Opticks : Optical Photon Simulation for Particle Physics using GPU Accelerated Ray Tracing

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A detailed understanding of the generation and propagation of optical photons is vital to the design, operation and analysis of photomultiplier based neutrino detectors such as the Daya Bay and JUNO experiments. Detailed detector simulations handling many millions of optical photons per interaction are used to develop the understanding required to make precision measurements. Traditional serial approaches using the Geant4 simulation toolkit suffer from an optical photon simulation problem where photon handling provides a processing bottleneck and constitutes a CPU memory resource limitation. I will present Opticks, https://bitbucket.org/simoncblyth/opticks, an open source project that is my solution to the optical photon simulation problem. Opticks works together with Geant4, replacing the the Geant4 optical photon simulation with an equivalent massively parallel optical simulation implemented on the GPU and accelerated with the NVIDIA OptiX ray tracing engine. Optical photon simulation performance with Opticks is extrapolated to exceed 1000x Geant4 with workstation GPU machines. Optical photon processing time becomes effectively zero and CPU memory constraints from the optical photons are eliminated. Also moving the simulation to the GPU has enabled unprecedented in the field visualizations to be developed. Although developed in the context of Geant4 based neutrino detector simulations the techniques used by Opticks are potentially applicable to any simulation that is limited by optical photon processing.