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Search for Weakly Produced Supersymmetric Particles in the ATLAS Experiment
Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
2014 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
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.

sted, utgiver, år, opplag, sider
Stockholm: Department of Physics, Stockholm University , 2014. , s. 124
Emneord [en]
ATLAS, ATLAS experiment, supersymmetry, chargino, neutralino, physics analysis, LHC, Large Hadron Collider
HSV kategori
Forskningsprogram
fysik
Identifikatorer
URN: urn:nbn:se:su:diva-108060ISBN: 978-91-7447-992-8 (tryckt)OAI: oai:DiVA.org:su-108060DiVA, id: diva2:753514
Disputas
2014-11-14, sal FA32, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:00 (engelsk)
Opponent
Veileder
Merknad

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2 and Paper 4: Technical report from the  ATLAS experiment.

Tilgjengelig fra: 2014-10-23 Laget: 2014-10-08 Sist oppdatert: 2015-09-23bibliografisk kontrollert
Delarbeid
1. Pulse shapes for signal reconstruction in the ATLAS Tile Calorimeter
Åpne denne publikasjonen i ny fane eller vindu >>Pulse shapes for signal reconstruction in the ATLAS Tile Calorimeter
2010 (engelsk)Inngår i: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 617, nr 03-jan, s. 96-98Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

The ATLAS detector will record proton-proton collisions produced in the Large Hadron Collider at center of mass energies of up to 14 TeV. Its design allows for precision measurements as well as searches for new physics. Energy measurement using the calorimeters is crucial to these efforts. Studies of the pulse shapes used for signal reconstruction in the Tile Calorimeter are presented. The shapes were measured using test beam data and found to vary slightly with signal size. The impact of this variation on the reconstructed energy has been determined using a toy Monte Carlo.

Emneord
ATLAS, Calorimeter, Test beam, Pulse shape
HSV kategori
Identifikatorer
urn:nbn:se:su:diva-68183 (URN)10.1016/j.nima.2009.09.114 (DOI)000279258700026 ()
Merknad
authorCount :2Tilgjengelig fra: 2012-01-03 Laget: 2012-01-03 Sist oppdatert: 2017-12-08bibliografisk kontrollert
2. Measurement of the ATLAS Tile Calorimeter pulse-shapes with √s = 7 TeV collision data
Åpne denne publikasjonen i ny fane eller vindu >>Measurement of the ATLAS Tile Calorimeter pulse-shapes with √s = 7 TeV collision data
2010 (engelsk)Rapport (Annet vitenskapelig)
Abstract [en]

The energy reconstruction of the ATLAS Tile Calorimeter requires a predefined pulse-shape function. This pulse-shape function must match the pulse-shapes in data to avoid bias in the reconstructed energy. Using 60 nb-1 of √s = 7 TeV collision data, this note investigates deviations between measured pulse-shapes and the pulse-shape used for reconstruction and the possible bias on the energy reconstruction are studied. Measured pulse-shape widths exhibit slight channel-by-channel variations of the order ±1% with respect to the width of the reference pulse-shape. This implies less than 0.5% bias on the reconstructed energy. No energy dependence of the pulse-shapes is found.

Publisher
s. 22
HSV kategori
Identifikatorer
urn:nbn:se:su:diva-108041 (URN)
Merknad

Technical report from the  ATLAS experiment

Tilgjengelig fra: 2014-10-07 Laget: 2014-10-07 Sist oppdatert: 2014-10-09bibliografisk kontrollert
3. 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
Åpne denne publikasjonen i ny fane eller vindu >>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
Vise andre…
2014 (engelsk)Inngår i: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, nr 5, s. 1-52Artikkel i tidsskrift (Fagfellevurdert) 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.

Emneord
Supersymmetry, Hadron-Hadron Scattering
HSV kategori
Forskningsprogram
fysik
Identifikatorer
urn:nbn:se:su:diva-105872 (URN)10.1007/JHEP05(2014)071 (DOI)000336654400001 ()
Forskningsfinansiär
Swedish Research CouncilKnut and Alice Wallenberg Foundation
Merknad

AuthorCount:2886;

Tilgjengelig fra: 2014-07-08 Laget: 2014-07-07 Sist oppdatert: 2019-12-10bibliografisk kontrollert
4. Fake Isolated Muon Background in Searches for Supersymmetry with two Muons in the Final State
Åpne denne publikasjonen i ny fane eller vindu >>Fake Isolated Muon Background in Searches for Supersymmetry with two Muons in the Final State
Vise andre…
2010 (engelsk)Rapport (Annet vitenskapelig)
Abstract [en]

We study a data-driven technique to derive the contamination from fake isolated muons in a search for supersymmetric (SUSY) particles, in final states with two high pT muons. The signal sample is characterized by jets, missing transverse energy and two high pT muons, isolated from calorimeter energy. In real data, a fraction of the selected events will arise from processes where at least one of the isolated muons is not truly isolated, but rather arises in conjunction with a jet. We illustrate how to determine the contribution from fake isolated muons, to the signal sample. The method is demonstrated with a simple SUSY analysis of the di-muon sample. We study a range of potential systematic effects arising from the extrapolation from the control sample to the signal region.

Publisher
s. 34
HSV kategori
Identifikatorer
urn:nbn:se:su:diva-108052 (URN)
Merknad

Technical report from the  ATLAS experiment

Tilgjengelig fra: 2014-10-07 Laget: 2014-10-07 Sist oppdatert: 2014-10-09bibliografisk kontrollert

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Search for Weakly Produced Supersymmetric Particles in the ATLAS Experiment(3992 kB)131 nedlastinger
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