@article{OPUS4-22546,
  title     = {A search for pair-produced resonances in four-jet final states at root s=13 TeV with the ATLAS detector},
  series = {The European Physical Journal C},
  volume    = {78},
  journal   = {The European Physical Journal C},
  number    = {250},
  organization    = {The ATLAS Collaboration},
  doi       = {10.1140/epjc/s10052-018-5693-4},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-225465},
  pages     = {1-28},
  year      = {2018},
  abstract  = {A search for massive coloured resonances which are pair-produced and decay into two jets is presented. The analysis uses 36.7 fb(-1) of root s = 13 TeV pp collision data recorded by the ATLAS experiment at the LHC in 2015 and 2016. No significant deviation from the background prediction is observed. Results are interpreted in a SUSY simplified model where the lightest supersymmetric particle is the top squark, (t) over tilde, which decays promptly into two quarks through R-parity-violating couplings. Top squarks with masses in the range 100 GeV < m((T) over tilde) < 410 GeV are excluded at 95\% confidence level. If the decay is into a b-quark and a light quark, a dedicated selection requiring two b-tags is used to exclude masses in the ranges 100 GeV < m((t) over tilde) < 470 GeV and 480 GeV < m(<(t)over tilde>) < 610 GeV. Additional limits are set on the pair-production of massive colour-octet resonances.},
  language  = {en}
}
@phdthesis{Staub2010,
  author    = {Staub, Florian},
  title     = {Considerations on supersymmetric Dark Matter beyond the MSSM},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-55343},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2010},
  abstract  = {The standard model (SM) of particle physics is for the last three decades a very successful description of the properties and interactions of all known elementary particles. Currently, it is again probed with the first collisions at the Large Hadron Collider (LHC). It is widely expected that new physics will be detected at the LHC and the SM has to be extended. The most exhaustive analyzed extension of the SM is supersymmetry (SUSY). SUSY can not only solve intrinsic problems of the SM like the hierarchy problem, but it also postulates new particles which might explain the nature of dark matter in the universe. The majority of all studies about dark matter in the framework of SUSY has focused on the minimal supersymmetric standard model (MSSM). The aim of this work is to consider scenarios beyond that scope. We consider two models which explain not only dark matter but also neutrino masses: the gravitino as dark matter in gauge mediated SUSY breaking (GMSB) with bilinear broken \$R\$-parity as well as different seesaw scenarios with the neutralino as dark matter candidate. Furthermore, we also study the next-to-minimal supersymmetric standard model (NMSSM) which solves the \(\mu\)-problem of the MSSM and discuss the properties of the neutralino as dark matter candidate. In case of \$R\$-parity violation, light gravitinos are often the only remaining candidate for dark matter in SUSY because of their very long life time. We reconsider the cosmological gravitino problem arising for this kind of models. It will be shown that the proposed solution for the overclosure of the universe by light gravitinos, namely the entropy production by decays of GMSB messenger, just works in a small subset of models and in fine-tuned regions of the parameter space. This is a consequence of two effects so far overlooked: the enhanced decay channels in massive vector bosons and the impact of charged messenger particles. Both aspects cause an interplay between different cosmological restrictions which lead to strong constraints on the parameters of GMSB models. Afterwards, a minimal supergravity (mSugra) scenario with additional chiral superfields at high energy scales is considered. These fields are arranged in complete \$SU(5)\$ multiplets in order to maintain gauge unification. The new fields generate a dimension 5 operator to explain neutrino data. Furthermore, they cause large differences in mass spectrum of MSSM fields because of the different evaluation of the renormalization group equations what changes also the properties of the lightest neutralino as dark matter candidate. We discuss the parameter space of all three possible seesaw scenarios with respect to dark matter and the impact on rare lepton flavor violating processes. As we will see, especially in seesaw type~III but also in type~II the mass spectrum and regions of parameter space consistent with dark matter differ significantly in comparison to a common mSugra scenario. Moreover, the experimental bounds, in particular of branching ratios like \(l_i \rightarrow l_j \gamma\), cause large constraints on the seesaw parameters.},
  subject      = {Supersymmetrie},
  language  = {en}
}
@article{CamargoMolinaGarbrechtO'Learyetal.2014,
  author    = {Camargo-Molina, J. E. and Garbrecht, B. and O'Leary, B. and Porod, W. and Staub, F.},
  title     = {Constraining the Natural MSSM through tunneling to color-breaking vacua at zero and non-zero temperature},
  series = {Physics Letters B},
  volume    = {737},
  journal   = {Physics Letters B},
  doi       = {10.1016/j.physletb.2014.08.036},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-118458},
