Precision mass measurements of antiprotons in a penning trap

Utilizing electron cooling, the TRAP collaboration has lowered the energy at which antiprotons can be stored and studied by more than 10 orders of magnitude, starting with 6 MeV particles from LEAR. We have held cryogenic antiprotons a few degrees above absolute zero for two months and the storage lifetime so established, more than 3.4 months is the longest directly measured limit for antiprotons. Measuring their cyclotron frequencies in a precision cylindrical Penning trap, we have shown that the inertial masses of the antiprotons and protons are the same to a fractional accuracy of 4 parts in 10^sa 1000-fold improvement over the previous comparisons. This is the most stringent test of CPT invariance with baryons. We have recently demonstrated a linewidth resolution of more than 10 times narrower than our current measurement accuracy, making possible a new series of systematic tests to improve the accuracy by one or even two orders of magnitude.