{"knowledge_schema": {"broad_category": "Physics \u2192 Relativity \u2192 Particle Physics", "refinement": "This problem involves the collision of particles (electron and positron) and the subsequent annihilation event that produces photons, requiring an understanding of relativistic energy and momentum conservation.", "specific_scope": "The focus is on determining the angle between the directions of two photons produced from the annihilation of an electron and a positron, taking into account their respective Lorentz factors and motion directions.", "goal": "Calculate the angle between the two emitted photons based on the conservation of momentum and energy principles in a relativistic context."}, "summary": "This problem is rooted in the principles of relativistic physics, specifically dealing with particle collisions and the resulting photon emissions. An electron and a positron collide, annihilating each other and producing two photons with equal energy. The task is to find the angle between the directions of these photons, which can be determined using conservation laws. The answer to the angle between the photons is 138 degrees."}