CPT tests with antihydrogen and antiprotonic helium atoms

Recent progress of the CPT tests with antihydrogen and antiprotonic helium atoms by the ASACUSA collaboration at CERN's antiproton decelerator will be presented. The antiprotonic helium atom (antiproton+electron+helium nucleus) is a serendipitously discovered metastable three-body system, whose energy levels can now be studied by laser spectroscopy techniques to a relative precision of $\sim 10^{-9}$ [1]. By comparing these precise experimental results with the result of three-body QED calculation [2], the antiproton-to-electron mass ratio was determined to a relative precision of $1.2\times 10^{-9}$. While this can be used as a precise test of the CPT symmetry [3], CODATA instead assumed the CPT, and combined our results with the proton-to-electron mass ratio measured by the Penning trap method in their adjustment of the fundamental physical constants [4]. In addition to the laser spectroscopy of antiprotonic helium, ASACUSA collaboration also aims at measuring the ground-state hyperfine splitting of antihydrogen using the (anti)-atomic beam method. Extraction of antihydrogen atoms from a ``cusp'' trap has so far been demonstrated [5]. Both of these experiments will benefit from the completing of a new antiproton decelerator-cooler ring called ELENA, which is under construction at CERN. \\[4pt] [1] Hori M. et al., Nature 475, 484 (2011).\\[0pt] [2] Korobov V.I., Phys. Rev. A 89, 014501 (2014).\\[0pt] [3] Hayano R.S. et al, Rep. Prog. Phys. 70, 1995 (2007).\\[0pt] [4] Mohr P.J., Taylor B.N., Newell D.B., Rev. Mod. Phys. 84, 1527 (2012).\\[0pt] [5] Kuroda N. et al, Nature Communications 5, 3089 (2014).\\[0pt] [6] ELENA design report, CERN-2014-002.