The first observation of antihydrogen atoms was made at CERN in 1995, in experiment PS210 at LEAR. Antihydrogen atoms produced in flight moved at nearly the speed of light. They made unique electrical signals in detectors that destroyed them almost immediately after they formed. Eleven signals were observed, of which two were attributed to other processes. In 1997 similar observations were announced at Fermilab from experiment E862. The first measurement demonstrated the existence of antihydrogen, the second (with improved setup and intensity monitoring) measured the production rate. Both experiments, one at each of the only two facilities with suitable antiprotons, were stimulated by calculations which suggested the possibility of making very fast antihydrogen within existing circular accelerators. The measured production rate agreed with an improved calculation.
The existence of antihydrogen was verified by the observations of hot, fast antihydrogen atoms. Now the focus returns to extremely accurate comparisons of the properties of hydrogen and antihydrogen that are the goals of ATRAP (and TRAP earlier). The hot antihydrogen atoms are moving much too fast to allow measurements to be carried out at an interesting level of accuracy. Properties of the fast atoms cannot be measured accurately in the much too short time it takes to pass through an apparatus. It also seems unlikely that large numbers of fast atoms will ever be made.
The goal of ATRAP is to produce cold antihydrogen which moves slowly enough to make measurements of an extremely high precision. Alongside the very accurate and successful comparison of the charge-to-mass ratio of antiprotons and protons, the TRAP program to produce the ingredients of cold antihydrogen was well underway, and had made good progress, long before the possibility of observing hot antihydrogen atoms was proposed or realized. Insofar as an accurate comparison of the properties of antihydrogen atoms and hydrogen atoms can only be carried out with cold atoms, several members of PS210 (including PS210 spokesperson W. Oelert) now participate in ATRAP.
Calculation suggests the possibility to observe
hot, fast antihydrogen at existing accelerators.
"Electromagnetic pair production with capture"
A.Aste et al.
Phys. Rev. A 50 (1994) 3980.
First experimental observations (at CERN) attributed
to hot, fast antihydrogen.
"Production of Antihydrogen"
G.Baur et al. (includes D. Grzonka, W. Oelert, G. Schepers, and T. Sefzick, now part of ATRAP)
Phys.Lett. B 368 (1996) 251-258.
Improved calculation predicts production rates
that are much lower.
(Production cross sections based upon this calculation are in the Blanford PRL below)
"Anti-hydrogen Production and Accuracy of the Equivalent Photon Approximation"
C.A. Bertulani and G. Baur
Phys. Rev. D58, 34005 (1998).
Second observations (at Fermilab, with improved
setup and luminosity monitors) attributed to hot, fast antihydrogen atoms.
"Observation of Antihydrogen"
G. Blanford, et al.
Phys. Rev. Lett. 80, 3037 (1998).