My most recent project, aDetector, is coming along nicely. After a few more days of development it’s reached the stage where a detector can be assembled from a series of tracking systems and calorimeters, and simulate the decay of $$J/\psi$$ mesons to pairs of leptons. The leptons propagate through the detector, following helical paths in the presence of a uniform magnetic field, and lose energy as they interact with the various components in ways characteristic to each particle and component.