Real-time dual-telescope normalization for absorption muography: an improved density estimation approach

Absorption muography infers path-averaged density from the attenuation of atmospheric muons; however, transient flux variations due to weather, solar activity, and geomagnetism bias sequential measurements that rely on non-simultaneous backgrounds. We demonstrate real-time dual-telescope normalization using two identical plastic scintillator–PMT telescopes operated in parallel: one views open sky (reference), the other the target (main). Their count-rate ratio cancels common-mode flux changes and tracks detector drift. A 140-h no-target run yields a stable calibration, and stacked acrylic slabs give an empirical transmission–thickness curve. Minimum-ionizing events are selected with a robust valley-bounded pulse-height window. Transmissions are fitted with a weighted exponential and cross-checked by a Bayesian variant. Applied to blind targets, the dual-mode recovers the densities of 20-cm aluminum and 10-cm stainless-steel blocks within uncertainties, whereas a single-telescope workflow shows significant biases. A compact vertical stack improves common-mode rejection. The method reduces systematics and is directly applicable to field deployments.