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 140fb⁻¹ of proton-proton collisions recorded with the ATLAS detector at a center-of-mass energy of √s = 13TeV. These rare processes provide a test bench for the quantum chromodynamics factorization formalism used to calculate cross sections at colliders, as well as a probe of W boson coupling to quarks and a new way to measure the W boson mass through fully reconstructed decay products. The search results in the most stringent upper limit 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.