Model-independent partial wave analysis using a massively-parallel fitting framework

The functionality of GooFit, a GPU-friendly framework for doing maximum-likelihood fits, has been extended to extract model-independent ${\mathscr{S}}$-wave amplitudes in three-body decays such as D⁺ → h⁺h⁺h⁻. A full amplitude analysis is done where the magnitudes and phases of the ${\mathscr{S}}$-wave amplitudes are anchored at a finite number of m²(h⁺h⁻) control points, and a cubic spline is used to interpolate between these points. The amplitudes for ${\mathscr{P}}$-wave and ${\mathscr{D}}$-wave intermediate states are modeled as spin-dependent Breit-Wigner resonances. GooFit uses the Thrust library, with a CUDA backend for NVIDIA GPUs and an OpenMP backend for threads with conventional CPUs. Performance on a variety of platforms is compared. Executing on systems with GPUs is typically a few hundred times faster than executing the same algorithm on a single CPU.