Number of Authors: 2886
2014 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 5, 1-52 p.Article in journal (Refereed) Published
Abstract [en]

Searches for the electroweak production of charginos, neutralinos and sleptons in final states characterized by the presence of two leptons (electrons and muons) and missing transverse momentum are performed using 20.3 fb(-1) of proton-proton collision data at root s = 8 TeV recorded with the ATLAS experiment at the Large Hadron Collider. No significant excess beyond Standard Model expectations is observed. Limits are set on the masses of the lightest chargino, next-to-lightest neutralino and sleptons for different lightest-neutralino mass hypotheses in simplified models. Results are also interpreted in various scenarios of the phenomenological Minimal Supersymmetric Standard Model.

Place, publisher, year, edition, pages
2014. no 5, 1-52 p.
Keyword [en]
Supersymmetry, Hadron-Hadron Scattering
National Category
Physical Sciences
Research subject
Physics
Identifiers
URN: urn:nbn:se:su:diva-105872DOI: 10.1007/JHEP05(2014)071ISI: 000336654400001OAI: oai:DiVA.org:su-105872DiVA: diva2:733109
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation
Note

AuthorCount:2886;

Available from: 2014-07-08 Created: 2014-07-07 Last updated: 2017-12-05Bibliographically approved
In thesis
1. Search for Weakly Produced Supersymmetric Particles in the ATLAS Experiment
Open this publication in new window or tab >>Search for Weakly Produced Supersymmetric Particles in the ATLAS Experiment
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University, 2014. 124 p.
Keyword
ATLAS, ATLAS experiment, supersymmetry, chargino, neutralino, physics analysis, LHC, Large Hadron Collider
National Category
Subatomic Physics
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-108060 (URN)978-91-7447-992-8 (ISBN)
Public defence
2014-11-14, sal FA32, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

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.

Available from: 2014-10-23 Created: 2014-10-08 Last updated: 2015-09-23Bibliographically approved
2. Search for Charginos and Sleptons in ATLAS and Identification of Pile-up with the Tile Calorimeter
Open this publication in new window or tab >>Search for Charginos and Sleptons in ATLAS and Identification of Pile-up with the Tile Calorimeter
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The standard model of particle physics (SM) describes the elementary particles and their interactions. Supersymmetry (SUSY), a symmetry beyond those included in the standard model could resolve some of the SM shortcomings. It can provide a candidate for Dark Matter and a solution to the hierarchy problem. The Large Hadron Collider (LHC) has the potential to produce the particles predicted by SUSY. This thesis presents two searches for SUSY particles in proton-proton collision data recorded by the ATLAS experiment.

The first search described in this thesis looks for direct production of chargino and slepton pairs in a final state characterized by the presence of two leptons and missing transverse energy. The second search looks for production of chargino pairs via vector boson fusion (VBF) in a final state containing of two leptons, two jets and missing transverse energy. This is the first attempt in ATLAS to search for supersymmetric particles produced via VBF. A possible observation of such process would prove that the exchanged neutralino is a Majorana particle. These analyses are done using L=20.3 fb-1 proton-proton collisions at √s=8 TeV collected in 2012. No significant excess over background is observed. New exclusion limits at 95% confidence level on chargino, neutralino and slepton masses and cross section for chargino pair production via VBF are set.

The energy measurements of the particles created in LHC collisions are performed by the ATLAS calorimeters. Energy deposits from different collisions in the same read-out window and in the same calorimeter channel (pile-up) can spoil the energy measurements by the calorimeter. It is shown that the quality factor computed offline for each collision and for each channel in the Tile Calorimeter (TileCal) can be used to identify channels that need a special treatment to account for large energy depositions from pile-up. Efficient criteria to detect pile-up in TileCal are proposed.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University, 2015. 193 p.
Keyword
ATLAS experiment, particle physics, high energy physics, supersymmetry, SUSY, beyond standard model, chargino, neutralino, slepton, vector boson fusion, VBF, Tile calorimeter, TileCal, pile-up, quality factor, Large Hadron Collider, LHC, CERN
National Category
Subatomic Physics
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-120018 (URN)978-91-7649-240-6 (ISBN)
Public defence
2015-10-08, lecture room FB52, AlbaNova University Center, Roslagstullsbacken 21, Stockholm, 14:00 (English)
Opponent
Supervisors
Available from: 2015-09-16 Created: 2015-08-31 Last updated: 2015-09-16Bibliographically approved

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Abulaiti, YimingÅsman, BarbroBendtz, KatarinaBessidskaia, OlgaBohm, ChristianClément, ChristopheEriksson, DanielGellerstedt, KarlHellman, StenJohansson, K. ErikJon-And, KerstinKhandanyan, HovhannesKim, HyeonKlimek, PawelLundberg, OlofMilstead, David A.Moa, TorbjörnMolander, SimonOhm, Christian C.Petridis, AndreasPlucinski, PawelRossetti, ValerioSilverstein, Samuel B.Sjölin, JörgenStrandberg, SaraTylmad, Maja
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