Resonant π^{+}γ→π^{+}π^{0} Amplitude from Quantum Chromodynamics

• Published in: Physical review letters 2015-12, Vol.115 (24), p.242001-242001
• Main Authors: Briceño, Raúl A, Dudek, Jozef J, Edwards, Robert G, Shultz, Christian J, Thomas, Christopher E, Wilson, David J
• Format: Article
• Language: English
• ISSN: 1079-7114
• DOI: 10.1103/PhysRevLett.115.242001

We present the first ab initio calculation of a radiative transition of a hadronic resonance within quantum chromodynamics (QCD). We compute the amplitude for ππ→πγ^{⋆}, as a function of the energy of the ππ pair and the virtuality of the photon, in the kinematic regime where ππ couples strongly to the unstable ρ resonance. This exploratory calculation is performed using a lattice discretization of QCD with quark masses corresponding to m_{π}≈400  MeV. We obtain a description of the energy dependence of the transition amplitude, constrained at 48 kinematic points, that we can analytically continue to the ρ pole and identify from its residue the ρ→πγ^{⋆} form factor.