@article{AadAbbottAbdallahetal.2012, author = {Aad, G. and Abbott, B. and Abdallah, J. and Abdel Khalek, S. and Abdelalim, A. A.}, title = {Search for the Standard Model Higgs boson in the H→WW(⋆)→ℓνℓνH→WW(⋆)→ℓνℓν decay mode with 4.7 fb\(^{-1}\) of ATLAS data at \(\sqrt{s}\)=7 TeV}, series = {Physics Letters B}, volume = {761}, journal = {Physics Letters B}, number = {1}, organization = {ATLAS Collaboration}, doi = {10.1016/j.physletb.2012.08.010}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-127307}, pages = {62-81}, year = {2012}, abstract = {A search for the Standard Model Higgs boson in the H→WW(⋆)→ℓνℓνH→WW(⋆)→ℓνℓν (ℓ=e,μℓ=e,μ) decay mode is presented. The search is performed using proton-proton collision data corresponding to an integrated luminosity of 4.7 fb\(^{-1}\) at a centre-of-mass energy of 7 TeV collected during 2011 with the ATLAS detector at the Large Hadron Collider. No significant excess of events over the expected background is observed. An upper bound is placed on the Higgs boson production cross section as a function of its mass. A Standard Model Higgs boson with mass in the range between 133 GeV and 261 GeV is excluded at 95\% confidence level, while the expected exclusion range is from 127 GeV to 233 GeV.}, language = {en} } @article{AadAbbottAbdallahetal.2012, author = {Aad, G. and Abbott, B. and Abdallah, J. and Abdelalim, A. A. and Abdesselam, A.}, title = {Performance of the ATLAS Trigger System in 2010}, series = {The European Physical Journal C}, volume = {72}, journal = {The European Physical Journal C}, number = {1849}, doi = {10.1140/epjc/s10052-011-1849-1}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-127321}, year = {2012}, abstract = {Proton-proton collisions at √s=7 TeV and heavy ion collisions at \(\sqrt{sNN}\)=2.76 TeV were produced by the LHC and recorded using the ATLAS experiment's trigger system in 2010. The LHC is designed with a maximum bunch crossing rate of 40 MHz and the ATLAS trigger system is designed to record approximately 200 of these per second. The trigger system selects events by rapidly identifying signatures of muon, electron, photon, tau lepton, jet, and B meson candidates, as well as using global event signatures, such as missing transverse energy. An overview of the ATLAS trigger system, the evolution of the system during 2010 and the performance of the trigger system components and selections based on the 2010 collision data are shown. A brief outline of plans for the trigger system in 2011 is presented.}, language = {en} } @phdthesis{Meyer2012, author = {Meyer, Jochen}, title = {Muon performance aspects and measurement of the inclusive ZZ production cross section through the four lepton final state with the ATLAS experiment at the LHC}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-78793}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2012}, abstract = {The "Large Hadron Collider" (LHC) is currently the most powerful particle accelerator. It provides particle collisions at a center of mass energy in the Tera-electronvolt range, which had never been reached in a laboratory before. Thereby a new era in high energy particle physics has began. Now it is possible to test one of the most precise theories in physics, the Standard Model of particle physics, at these high energies. The purpose is particularly served by four large experiments installed at the LHC, namely "A Toroidal LHC ApparatuS" (ATLAS), the "Compact-Muon-Solenoid" (CMS), the "Large Hadron Collider beauty" (LHCb) and "A Large Ion Collider Experiment" (ALICE). Besides exploring the high energy behavior of the well-established portions of the Standard Model, one of the main objectives is to find the Higgs boson included in the model, but not discovered by any preceding effort. It is of tremendous importance since fermions and heavy electroweak gauge bosons acquire mass because of this boson. Although the success of the Standard Model in describing nature is already undisputed, there are some flaws due to observations inexplicable within this theory only. Therefore searches for physics beyond the Standard Model are promoted at the LHC experiments as well. In order to achieve the defined goals, crucial aspects are firstly precise measurements, to verify Standard Model predictions in detail, and secondly an evaluation of as much information as accessible by the detectors, to recognize new phenomena as soon as possible for subsequent