Speaker
Description
Comparisons of hydrogen to antihydrogen provide an excellent test of CPT symmetry, particularly in identifying any symmetry breaking between matter and antimatter. The energy levels of atomic hydrogen are some of the most precisely characterised quantities in nature, the challenge therefore lies in measuring the properties of antihydrogen to the same level of precision to make a meaningful comparison.
The ASACUSA experiment, based at the Antiproton Decelerator facility at CERN, aims to measure the ground state hyperfine structure of antihydrogen for this purpose [1]. The initial target is 10 ppm precision using a Rabi type microwave excitation, the apparatus of which has been built for a polarized antihydrogen beam of velocity <1500 m/s [2]. The use of a beam removes the antihydrogen from the high magnetic fields (~2 T) required in the antihydrogen production process [3], which are a major source of systematic error.
The ASACUSA antihydrogen beam is produced by slowly merging cold antiproton and positron plasmas over a 120 s period, during which antihydrogen is formed by three-body recombination. The beam has an intensity of up to 320 antihydrogen per 15 minute production cycle, the highest antihydrogen beam intensity achieved. I will present the key properties of the antihydrogen beam, including velocity and principle quantum number distribution, and show the current status of the ASACUSA experiment.
[1] E. Widmann, et al., NIM B 214, 31-34 (2009).
[2] C. Malbrunot et al., NIM A 935, 110-120 (2019).
[3] The ALPHA Collaboration, Nat. Comm. 8 (2017).