  pages     = {156-161},
  year      = {2014},
  abstract  = {We re-evaluate the constraints on the parameter space of the minimal supersymmetric standard model from tunneling to charge- and/or color-breaking minima, taking into account thermal corrections. We pay particular attention to the region known as the Natural MSSM, where the masses of the scalar partners of the top quarks are within an order of magnitude or so of the electroweak scale. These constraints arise from the interaction between these scalar tops and the Higgs fields, which allows the possibility of parameter points having deep charge- and color-breaking true vacua. In addition to requiring that our electroweak-symmetry-breaking, yet QCD- and electromagnetism-preserving vacuum has a sufficiently long lifetime at zero temperature, also demanding stability against thermal tunneling further restricts the allowed parameter space.},
  language  = {en}
}
@phdthesis{Kittel2004,
  author    = {Kittel, Olaf},
  title     = {CP violation in production and decay of supersymmetric particles},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-12767},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2004},
  abstract  = {In dieser Dissertation untersuchen wir CP verletzende Effekte von MSSM-Phasen in Produktion und Zwei-Teilchen-Zerfaellen von Neutralinos, Charginos und Sfermionen. Fuer verschiedene supersymmetrische Prozesse definieren und berechnen wir CP-ungerade Asymmetrien, welche auf Spatprodukten basieren. Wir zeigen numerische Ergebnisse fuer Elektron-Positron-Kollisionen an einem zukuenftigen Linearbeschleuniger mit einer Energie von 500 - 800 GeV, hoher Luminositaet und longitudinal polarisierten Strahlen.},
  subject      = {Supersymmetrisches Teilchen},
  language  = {en}
}
@phdthesis{Pahlen2005,
  author    = {Pahlen, Federico von der},
  title     = {Polarization and Spin Effects in Production and Decay of Charginos and Neutralinos at a Muon Collider},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-18421},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2005},
  abstract  = {The mechanism of spontaneous symmetry breaking is essential to provide masses to the W and Z gauge bosons and fermions of the SM. We hope to elucidate this mechanism at the next generation of colliders. While the SM has been tested with astonishing precision it is believed to be an effective theory of a more fundamental Great Unified Theory. SUSY is one of the most attractive extensions of the SM of particle physics. Therefore, the search for SUSY is a top priority at the next generation of colliders. Once Higgs bosons are discovered, a precise determination of their properties is necessary to differentiate between different models, in particular the MSSM. A muon collider, running at center of mass energies around the neutral Higgs boson resonances, would allow precise measurements of masses and widths, as well as the couplings to their decay products. In particular their couplings to supersymmetric particles are essential to probe SUSY. Therefore, we study the decays of the heavier CP-even and CP-odd Higgs bosons into lighter chargino or neutralino pairs. In this thesis we have analyzed the polarization effects of the beams and the charginos and neutralinos produced in mu+ mu- annihilation around the center of mass energies of the Higgs boson resonances H and A. For the production of equal charginos we have shown that the ratio of H-chargino and A-chargino couplings can be precisely determined independently of the chargino decay mechanism. This method avoids reference to other experiments and makes only a few model-dependent assumptions. Here we have analyzed the effect of the energy spread and of the error from the non-resonant channels, including an irreducible standard model background contribution. For small tan(beta) the process yields large cross sections of up to a pb. For the production of two different charginos we have shown that the H-A interference can be analyzed using asymmetries of the charge conjugated processes. The asymmetries depend on the muon longitudinal beam polarizations and vanish for unpolarized beams. For the chargino pair production with subsequent two-body decay of one of the charginos we have shown that charge and beam polarization asymmetries in the energy distributions of the decay particles are sensitive to the interference of scalar exchange channels with different CP quantum numbers. This process provides unique information on the interference of overlapping Higgs boson resonances. The effect is larger for regions of parameter space with intermediate values of tan(beta) and light sleptons or LSP neutralinos. For the chargino pair production with subsequent two-body decays of both charginos we have defined energy distribution and angular asymmetries in the final particles, in order to analyze the spin-spin correlations of the charginos. The transverse polarizations of the charginos are sensitive to the CP quantum number of the exchanged Higgs bosons and can thus be used to separate overlapping resonances, as well as to determine the CP quantum number of a single resonance. For equal charginos, these asymmetries are not sensitive to the interference of CP-even and