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| Home > Publications database > Event Selection and Angular Reconstruction for W Boson Events at Future $e^+e^-$ Colliders |
| Master Thesis | PUBDB-2024-07665 |
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2024
Abstract: The international particle physics community has identified an e+e− Higgs factory as the highest-priority next collider. Such a facility would enable the production of a substantial number ofW bosons. For instance, the ILC would produce 1.2 × 108 W bosons at 250 and 500 GeV, while the FCC program offers similar production rates at 160 and 240 GeV. The production processescomprise W -pair production and single-W production. Both are sensitive to beam polarisation and suited to scrutinize self-couplings of the gauge bosons in the electroweak sector. The measurements of these couplings are a validity test of the Standard Model (SM) with unprecedented precision due to the nature of electron-positron collisions. In addition, the hadronic decays of Wbosons probe elements of the CKM matrix. The goal is to reconstruct the W boson properties through its decay modes. These events correspond to a four fermions final state, being classifiedas semi-leptonic qqℓν, hadronic qqqq, or leptonic ℓνℓν. The work of this thesis consists of building a algorithm capable of a generic categorisation for W boson events and to defineoverlap-free pre-selections for all channels. This event selection will be of use for several analyses on the W decays. This work is based on mini-DST, the lighter successor of the Data Storage Technique (DST) data formats using a full Geant4 based simulation of the International Large Detector (ILD). The categorisation performance is evaluated by a confusion matrix and in each bin we give an efficiency (fraction of events desired). The diagonal of this matrix represents correctly categorised events, based on their Monte-Carlo (MC) truth, for which, after generic channel cuts on event observables, primary lepton correction and reducing beam-induced background, we achieve a final efficiency of 97.8% for the hadronic, 77.6% for single-W , 76.2% for semi-leptonic electron, 92.5% for semi-leptonic muon, 62.1% for semi-leptonic tau , and 98.2% for the leptonic channel. Finally, we do a direct comparison to the angular distributions measured at the Large Electron-Positron Collider (LEP) for the qqµν channel. The work of this thesis is in natural units (c = e = ℏ = 1).
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