@article{OPUS4-17246, title = {Search for new high-mass phenomena in the dilepton final state using 36 fb\(^{-1}\) of proton-proton collision data at \(\sqrt{s}=13\) TeV with the ATLAS detector}, series = {Journal of High Energy Physics}, volume = {2017}, journal = {Journal of High Energy Physics}, number = {182}, organization = {The ATLAS Collaboration}, doi = {10.1007/JHEP10(2017)182}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-172462}, year = {2017}, abstract = {A search is conducted for new resonant and non-resonant high-mass phenomena in dielectron and dimuon final states. The search uses 36.1 fb\(^{-1}\) of proton-proton collision data, collected at \(\sqrt{s}=13\) TeV by the ATLAS experiment at the LHC in 2015 and 2016. No significant deviation from the Standard Model prediction is observed. Upper limits at 95\% credibility level are set on the cross-section times branching ratio for resonances decaying into dileptons, which are converted to lower limits on the resonance mass, up to 4.1 TeV for the E\(_6\)-motivated \(Z^′_χ\). Lower limits on the \({qqℓℓ}\) contact interaction scale are set between 2.4 TeV and 40 TeV, depending on the model.}, language = {en} } @article{OPUS4-17321, title = {Search for direct top squark pair production in events with a Higgs or \(Z\) boson, and missing transverse momentum in \(\sqrt{s}\) = 13 TeV \(pp\) collisions with the ATLAS detector}, series = {Journal of High Energy Physics}, volume = {2017}, journal = {Journal of High Energy Physics}, number = {08}, organization = {The ATLAS Collaboration}, doi = {https://doi.org/10.1007/JHEP08(2017)006}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-173210}, year = {2017}, abstract = {A search for direct top squark pair production resulting in events with either a same-flavour opposite-sign dilepton pair with invariant mass compatible with a \(Z\) boson or a pair of jets compatible with a Standard Model (SM) Higgs boson (\(h\)) is presented. Requirements on the missing transverse momentum, together with additional selections on leptons, jets, jets identified as originating from \(b\)-quarks are imposed to target the other decay products of the top squark pair. The analysis is performed using proton-proton collision data at \(\sqrt{s}\) = 13 TeV collected with the ATLAS detector at the LHC in 2015-2016, corresponding to an integrated luminosity of 36.1 fb\(^{-1}\). No excess is observed in the data with respect to the SM predictions. The results are interpreted in two sets of models. In the first set, direct production of pairs of lighter top squarks (\(\tilde{t}_1\)) with long decay chains involving \(Z\) or Higgs bosons is considered. The second set includes direct pair production of the heavier top squark pairs (\(\tilde{t}_2\)) decaying via \(\tilde{t}_2\) → \(Z\tilde{t}_1\) or \(\tilde{t}_2\) → \(h\tilde{t}_1\). The results exclude at 95\% confidence level \(\tilde{t}_2\) and \(\tilde{t}_1\) masses up to about 800 GeV, extending the exclusion region of supersymmetric parameter space covered by previous LHC searches.}, 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{OPUS4-17280, title = {Search for new phenomena in a lepton plus high jet multiplicity final state with the ATLAS experiment using \(\sqrt{s}=13\) TeV proton-proton collision data}, series = {Journal of High Energy Physics}, volume = {2017}, journal = {Journal of High Energy Physics}, number = {09}, organization = {The ATLAS Collaboration}, doi = {https://doi.org/10.1007/JHEP09(2017)088}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-172802}, year = {2017}, abstract = {A search for new phenomena in final states characterized by high jet multiplicity, an isolated lepton (electron or muon) and either zero or at least three \(b\)-tagged jets is presented. The search uses 36.1 fb\(^{-1}\) of \(\sqrt{s}=13\) TeV proton-proton collision data collected by the ATLAS experiment at the Large Hadron Collider in 2015 and 2016. The dominant sources of background are estimated using parameterized extrapolations, based on observables at medium jet multiplicity, to predict the \(b\)-tagged jet multiplicity distribution at the higher jet multiplicities used in the search. No significant excess over the Standard Model expectation is observed and 95\% confidence-level limits are extracted constraining four simplified models of \(R\)-parity-violating supersymmetry that feature either gluino or top-squark pair production. The exclusion limits reach as high as 2.1 TeV in gluino mass and 1.2 TeV in top-squark mass in the models considered. In addition, an upper limit is set on the cross-section for Standard Model \(t\overline{t}t\overline{t}\) production of 60 fb (6.5 × the Standard Model prediction) at 95\% confidence level. Finally, model-independent limits are set on the contribution from new phenomena to the signal-region yields.}, language = {en} }