One goal of future studies with antihydrogen will be to compare its spectroscopy with hydrogen’s. This will require the antihydrogen atoms to be trapped long enough for precise measurements to be made, which in turn will need very low antihydrogen temperatures, well below 0.5 K. The ATRAP collaboration at the AD has been experimenting with a new way of producing antihydrogen that might result in suitably low temperatures.
Until now, antihydrogen production has been achieved by bringing cooled antiprotons and positrons together in a nested Penning trap structure. The new method consists of exciting caesium atoms from an oven with two lasers, and then introducing the caesium into a positron trap. Excited positronium, a bound state of an electron and a positron, is then formed when a positron collides with a caesium atom and captures an electron. These positronium atoms carry virtually all the 10 meV or so binding energy of the caesium atoms. Finally, a fraction of the excited positronium atoms collide with trapped antiprotons to produce excited antihydrogen atoms with a probability that is expected to be much higher than for ground-state positronium.
The velocity distribution of the resulting excited antihydrogen is expected to be the same as that of the trapped antiprotons from which the antihydrogen forms, which can be made arbitrarily low in principle. Verifying this by directly measuring the antihydrogen velocity has not yet been possible, but if the low antihydrogen energy is confirmed, and if the highly excited states can be de-excited, this technique could become the method of choice for producing cold antihydrogen for precise spectroscopic analysis.
C H Storry et al. 2004 Phys. Rev. Lett. 93 263401.