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Search for same-sign dilepton signatures with the ATLAS detector

Helgadóttir, Inga Rún LU (2014) FYSM60 20132
Department of Physics
Particle and nuclear physics
Abstract
This thesis presents the work I did for the inclusive search for anomalous production
of same charge lepton-pairs, originating from the collision point, at sqrt(s) = 8 TeV with the ATLAS detector at the LHC using the 2012 data. I optimized the selection criteria for isolated electrons and muons, calculated the so-called "fake factors" and "fake factor" systematic uncertainties for the muon selection. The fake-factor is used to estimate the contribution in the region of interest due to muons coming from secondary vertices, i.e. background muons. Furthermore I extracted limits of the cross-section of new sources of isolated, same-sign leptons originating from the collision point. The isolation criteria and the limits are used in the paper... (More)
This thesis presents the work I did for the inclusive search for anomalous production
of same charge lepton-pairs, originating from the collision point, at sqrt(s) = 8 TeV with the ATLAS detector at the LHC using the 2012 data. I optimized the selection criteria for isolated electrons and muons, calculated the so-called "fake factors" and "fake factor" systematic uncertainties for the muon selection. The fake-factor is used to estimate the contribution in the region of interest due to muons coming from secondary vertices, i.e. background muons. Furthermore I extracted limits of the cross-section of new sources of isolated, same-sign leptons originating from the collision point. The isolation criteria and the limits are used in the paper on the search for anomalous production of same-sign lepton-pairs originating from the collision point, which will be published soon.
I found that for this analysis the best background rejection while still achieving a good signal efficiency is accomplished by using isolation criteria based on both calorimeter and tracking information.
The muon fake factors are calculated in a data-driven way using muon pairs having the
same charge. The fake factors obtained using the new selection criteria for isolated muon tracks are higher than when the isolation criteria from the previous analysis is used, but the new criteria also accepts substantially more true same-sign muons originating from the collision point, resulting in a lower ratio of muons originating from secondary vertices to muons originating from the collision point in the region of interest.
As we are working on publishing the results it was not possible to analyse the region
of interest because of internal ATLAS restrictions. Hence it is not known whether the
data agrees with the predictions from known physics processes. If no excess is found in the number of lepton pairs I will put limits on the cross section of new resonances. At the moment I am only allowed to calculate the expected limits. (Less)
Please use this url to cite or link to this publication:
author
Helgadóttir, Inga Rún LU
supervisor
organization
course
FYSM60 20132
year
type
H2 - Master's Degree (Two Years)
subject
language
English
id
4311433
date added to LUP
2014-02-24 17:58:49
date last changed
2014-10-22 10:20:07
@misc{4311433,
  abstract     = {{This thesis presents the work I did for the inclusive search for anomalous production
of same charge lepton-pairs, originating from the collision point, at sqrt(s) = 8 TeV with the ATLAS detector at the LHC using the 2012 data. I optimized the selection criteria for isolated electrons and muons, calculated the so-called "fake factors" and "fake factor" systematic uncertainties for the muon selection. The fake-factor is used to estimate the contribution in the region of interest due to muons coming from secondary vertices, i.e. background muons. Furthermore I extracted limits of the cross-section of new sources of isolated, same-sign leptons originating from the collision point. The isolation criteria and the limits are used in the paper on the search for anomalous production of same-sign lepton-pairs originating from the collision point, which will be published soon.
I found that for this analysis the best background rejection while still achieving a good signal efficiency is accomplished by using isolation criteria based on both calorimeter and tracking information.
The muon fake factors are calculated in a data-driven way using muon pairs having the
same charge. The fake factors obtained using the new selection criteria for isolated muon tracks are higher than when the isolation criteria from the previous analysis is used, but the new criteria also accepts substantially more true same-sign muons originating from the collision point, resulting in a lower ratio of muons originating from secondary vertices to muons originating from the collision point in the region of interest.
As we are working on publishing the results it was not possible to analyse the region
of interest because of internal ATLAS restrictions. Hence it is not known whether the
data agrees with the predictions from known physics processes. If no excess is found in the number of lepton pairs I will put limits on the cross section of new resonances. At the moment I am only allowed to calculate the expected limits.}},
  author       = {{Helgadóttir, Inga Rún}},
  language     = {{eng}},
  note         = {{Student Paper}},
  title        = {{Search for same-sign dilepton signatures with the ATLAS detector}},
  year         = {{2014}},
}