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

This thesis presents a measurement of the production of a Standard Model Higgs boson in association with a top quark-antiquark pair ($\text{t}\bar{\text{t}}\text{H}$), where the Higgs boson in candidate $\text{t}\bar{\text{t}}\text{H}$ events is required to decay into a bottom quark-antiquark pair ($\text{t}\bar{\text{t}}\text{H}(\text{b}\bar{\text{b}})$). 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$\,\text{fb}^{-1}$. In particular, the semileptonic decay mode of the $\text{t}\bar{\text{t}}$ 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 $\text{t}\bar{\text{t}}\text{H}(\text{b}\bar{\text{b}})$ process with respect to the Standard Model prediction $\mu = \sigma^\text{obs}/\sigma^\text{SM}$ are performed. Therefore, the sensitivity expected within the scope of the Standard Model prediction is discussed, which corresponds to an expected significance of $3.3\,$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 $\text{t}\bar{\text{t}}$ 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 $\text{t}\bar{\text{t}}\text{H}(\text{b}\bar{\text{b}})$ process within the CMS experiment. Finally, the sensitivity for $\text{t}\bar{\text{t}}\text{H}(\text{b}\bar{\text{b}})$ measurements with future data sets is discussed, which is expected to reach approximately $7\,\%$ 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

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

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

Results of the Model Unspecific Search in CMS (MUSiC), using proton-proton collision data recorded at the LHC at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9 fb(-1), are presented. The MUSiC analysis searches for anomalies that could be signatures of physics beyond the standard model. The analysis is based on the comparison of observed data with the standard model prediction, as determined from simulation, in several hundred final states and multiple kinematic distributions. Events containing at least one electron or muon are classified based on their final state topology, and an automated search algorithm surveys the observed data for deviations from the prediction. The sensitivity of the search is validated using multiple methods. No significant deviations from the predictions have been observed. For a wide range of final state topologies, agreement is found between the data and the standard model simulation. This analysis complements dedicated search analyses by significantly expanding the range of final states covered using a model independent approach with the largest data set to date to probe phase space regions beyond the reach of previous general searches.Peer reviewe

Measurement of prompt open-charm production cross sections in proton-proton collisions at root s=13 TeV

The production cross sections for prompt open-charm mesons in proton-proton collisions at a center-of-mass energy of 13TeV are reported. The measurement is performed using a data sample collected by the CMS experiment corresponding to an integrated luminosity of 29 nb(-1). The differential production cross sections of the D*(+/-), D-+/-, and D-0 ((D) over bar (0)) mesons are presented in ranges of transverse momentum and pseudorapidity 4 < p(T) < 100 GeV and vertical bar eta vertical bar < 2.1, respectively. The results are compared to several theoretical calculations and to previous measurements.Peer reviewe

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

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

Measurement of B-c(2S)(+) and B-c*(2S)(+) cross section ratios in proton-proton collisions at root s=13 TeV

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Search for new particles in events with energetic jets and large missing transverse momentum in proton-proton collisions at root s=13 TeV

A search is presented for new particles produced at the LHC in proton-proton collisions at root s = 13 TeV, using events with energetic jets and large missing transverse momentum. The analysis is based on a data sample corresponding to an integrated luminosity of 101 fb(-1), collected in 2017-2018 with the CMS detector. Machine learning techniques are used to define separate categories for events with narrow jets from initial-state radiation and events with large-radius jets consistent with a hadronic decay of a W or Z boson. A statistical combination is made with an earlier search based on a data sample of 36 fb(-1), collected in 2016. No significant excess of events is observed with respect to the standard model background expectation determined from control samples in data. The results are interpreted in terms of limits on the branching fraction of an invisible decay of the Higgs boson, as well as constraints on simplified models of dark matter, on first-generation scalar leptoquarks decaying to quarks and neutrinos, and on models with large extra dimensions. Several of the new limits, specifically for spin-1 dark matter mediators, pseudoscalar mediators, colored mediators, and leptoquarks, are the most restrictive to date.Peer reviewe

Measurements of the Electroweak Diboson Production Cross Sections in Proton-Proton Collisions at root s=5.02 TeV Using Leptonic Decays

The first measurements of diboson production cross sections in proton-proton interactions at a center-of-mass energy of 5.02 TeV are reported. They are based on data collected with the CMS detector at the LHC, corresponding to an integrated luminosity of 302 pb(-1). Events with two, three, or four charged light leptons (electrons or muons) in the final state are analyzed. The WW, WZ, and ZZ total cross sections are measured as sigma(WW) = 37:0(-5.2)(+5.5) (stat)(-2.6)(+2.7) (syst) pb, sigma(WZ) = 6.4(-2.1)(+2.5) (stat)(-0.3)(+0.5)(syst) pb, and sigma(ZZ) = 5.3(-2.1)(+2.5)(stat)(-0.4)(+0.5) (syst) pb. All measurements are in good agreement with theoretical calculations at combined next-to-next-to-leading order quantum chromodynamics and next-to-leading order electroweak accuracy

Measurement of the top quark Yukawa coupling from t(t)over-bar kinematic distributions in the dilepton final state in proton-proton collisions at root s=13 TeV

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Search for lepton-flavor violating decays of the Higgs boson in the mu tau and e tau final states in proton-proton collisions at root s=13 TeV

A search is presented for lepton-flavor violating decays of the Higgs boson to mu t and et. The dataset corresponds to an integrated luminosity of 137 fb(-1) collected at the LHC in proton-proton collisions at a center-of-mass energy of 13 TeV. No significant excess has been found, and the results are interpreted in terms of upper limits on lepton-flavor violating branching fractions of the Higgs boson. The observed (expected) upper limits on the branching fractions are, respectively, B(H -> mu t) e tau) < 0.22(0.16)% at 95% confidence level.Peer reviewe