Past exam of the particle physics course of the University of Oxford / 2022 / 6 / d / ii

Matched near and far particle detectors are a good design. A near particle detector, close enough that the fast oscillation phase is small, measures the unoscillated reactor spectrum and normalization. A far particle detector near the first fast maximum measures the disappearance. Their appropriately geometry-corrected ratio cancels much of the uncertain reactor flux and common cross section and detection efficiency. Relative calibration, different backgrounds, multiple reactor distances and any residual near-site oscillation still need treatment. The near site should retain enough shielding to suppress cosmic backgrounds.^[ref]