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Identification of Pile-up Using the Quality Factor of Pulse Shapes in the ATLAS Tile Calorimeter
Stockholm University, Faculty of Science, Department of Physics. (Elementary Particle Physics)
Stockholm University, Faculty of Science, Department of Physics. (Elementary Particle Physics)ORCID iD: 0000-0003-1661-6873
2012 (English)Report (Other academic)
Abstract [en]

The ATLAS experiment records data from the proton-proton collisions produced by the Large Hadron Collider (LHC). The Tile Calorimeter is the hadronic sampling calorimeter of ATLAS in the region |η|<1.7. It uses iron absorbers and scintillators as active material. The LHC will provide collisions every 25 ns, putting very strong requirements on the energy measurement in presence of energy deposits from different collisions in the same read out window and physical calorimeter channel (pile-up). In 2011 the LHC was running with filled bunches at 50 ns spacing and at intensities which yield up to about 8 proton-proton collisions per bunch crossing. We present a quality factor that is computed offline for each collision and for each calorimeter channel, and provide criteria to detect pile-up in TileCal channels. The quality factor can be used to select channels that need a special treatment to account for large energy deposition from pile-up.

Place, publisher, year, edition, pages
2012. , 25 p.
National Category
Subatomic Physics
Research subject
Physics
Identifiers
URN: urn:nbn:se:su:diva-120016OAI: oai:DiVA.org:su-120016DiVA: diva2:850100
Note

Technical report from the ATLAS experiment

Available from: 2015-08-31 Created: 2015-08-31 Last updated: 2015-09-02Bibliographically approved
In thesis
1. 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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