A study of the radiative transition ππ → πγ∗ with lattice QCD

Abstract

Lattice QCD calculations of radiative transitions between hadrons have in the past been limited to processes of hadrons stable under the strong interaction. Recently developed methods for 1 → 2 transition matrix elements in a finite volume now enable the determination of radiative decay rates of strongly unstable particles. Our lattice QCD study focuses on the process ππ → πγ∗, where the ρ meson is present as an enhancement in the cross-section. We use 2+1 flavors of clover fermions at a pion mass of approximately 320 MeV and a lattice size of approximately 3.6 fm. The required 2-point and 3-point correlation functions are constructed from a set of forward, sequential and stochastic light quark propagators. In addition to determining the ρ meson resonance parameters via the Lüscher method, the scattering phase shift is used in conjunction with the 1 → 2 transition matrix element formalism of Briceño, Hansen and Walker-Loud [1] to compute the ππ → πγ∗ amplitude at several values of the momentum transfer and pp invariant mass. © Copyright owned by the author(s).