833 research outputs found

    Interpretations of SUSY Searches in ATLAS with Simplified Models

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    We present the status of interpretations of Supersymmetry (SUSY) searches in ATLAS at the Large Hadron Collider (LHC) using simplified models. Such models allow a systematic scan through the phase space in the sparticle mass plane, and in the corresponding final state kinematics. Models at various levels of simplification have been studied in ATLAS. The results can be extrapolated to more general new physics models which lead to the same event topology with similar mass hierarchies. Searches in the no-lepton channel with 1.04 fb^-1 of data from 2011 and the same-sign dilepton channel with 35 pb^-1 of data from 2010 are presented. No excess above the Standard Model expectation is observed, and the results are interpreted using the simplified models.Comment: 9 pages, 7 figures, 3 tables, for the proceedings of the DPF-2011 conference, Providence, RI, August 9-13, 201

    Effect of biopsy on survival of melanoma patients

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    Background Cutaneous malignant melanoma has a poor prognosis. The detrimental effect of incisional biopsies on the outcome of malignant melanoma has been debated. The aim of this study was to determine the effect of the presence and type of biopsy on the prognosis of malignant melanoma. Methods The medical records of 109 malignant melanoma patients treated at Tokushima University Hospital from 1983 to 2007 were reviewed. After excluding 28 cases with stage 0 disease or incomplete data, 81 cases were analyzed in detail with respect to patient sex, age, tumor site, clinical stage at diagnosis, presence of ulceration or lymph node metastasis, and prognosis. The five-year survival and five-year disease-free survival rates of patients who underwent incisional or excisional biopsies were compared with those who did not undergo a biopsy. Results The male-to-female ratio was 1:1.19. The mean age was 61.3 years (range, 19–93 years). The most common site was a lower extremity, and the most common clinical stage was stage II. No significant differences in clinicopathological features, five-year survival rates, and five-year disease-free survival rates were observed among the three groups. Conclusions The presence and type of biopsy neither affected the metastatic rate nor the prognosis of malignant melanoma. The use of incisional biopsies is not encouraged because tumor thickness cannot be measured accurately. However, they may be helpful for confirming the diagnosis if an excisional biopsy cannot be performed

    Extended Symmetry Preserving Attention Networks for LHC Analysis

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    Reconstructing unstable heavy particles requires sophisticated techniques to sift through the large number of possible permutations for assignment of detector objects to partons. An approach based on a generalized attention mechanism, symmetry preserving attention networks (SPANet), has been previously applied to top quark pair decays at the Large Hadron Collider, which produce six hadronic jets. Here we extend the SPANet architecture to consider multiple input streams, such as leptons, as well as global event features, such as the missing transverse momentum. In addition, we provide regression and classification outputs to supplement the parton assignment. We explore the performance of the extended capability of SPANet in the context of semi-leptonic decays of top quark pairs as well as top quark pairs produced in association with a Higgs boson. We find significant improvements in the power of three representative studies: search for ttH, measurement of the top quark mass and a search for a heavy Z' decaying to top quark pairs. We present ablation studies to provide insight on what the network has learned in each case

    Search for top-quark decays t → Hq with 36 fb−1 of pp collision data at √ s= 13 TeV with the ATLAS detector

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    A search for flavour-changing neutral current decays of a top quark into an up-type quark (q = u, c) and the Standard Model Higgs boson, t → Hq, is presented. The search is based on a dataset of pp collisions at s√ = 13 TeV recorded in 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider and corresponding to an integrated luminosity of 36.1 fb−1. Two complementary analyses are performed to search for top-quark pair events in which one top quark decays into Wb and the other top quark decays into Hq, and target the H→bb¯¯ and H → τ+τ− decay modes, respectively. The high multiplicity of b-quark jets, or the presence of hadronically decaying τ-leptons, is exploited in the two analyses respectively. Multivariate techniques are used to separate the signal from the background, which is dominated by top-quark pair production. No significant excess of events above the background expectation is found, and 95% CL upper limits on the t → Hq branching ratios are derived. The combination of these searches with ATLAS searches in diphoton and multilepton final states yields observed (expected) 95% CL upper limits on the t → Hc and t → Hu branching ratios of 1.1 × 10−3 (8.3 × 10−4) and 1.2 × 10−3 (8.3 × 10−4), respectively. The corresponding combined observed (expected) upper limits on the |λtcH| and |λtuH| couplings are 0.064 (0.055) and 0.066 (0.055), respectively

    Erratum to: Measurement of the W boson polarisation in tt¯ events from pp collisions at √s=8 TeV in the lepton + jets channel with ATLAS

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    This paper presents a measurement of the polarisation of W bosons from tt¯ decays, reconstructed in events with one high-p T lepton and at least four jets. Data from pp collisions at the LHC were collected at s√ = 8 TeV and correspond to an integrated luminosity of 20.2 fb−1. The angle θ∗ between the b-quark from the top quark decay and a direct W boson decay product in the W boson rest frame is sensitive to the W boson polarisation. Two different W decay products are used as polarisation analysers: the charged lepton and the down-type quark for the leptonically and hadronically decaying W boson, respectively. The most precise measurement of the W boson polarisation via the distribution of cosθ∗ is obtained using the leptonic analyser and events in which at least two of the jets are tagged as b-quark jets. The fitted fractions of longitudinal, left- and right-handed polarisation states are F0= 0.709 ± 0.019, FL= 0.299 ± 0.015 and FR= −0.008 ± 0.014, and are the most precisely measured W boson polarisation fractions to date. Limits on anomalous couplings of the Wtb vertex are set.The original article can be found online at https://doi.org/10.1140/epjc/s10052-017-4819-4

    Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

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    A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements

    Why Are Outcomes Different for Registry Patients Enrolled Prospectively and Retrospectively? Insights from the Global Anticoagulant Registry in the FIELD-Atrial Fibrillation (GARFIELD-AF).