Search for the Exclusive W Boson Hadronic Decays W^±→ π^±γ, W^±→ K^±γ and W^±→ ρ^±γ with the ATLAS Detector

A search for the exclusive hadronic decays 𝑊^± → 𝜋^±⁢𝛾, 𝑊^± → 𝐾^±⁢𝛾, and 𝑊^± →𝜌^±⁢𝛾 is performed using up to 140  fb⁻¹ of proton-proton collisions recorded with the ATLAS detector at a center-of-mass energy of √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 ℬ⁡(𝑊^± → 𝜋^±⁢𝛾)<1.9 × 10⁻⁶, ℬ⁡(𝑊± → 𝐾^±⁢𝛾)<1.7 × 10⁻⁶, ℬ⁡(𝑊^± → 𝜌^±⁢𝛾)<5.2 × 10⁻⁶ at 95% confidence level.