Abstract
A search for flavor-changing neutral current interactions of the top quark (t) and the Higgs boson (H) is presented. The search is based on a data sample corresponding to an integrated luminosity of 137 fb−1 recorded by the CMS experiment at the LHC in proton-proton collisions at sqrt{s} = 13 TeV. Events containing exactly one lepton (muon or electron) and at least three jets, among which at least two are identified as originating from the hadronization of a bottom quark, are analyzed. A set of deep neural networks is used for kinematic event reconstruction, while boosted decision trees distinguish the signal from the background events. No significant excess over the background predictions is observed, and upper limits on the signal production cross sections are extracted. These limits are interpreted in terms of top quark decay branching fractions ( mathcal{B} ) to the Higgs boson and an up (u) or a charm quark (c). Assuming one nonvanishing extra coupling at a time, the observed (expected) upper limits at 95% confidence level are mathcal{B} (t → Hu) < 0.079 (0.11)% and mathcal{B} (t → Hc) < 0.094 (0.086)%.
Highlights
The CMS detectorThe central feature of the CMS apparatus is a superconducting solenoid of 6 m internal diameter, providing a magnetic field of 3.8 T
Most recent analysis is performed by CMS using a data sample with an integrated luminosity of 137 fb−1 in the diphoton decay channel of the Higgs boson, yielding observed limits on the branching fractions of 0.019 and 0.078% for t → Hu and t → Hc, respectively [25]
A set of deep neural networks is used for kinematic event reconstruction, while boosted decision trees distinguish the signal from the background events
Summary
The central feature of the CMS apparatus is a superconducting solenoid of 6 m internal diameter, providing a magnetic field of 3.8 T. There are a silicon pixel and strip tracker, a lead tungstate crystal electromagnetic calorimeter (ECAL), and a brass and scintillator hadron calorimeter (HCAL), each composed of a barrel and two endcap sections. Forward calorimeters extend the pseudorapidity (η) coverage provided by the barrel and endcap detectors. Events of interest are selected using a twotiered trigger system. The first level is composed of custom hardware processors and selects events at a rate of around 100 kHz [27]. The second level, known as the high-level trigger, is implemented in software running on a processor farm and reduces the event rate to around 1 kHz before data storage [28]. A more detailed description of the CMS detector, together with a definition of the coordinate system used and the relevant kinematic variables, can be found in ref. [29]
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