Measurements of Properties of Antihydrogen

The ALPHA project at the CERN AD is testing fundamental symmetries between matter and antimatter using trapped antihydrogen atoms. The spectrum of the antihydrogen atom may be compared to ordinary hydrogen where it has been measured very precisely. CPT conservation, which underpins our current theoretical framework, requires equality of the masses and charges of matter and its antimatter partners, so antihydrogen spectroscopy presents a path to precision CPT tests. I will discuss the techniques used by ALPHA to trap more than 8000 antihydrogen atoms in 2016, and interrogate them for 600s. The 1S-2S transition in antihydrogen has been observed for the first time, and it agrees with its hydrogen counterpart within an uncertainty of 400 kHz or 0.2 ppb. The charge of the antihydrogen atom has been bounded below [Formula: see text]. A value of 1420.4 0.5MHz for the hyperfine splitting has been obtained from observation of the positron spin resonance spectrum.