Atomic antihydrogen has recently been observed at Fermilab [1]. It appears feasible to measure the principal structure, fine structure and Lamb shift of antihydrogen atoms in flight [2]. It is possible to test the proposed techniques and measure cross sections for the relevant atomic processes at relativistic velocities by first using a proton beam. We propose to perform such a test at the FNAL Booster using 8 GeV protons, either in the old transfer line from the Booster to the Main Ring (the proposed "silicon damage" test facility) or in the permanent magnet transfer line to the Main Injector. 1. Introduction CPT invariance is a fundamental assumption of quantum field theory and is widely believed to be an absolute symmetry of nature. The neutral K system provides the most accurate test of CPT invariance in weak interactions; a model dependent estimate of the K 0 K 0 mass difference is less than one part in 10 18 . The equality of proton and antiproton masses is known to one..
