Search for the exclusive W boson hadronic decays $W^{\pm } \to \pi ^{\pm }\gamma, W^{\pm }\to K^{\pm }\gamma$ and $W^{\pm }\to \rho^{\pm }\gamma$ with the ATLAS Detector

A search for the exclusive hadronic decays $W^{\pm } \to \pi ^{\pm }\gamma, W^{\pm }\to K^{\pm }\gamma$ and $W^{\pm }\to p^{\pm }\gamma$ is performed using up to 140 fb$^{-1}$ of proton-proton collisions recorded with the ATLAS detector at a center-of-mass energy of $\sqrt{s}$ = 13 TeV. If observed, these rare processes would provide a unique test bench for the quantum chromodynamics factorization formalism used to calculate cross sections at colliders. Additionally, at future colliders, these decays could offer a new way to measure the W boson mass through fully reconstructed decay products. The search results in the most stringent upper limits to date on the branching fractions $\mathcal{B}(W^{\pm} \to \pi^{\pm}\gamma)$ < 1.9 $\times$ 10$^{-6}$, $\mathcal{B}(W^{\pm} \to K^{\pm}\gamma)$ < 1.7 $\times$ 10$^{-6}$, $\mathcal{B}(W^{\pm} \to \rho^{\pm}\gamma)$ < 5.2 $\times$ 10$^{-6}$ at 95% confidence level.