CP-odd Higgs exchange channels. For the neutralino pair production in mu+ mu- annihilation we study similar processes as for chargino production. Line shape measurements of neutralino pair production allow to precisely determine the ratio of H-neutralino and A-neutralino couplings. Neutralino pair production with subsequent two-body decay of one of the neutralinos in the intermediate tan(beta) region is sensitive to the interference of H and A and may be measured with a large statistical significance. The Majorana nature of the neutralinos implies that the beam polarization asymmetries vanish for the remaining production channels. For neutralino pair production with subsequent two-body decays of both neutralinos we analyze similar observables as in chargino production. The main difference consists in the intrinsic relative CP quantum number of the neutralino pair, which depends on the chosen scenario. We have thus shown that the interaction of the Higgs bosons to the gaugino-higgsino sector can be probed at a muon collider in chargino and neutralino pair production, both analyzing the production line-shape around the resonances as well as studying the chargino and neutralino polarizations via their decays.},
  subject      = {Neutralino},
  language  = {en}
}
@article{OPUS4-22610,
  title     = {Search for new phenomena using the invariant mass distribution of same-flavour opposite-sign dilepton pairs in events with missing transverse momentum in root \(s\)=13 TeV \(pp\) collisions with the ATLAS detector},
  series = {European Physical Journal C},
  volume    = {78},
  journal   = {European Physical Journal C},
  organization    = {The ATLAS Collaboration},
  doi       = {10.1140/epjc/s10052-018-6081-9},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-226109},
  pages     = {1-38},
  year      = {2018},
  abstract  = {A search for new phenomena in final states containing an e(+)e(-) or m(+)m(-) pair, jets, and large missing transverse momentum is presented. This analysis makes use of proton-proton collision data with an integrated luminosity of 36.1 fb(-1), collected during 2015 and 2016 at a centre of-mass energy Os = 13 TeV with the ATLAS detector at the Large Hadron Collider. The search targets the pair production of supersymmetric coloured particles (squarks or gluinos) and their decays into final states containing an e(+)e(-) or m(+)m(-) pair and the lightest neutralino ((c) over tilde (0)(1)) via one of two next-to-lightest neutralino ((c) over tilde (0)(2)) decay mechanisms: (c) over tilde (0)(2) Z (c) over tilde (0)(1), where the Z boson decays leptonically leading to a peak in the dilepton invariant mass distribution around the Z boson mass; and (c) over tilde (0)(2) l(+)1(-) (c) over tilde (0)(1) with no intermediate l(+)l(-) resonance, yielding a kinematic endpoint in the dilepton invariant mass spectrum. The data are found to be consistent with the Standard Model expectation. Results are interpreted using simplified models, and exclude gluinos and squarks with masses as large as 1.85 and 1.3 TeV at 95\% confidence level, respectively.},
  language  = {en}
}
@article{OPUS4-17230,
  title     = {Search for new phenomena with large jet multiplicities and missing transverse momentum using large-radius jets and flavour-tagging at ATLAS in 13 TeV \(pp\) collisions},
  series = {Journal of High Energy Physics},
  volume    = {34},
  journal   = {Journal of High Energy Physics},
  organization    = {The ATLAS Collaboration},
  doi       = {10.1007/JHEP12(2017)034},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-172302},
  year      = {2017},
  abstract  = {A search is presented for particles that decay producing a large jet multiplicity and invisible particles. The event selection applies a veto on the presence of isolated electrons or muons and additional requirements on the number of \(b\)-tagged jets and the scalar sum of masses of large-radius jets. Having explored the full ATLAS 2015-2016 dataset of LHC proton-proton collisions at \(\sqrt{s}\) = 13 TeV, which corresponds to 36.1 fb\(^{-1}\) of integrated luminosity, no evidence is found for physics beyond the Standard Model. The results are interpreted in the context of simplified models inspired by R-parity-conserving and R-parity-violating supersymmetry, where gluinos are pair-produced. More generic models within the phenomenological minimal supersymmetric Standard Model are also considered.},
  language  = {en}
}
@article{OPUS4-22601,
  title     = {Search for pair production of Higgsinos in final states with at least three \(b\)-tagged jets in root \(s\)=13 TeV \(pp\) collisions using the ATLAS detector},
  series = {Physical Review D},
  volume    = {98},
  journal   = {Physical Review D},
  organization    = {The ATLAS Collaboration},
  doi       = {10.1103/PhysRevD.98.092002},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-226010},
  pages     = {1-34},
  year      = {2018},
