{"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 energy conservation and momentum conservation in relativistic contexts.", "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, given their energies and directions.", "goal": "Calculate the angle between the two emitted photons based on their momentum vectors and the conservation laws."}, "summary": "This problem involves the collision of an electron and a positron, resulting in the production of two photons. The key to solving it lies in applying the principles of conservation of energy and momentum in a relativistic framework. Given that both photons have the same energy and are emitted in different directions, we can use vector analysis to find the angle between their trajectories. The answer will be one of the provided candidates based on the calculations."}