Comparing the antiproton and proton and progress toward cold antihydrogen

The most stringent test of CPT invariance with a baryon system is a 1 part in 10⁹ comparison of the charge-to-mass ratios of the antiproton and proton. An improved Q/M comparison for antiproton and protons at the 10^-10 level of accuracy is underway, utilizing an antiproton and an II^- ion confined at the same time in a Penning trap. Precise spectroscopic comparisons of cold antihydrogen and hydrogen atoms should produce much more accurate CPT tests. The recent experimental progress toward cold antihydrogen includes the accumulation of more than a million 4.2 K positrons in ultrahigh vacuum, and a demonstrated low temperature interaction of cold electrons and protons in a nested Penning trap. The first attempt at producing cold antihydrogen is scheduled for late 1996. Collaborations and facilities for antihydrogen studies after 1996 will be mentioned.