In a giant particle accelerator, particles smash into each other, and sometimes after the collision only two photons, particles of light, remain. Physicists can predict how often this happens, but their calculations have long disagreed with what detectors see. Each refinement of the theory changed the answer, and there was no consensus.

The authors of the new work took another step in precision: they added the next level of corrections to the calculation. It's like tuning a radio: at first you hear only static, but with each turn of the dial, the signal becomes clearer. Now the calculation finally matches the experiment, and physicists can trust their predictions.

Such a precise calculation is not needed for its own sake. When searching for new particles at the collider, they may decay into two photons. To spot a signal from new physics, you need to know exactly how many such pairs are produced by ordinary processes. Now this background is calculated reliably, and the search becomes cleaner.