Search for rare exclusive hadronic decays of the W boson with the ATLAS experiment

Cardoso Silva, Julia Manuela ORCID: 0000-0002-5987-2984 (2024). Search for rare exclusive hadronic decays of the W boson with the ATLAS experiment. University of Birmingham. Ph.D.

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Abstract

The search for rare exclusive hadronic decays of the Wboson in the \(W\rightarrow\pi\gamma\), \(W\rightarrow K \gamma\) and \(W\rightarrow\rho \gamma\) final states is presented. This search was performed using up to 140 fb\(^{-1}\) of proton collision data collected by the ATLAS experiment at a center-of-mass energy of \(\sqrt{s}\) =13 TeV. These decays can serve as clean probes of the QCD factorisation formalism and, in the future, could offer a new way to perform the W boson mass measurement, through fully reconstructed final states. Upper limits at 95 % CL are set on the branching fractions of the decays: B(\(W\rightarrow\pi\gamma\)) < 1.9x10\(^{-6}\), B(\(W\rightarrow K \gamma\)) < 1.7x10\(^{-6}\) and B(\(W\rightarrow\rho\gamma\)) < 5.4x10\(^{-6}\). These results correspond to the first experimental constraints on B(\(W\rightarrow K \gamma\)) and B(\(W\rightarrow\rho\gamma\)), and the most stringent upper limit to date on B(\(W\rightarrow\pi\gamma\)). This analysis was enabled by the use of dedicated triggers and of a novel, data-driven non-parametric background modelling technique. Detailed characterisation and validation studies of this novel background modelling method are also presented.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):