Bruno Rossi used penetrating cosmic-ray particles to test relativistic particle lifetimes. His experiment with David B. Hall compared particles selected by momentum and examined how many survived propagation through the atmosphere.
The decay probability depends on the proper time elapsed along the particle's path. Faster particles can travel farther in the laboratory because their rest-frame clock accumulates less proper time over a given laboratory interval. The measured momentum dependence connected an observed particle population to time dilation.[ref]
Variation of the Rate of Decay of Mesotrons with Momentum by Bruno Rossi and David B. Hall. 1941 experiment: momentum selection, atmospheric survival and decay interpretation
Rossi also coauthored the early rocket detection of extrasolar X-rays, extending astronomical measurement beyond wavelengths accessible through the atmosphere.[ref]
Portrait of Bruno Rossi
. Massachusetts Institute of Technology. CC BY-SA 3.0, via Wikimedia Commons. Source.
