DENVER — The size of a proton, long thought to be well-understood, may remain a mystery for a while longer, according to physicists. Speaking today (April 13) at the April meeting of the American Physical Society, researchers said they need more data to understand why new measurements of proton size don't match old ones. "The discrepancy is rather severe," said Randolf Pohl, a scientist at the Max Planck Institute of Quantum Optics. The question, Pohl and his colleagues said, is whether the explanation is a boring one — someone messed up the measurements — or something that will generate new...