Prospects of In-Flight Hyperfine Spectroscopy of (Anti)Hydrogen for   Tests of CPT Symmetry
  The ground-state hyperfine splitting of antihydrogen promises one of the most sensitive tests of CPT symmetry. The ASACUSA collaboration is pursuing a measurement of this splitting in a Rabi-type experiment using a polarized beam from a CUSP magnet at the Antiproton Decelerator of CERN. With the initial intention of characterizing the Rabi apparatus, a polarized source of cold hydrogen was built and the $\sigma_1$ transition of hydrogen was measured to a few ppb precision. A measurement of the $\pi_1$ transition is being prepared. The availability of this beam opens the possibility to perform first measurements of some coefficients within the nonminimal Standard-Model Extension. 
Eberhard Widmann
hep-ex hep-ph physics.atom-ph