Speaker
Description
We extract the elastic electromagnetic transition of a two-pion $I=2$ state across the two-pion elastic energy region using lattice QCD. In particular, we determine the energy dependence of a two-particle transition from lattice QCD for the first time. The finite-volume spectrum and elastic matrix elements were calculated on a lattice with $m_\pi\approx 400$ MeV. Infinite-volume amplitudes were then extracted by removing leading power-law finite-volume effects according to the Lüscher formalism and its extensions. This work provides a proof of principle, as the same finite-volume techniques can be applied to systems featuring shallow bound states or resonances, allowing for the removal of finite-volume effects in their form factor extractions. Access to the form factors of these states is an important step toward understanding of QCD and its confining mechanism, while also providing valuable constraints for electroweak interactions with multi-nucleon systems.