  abstract  = {A search for pair production of the supersymmetric partners of the Higgs boson (higgsinos (H) over tilde) in gaugemediated scenarios is reported. Each higgsino is assumed to decay to a Higgs boson and a gravitino. Two complementary analyses, targeting high- and low-mass signals, are performed to maximize sensitivity. The two analyses utilize LHC pp collision data at a center-of-mass energy root s = 13 TeV, the former with an integrated luminosity of 36.1 fb(-1) and the latter with 24.3 fb(-1), collected with the ATLAS detector in 2015 and 2016. The search is performed in events containing missing transverse momentum and several energetic jets, at least three of which must be identified as b-quark jets. No significant excess is found above the predicted background. Limits on the cross section are set as a function of the mass of the <(Hover tilde> in simplified models assuming production via mass-degenerate higgsinos decaying to a Higgs boson and a gravitino. Higgsinos with masses between 130 and 230 GeV and between 290 and 880 GeV are excluded at the 95\% confidence level. Interpretations of the limits in terms of the branching ratio of the higgsino to a Z boson or a Higgs boson are also presented, and a 45\% branching ratio to a Higgs boson is excluded for m(<(Hover tilde>) approximate to 400 GeV.},
  language  = {en}
}
@article{OPUS4-27753,
  title     = {Search for squarks and gluinos in final states with same-sign leptons and jets using 139 fb\(^{-1}\) of data collected with the ATLAS detector},
  series = {Journal of High Energy Physics},
  journal   = {Journal of High Energy Physics},
  number    = {6},
  organization    = {The ATLAS Collaboration},
  doi       = {10.1007/JHEP06(2020)046},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-277538},
  pages     = {46},
  year      = {2020},
  abstract  = {A search for supersymmetric partners of gluons and quarks is presented, involving signatures with jets and either two isolated leptons (electrons or muons) with the same electric charge, or at least three isolated leptons. A data sample of proton-proton collisions at root s = 13 TeV recorded with the ATLAS detector at the Large Hadron Collider between 2015 and 2018, corresponding to a total integrated luminosity of 139 fb(-1), is used for the search. No significant excess over the Standard Model expectation is observed. The results are interpreted in simplified supersymmetric models featuring both R-parity conservation and R-parity violation, raising the exclusion limits beyond those of previous ATLAS searches to 1600 GeV for gluino masses and 750 GeV for bottom and top squark masses in these scenarios.},
  language  = {en}
}
@phdthesis{Schreyer2015,
  author    = {Schreyer, Manuel},
  title     = {Search for supersymmetry in events containing light leptons, jets and missing transverse momentum in \(\sqrt{s}\) = 8 TeV pp collisions with the ATLAS detector},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-120863},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2015},
  abstract  = {The results of two analyses searching for supersymmetry (SUSY) in data of the ATLAS experiment are presented in this thesis. The data were recorded in proton-proton collisions at the Large Hadron Collider in 2012 at a centre of mass energy of \(\sqrt{s}\)=8 TeV and correspond to an integrated luminosity of 20.3 fb\(^{-1}\). The first search is performed in signatures containing an opposite-sign electron or muon pair, which is compatible with originating from a Z boson decay, in addition to jets and large missing transverse momentum. The analysis targets the production of squarks and gluinos in R-parity conserving (RPC) models with SUSY breaking via General Gauge Mediation (GGM). The main Standard Model (SM) backgrounds are \(t\overline t\), WW, W+t and Z to \(\tau \tau\) processes which are entirely estimated from data using different-flavour events. Besides that, the SM production of Z bosons in association with jets and large fake missing momentum from mismeasurements plays a role and is predicted with the data-driven jet smearing method. Backgrounds from events with fake leptons are estimated with the data-driven matrix method. WZ/ZZ production as well as smaller background contributions are determined from Monte-Carlo simulations. The search observes an excess of data over the SM prediction with a local significance of 3.0 \(\sigma\) in the electron channel, 1.7 \(\sigma\) in the muon channel and 3.0 \(\sigma\) when the two channels are added together. The results are used to constrain the parameters of the GGM model. The second analysis uses the already published results of an ATLAS search for SUSY in events with one isolated electron or muon, jets and missing transverse momentum to reinterpret them in the context of squark and gluino production in SUSY models with R-parity violating (RPV) \(LQ\overline D\)-operators. In contrast to RPC models, the lightest SUSY particle (LSP) is not stable but decays into SM particles. "Standard" analyses often do not consider SUSY models with RPV although they are in principle sensitive to them. The exclusion limits on the squark and gluino mass obtained from the reinterpretation extend up to 1200 GeV. These are the first results by any ATLAS SUSY search which systematically cover a wide range of RPV couplings in the case of prompt LSP decays. However, the analysis is not sensitive to the full parameter space of the \(LQ\overline D\)-model and reveals gaps in the ATLAS SUSY program which have to be closed by dedicated search strategies in the future.},
  subject      = {Supersymmetrie},
  language  = {en}
}