633 research outputs found

    Measurements of the ttˉH(bbˉ)\text{t}\bar{\text{t}}\text{H}(\text{b}\bar{\text{b}}) Process with Neural Networks at the CMS Experiment - Current Status and Future Prospects

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    This thesis presents a measurement of the production of a Standard Model Higgs boson in association with a top quark-antiquark pair (ttˉH\text{t}\bar{\text{t}}\text{H}), where the Higgs boson in candidate ttˉH\text{t}\bar{\text{t}}\text{H} events is required to decay into a bottom quark-antiquark pair (ttˉH(bbˉ)\text{t}\bar{\text{t}}\text{H}(\text{b}\bar{\text{b}})). The results are based on data recorded at the CMS experiment in the years from 2016 to 2018, corresponding to an integrated luminosity of 137.5 fb−1\,\text{fb}^{-1}. In particular, the semileptonic decay mode of the ttˉ\text{t}\bar{\text{t}} system is discussed. The strategy for the discrimination of signal and background events is based on the multiplicity of b-tagged jets and an event categorization performed by feed-forward neural networks. The compatibility of the statistical model used for the measurement and the observed data is evaluated using different statistical tests, which indicate good agreement. At the time of writing this thesis, final tests for the estimation of the signal strength for the ttˉH(bbˉ)\text{t}\bar{\text{t}}\text{H}(\text{b}\bar{\text{b}}) process with respect to the Standard Model prediction ÎŒ=σobs/σSM\mu = \sigma^\text{obs}/\sigma^\text{SM} are performed. Therefore, the sensitivity expected within the scope of the Standard Model prediction is discussed, which corresponds to an expected significance of 3.3 3.3\,standard deviations with respect to the background-only hypothesis in the semileptonic channel. Additionally, the impact of the semileptonic analysis on the results obtained in a combined parameter estimation with analyses targeting the other ttˉ\text{t}\bar{\text{t}} decay modes is discussed. Moreover, the results are reinterpreted in the scope of the Simplified Template Cross Section (STXS) measurement, where the cross sections in five regions of the transverse momentum of the Higgs boson are estimated simultaneously. The expected results from the STXS interpretation are used to conduct first feasibility studies of measurements of effects beyond the Standard Model as described in the Standard Model Effective Field Theory for the ttˉH(bbˉ)\text{t}\bar{\text{t}}\text{H}(\text{b}\bar{\text{b}}) process within the CMS experiment. Finally, the sensitivity for ttˉH(bbˉ)\text{t}\bar{\text{t}}\text{H}(\text{b}\bar{\text{b}}) measurements with future data sets is discussed, which is expected to reach approximately 7 %7\,\% with the estimated amount of data collected by the end of the High Luminosity LHC

    Machine Learning in Top Physics in the ATLAS and CMS Collaborations

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    Machine learning is essential in many aspects of top-quark related physics in the ATLAS and CMS Collaborations. This work aims to give a brief overview over current applications in the two collaborations as well as on-going studies for future applications. Copyright 2023 CERN for the benefit of the ATLAS and CMS Collaborations. Reproduction of this article or parts of it is allowed as specified in the CC-BY-4.0 licenseComment: Talk at the 15th International Workshop on Top Quark Physics, Durham, UK, 4-9 September 202

    Combined searches for the production of supersymmetric top quark partners in proton-proton collisions at root s=13 TeV

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    A combination of searches for top squark pair production using proton-proton collision data at a center-of-mass energy of 13 TeV at the CERN LHC, corresponding to an integrated luminosity of 137 fb(-1) collected by the CMS experiment, is presented. Signatures with at least 2 jets and large missing transverse momentum are categorized into events with 0, 1, or 2 leptons. New results for regions of parameter space where the kinematical properties of top squark pair production and top quark pair production are very similar are presented. Depending on themodel, the combined result excludes a top squarkmass up to 1325 GeV for amassless neutralino, and a neutralinomass up to 700 GeV for a top squarkmass of 1150 GeV. Top squarks with masses from 145 to 295 GeV, for neutralino masses from 0 to 100 GeV, with a mass difference between the top squark and the neutralino in a window of 30 GeV around the mass of the top quark, are excluded for the first time with CMS data. The results of theses searches are also interpreted in an alternative signal model of dark matter production via a spin-0 mediator in association with a top quark pair. Upper limits are set on the cross section for mediator particle masses of up to 420 GeV

    MUSiC : a model-unspecific search for new physics in proton-proton collisions at root s=13TeV