Production of antihydrogen at reduced magnetic field for anti-atom trapping

We have demonstrated production of antihydrogen in a 1 T solenoidal magnetic field. This field strength is significantly smaller than that used in the first generation experiments ATHENA (3 T) and ATRAP (5 T). The motivation for using a smaller magnetic field is to facilitate trapping of antihydrogen atoms in a neutral atom trap surrounding the production region. We report the results of measurements with the Antihydrogen Laser PHysics Apparatus (ALPHA) device, which can capture and cool antiprotons at 3 T, and then mix the antiprotons with positrons at 1 T. We infer antihydrogen production from the time structure of antiproton annihilations during mixing, using mixing with heated positrons as the null experiment, as demonstrated in ATHENA. Implications for antihydrogen trapping are discussed. (Some figures in this article are in colour only in the electronic version) Cold antihydrogen atoms were first synthesized and detected in 2002 [1] by the ATHENA collaboration at the CERN Antiproton Decelerator (AD) [2]. The neutral antihydrogen 12 Permanent address: Department of Physics, University of Wales Swansea, Swansea SA2 8PP, UK. 13 Permanent address: Rafael, POB 2250, Haifa 31021, Israel. 14 Permanent address: Physics Department, Technion, Haifa 32000, Israel. atoms were not confined; in fact, ATHENA detected the annihilation of the antiproton and positron in spatial and temporal coincidence to demonstrate antihydrogen production. The ATRAP collaboration reported a similar result, using an indirect detection technique based on field ionization [3], shortly thereafter. In both of the initial experiments, antihydrogen was produced by merging plasmas of antiprotons and positrons in liquid helium cooled Penning 0953-4075/08/011001+05$30.00 1 © 2008 IOP Publishing Ltd Printed in the UK J. Phys. B: At. Mol. Opt. Phys. 41 (2008) 011001 Fast Track Communication scintillators (1 of 4 shown) pbar catching mixing positrons positron transfer main solenoid (length indication) inner solenoid faraday cup/ final degrader left mirror octupole right mirror helium volume