Wgamma

Wgamma refers to the production of a W boson in association with a photon in high-energy particle collisions. It is an electroweak process predicted by the Standard Model and serves as a probe of the WWγ trilinear gauge coupling and electroweak radiative corrections. Measurements of Wγ production tests the consistency of the gauge structure of the theory and can be sensitive to physics beyond the Standard Model through anomalous couplings.

In proton-proton or proton-antiproton collisions, Wγ production occurs primarily through quark-antiquark annihilation involving the WWγ vertex. Additional contributions arise from initial-state radiation of a photon by incoming quarks and from final-state radiation by the charged lepton or hadronic decay products of the W. Higher-order quantum chromodynamics corrections and parton-shapings play a significant role in shaping predicted cross sections and kinematic distributions.

Experimentally, the typical signature is a W boson decaying leptonically (to a charged lepton and a neutrino) accompanied by a prompt photon. This yields events with a high-transverse-momentum lepton, missing transverse energy from the neutrino, and a photon. Key backgrounds include W+jets with a jet misidentified as a photon, Zγ production, and diboson processes. Observables include the cross section, photon transverse energy distributions, and angular separations between the photon and the lepton or W decay products.

Theoretical work includes calculations at next-to-leading order or higher, modeling of QCD and electroweak corrections, and frameworks for setting limits on anomalous WWγ couplings. Experimental results from colliders such as the Tevatron and the Large Hadron Collider have generally found agreement with Standard Model predictions within uncertainties, while continuing to constrain possible new physics effects.