  The ASACUSA (Atomic Spectroscopy And Collisions Using Slow Antiprotons)
collaboration plans to measure the ground-state hyperfine splitting of
antihydrogen in a beam at the CERN Antiproton Decelerator with initial relative
precision of 10-6 or better, to test the fundamental CPT (combination of charge
conjugation, parity transformation and time reversal) symmetry between matter
and antimatter. This challenging goal requires a polarised antihydrogen beam
with a sufficient number of antihydrogen atoms in the ground state. The first
measurement of the quantum state distribution of antihydrogen atoms in a low
magnetic field environment of a few mT is described. Furthermore, the
data-driven machine learning analysis to identify antihydrogen events is
discussed.
