Answer:
All accelerator physics is theoretical physics.
It was once said that accelerator physics was like analyzing a modern Swiss watch by shooting it with a high power bullet1 and determining how it is made by analyzing the fragment patterns that result.
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1Source uncertain. If someone knows the reference, please refine this answer and provide it.
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No help on source but, I believe the quote goes: "It's like smashing a clock off the wall in a hope to figure out how it works by looking at the flying pieces."