optimizations. Both challenges are only possible with a superior understanding of the detectors. An inevitable contribution to attain this knowledge is a realistic simulation, partially requiring new implementation techniques to describe the very complex instrumentation. The research presented here is performed under the patronage of the ATLAS collaboration with a special focus on measurements done with muon spectrometer. Thus a first central issue is the performance of the spectrometer in terms of physics objects that are recognized by the device, the compatibility of data and the existing simulation as well as its improvement and finally the extension of the acceptance region. Once the excellent behavior and comprehension of the muon spectrometer is demonstrated, a second part addresses one physics use case of reconstructed muons. The electroweak force is part of the Standard Model and causes the interaction of heavy electroweak gauge bosons with fermions as well as their self-interaction. In proton-proton collisions such gauge bosons are produced. However, they decay immediately into a pair of fermions. In case of the Z boson, which is one of the gauge bosons, oppositely charged fermions of the same generation, including muons, emerge. The various decay modes are determined precisely at particle accelerators other than the LHC. However, the associated production of two Z bosons is measured less exactly at those facilities because of a very low cross section. The corresponding results acquired with the ATLAS experiment exceed all previous measurements in terms of statistics and accuracy. They are reported in this thesis as obtained from the observation of events with four charged leptons. The enhancement of the signal yield based on the extension of the muon spectrometer acceptance is especially emphasized as well as alternative methods to estimate background events. Furthermore, the impact on the probing of couplings of three Z bosons and intersection with the search for the Standard Model Higgs boson are pointed out.}, subject = {ATLAS }, language = {en} } @article{OPUS4-12785, title = {Search for anomaly-mediated supersymmetry breaking with the ATLAS detector based on a disappearing-track signature in pp collisions at √s=7 TeV}, series = {The European Physical Journal C}, volume = {72}, journal = {The European Physical Journal C}, number = {1993}, organization = {ATLAS Collaboration}, doi = {10.1140/epjc/s10052-012-1993-2}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-127850}, year = {2012}, abstract = {In models of anomaly-mediated supersymmetry breaking (AMSB), the lightest chargino is predicted to have a lifetime long enough to be detected in collider experiments. This letter explores AMSB scenarios in pp collisions at √s=7 TeV by attempting to identify decaying charginos which result in tracks that appear to have few associated hits in the outer region of the tracking system. The search was based on data corresponding to an integrated luminosity of 1.02 fb\(^{-1}\) collected with the ATLAS detector in 2011. The p\(_T\) spectrum of candidate tracks is found to be consistent with the expectation from Standard Model background processes and constraints on the lifetime and the production cross section were obtained. In the minimal AMSB framework with m\(_{3/2}\)<32 TeV, m\(_0\)<1.5 TeV, tanβ=5 and μ>0, a chargino having mass below 92 GeV and a lifetime between 0.5 ns and 2 ns is excluded at 95 \% confidence level.}, language = {en} } @article{OPUS4-12796, title = {Measurement of W\(^{±}\)Z production in proton-proton collisions at √s=7 TeV with the ATLAS detector}, series = {European Physical Journal C}, volume = {72}, journal = {European Physical Journal C}, number = {2173}, organization = {ATLAS Collaboration}, doi = {10.1140/epjc/s10052-012-2173-0}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-127963}, year = {2012}, abstract = {A study of W\(^{±}\)Z production in proton-proton collisions at √s=7 TeV is presented using data corresponding to an integrated luminosity of 4.6 fb\(^{-1}\) collected with the ATLAS detector at the Large Hadron Collider in 2011. In total, 317 candidates, with a background expectation of 68±10 events, are observed in double-leptonic decay final states with electrons, muons and missing transverse momentum. The total cross-section is determined to be σ\(^{tot}_{WZ}\)=19.0\(^{+1.4}_{-1.3}\)(stat.)±0.9(syst.)±0.4(lumi.) pb, consistent with the Standard Model expectation of 17.6\(^{+1.1}_{-1.0}\) pb. Limits on anomalous triple gauge boson couplings are derived using the transverse momentum spectrum of Z bosons in the selected events. The cross-section is also presented as a function of Z boson transverse momentum and diboson invariant mass.}, language = {en} } @article{OPUS4-13986, title = {Search for s-channel single top-quark production in proton-proton collisions at \(\sqrt{s}\)=8 TeV with the ATLAS detector}, series = {Physics Letters B}, volume = {740}, journal = {Physics Letters B}, organization = {ATLAS Collaboration}, doi = {10.1016/j.physletb.2014.11.042}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-139869}, pages = {118-136}, year = {2015}, abstract = {This Letter presents a search at the LHC for s-channel single top-quark production in proton-proton collisions at a centre-of-mass energy of 8 TeV. The analyzed data set was recorded by the ATLAS detector and corresponds to an integrated luminosity of 20.3 fb\(^{-1}\). Selected events contain one charged lepton, large missing transverse momentum and exactly two b-tagged jets. A multivariate event classifier based on boosted decision trees is developed to discriminate s-channel single top-quark events from the main background contributions. The signal extraction is based on a binned maximum-likelihood fit of the output classifier distribution. The analysis leads to an upper limit on the s-channel single top-quark production cross-section of 14.6 pb at the 95\% confidence level. The fit gives a cross-section of σs=5.0±4.3 pb, consistent with the Standard Model expectation.}, language = {en} } @article{OPUS4-14990, title = {Measurement of the top-quark mass in the fully hadronic decay channel from ATLAS data at \(\sqrt {s}\)=7TeV}, series = {European Physical Journal C: Particles and Fields}, volume = {75}, journal = {European Physical Journal C: Particles and Fields}, number = {4}, organization = {ATLAS Collaboration}, doi = {10.1140/epjc/s10052-015-3373-1}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-149905}, pages = {158}, year = {2015}, abstract = {The mass of the top quark is measured in a data set corresponding to 4.6  fb\(^{-1}\) of proton-proton collisions with centre-of-mass energy \(\sqrt {s}\)=7 TeV collected by the ATLAS detector at the LHC. Events consistent with hadronic decays of top-antitop quark pairs with at least six jets in the final state are selected. The substantial background from multijet production is modelled with data-driven methods that utilise the number of identified b-quark jets and the transverse momentum of the sixth leading jet, which have minimal correlation. The top-quark mass is obtained from template fits to the ratio of three-jet to dijet mass. The three-jet mass is calculated from the three jets produced in a top-quark decay. Using these three jets the dijet mass is obtained from the two jets produced in the W boson decay. The top-quark mass obtained from this fit is thus less sensitive to the uncertainty in the energy measurement of the jets. A binned likelihood fit yields a top-quark mass of m\(_{t}\)= 175.1 ± 1.4 (stat.) ± 1.2 (syst.) GeV.}, language = {en} } @article{OPUS4-14305, title = {Search for a CP-odd Higgs boson decaying to Zh in pp collisions at \(\sqrt{s}\)=8 TeV with the ATLAS detector}, series = {Physics Letters B}, volume = {744}, journal = {Physics Letters B}, organization = {ATLAS Collaboration}, doi = {10.1016/j.physletb.2015.03.054}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-143050}, pages = {163-183}, year = {2015}, abstract = {A search for a heavy, CP-odd Higgs boson, A, decaying into a Z boson and a 125 GeV Higgs boson, h, with the ATLAS detector at the LHC is presented. The search uses proton-proton collision data at a centre-of-mass energy of 8 TeV corresponding to an integrated luminosity of 20.3 fb\(^{-1}\). Decays of CP-even h bosons to ττ or bb pairs with the Z boson decaying to electron or muon pairs are considered, as well as h→bb decays with the Z boson decaying to neutrinos. No evidence for the production of an A boson in these channels is found and the 95\% confidence level upper limits derived for σ(gg→A)×BR(A→Zh)×BR(h→f\(\bar{f}\)) are 0.098-0.013 pb for f=τ and 0.57-0.014 pb for f=b in a range of m\(_{A}\)=220-1000 GeVmA=220-1000 GeV. The results are combined and interpreted in the context of two-Higgs-doublet models.}, language = {en} }