Antihydrogen

Antihydrogen (H) is the antimatter counterpart of hydrogen. Whereas the common hydrogen atom is composed of an electron and proton, the antihydrogen atom is made up of a positron and antiproton. Scientists hope studying antihydrogen may shed light on the question of why there is more matter than antimatter in the observable universe, known as the baryon asymmetry problem. Antihydrogen is produced artificially in particle accelerators. In 1999, NASA gave a cost estimate of $62.5 trillion per gram of antihydrogen (equivalent to $94 trillion today), making it the most expensive material to produce. This is due to the extremely low yield per experiment, and high opportunity cost of using a particle accelerator. Antihydrogen (H) is the antimatter counterpart of hydrogen. Whereas the common hydrogen atom is composed of an electron and proton, the antihydrogen atom is made up of a positron and antiproton. Scientists hope studying antihydrogen may shed light on the question of why there is more matter than antimatter in the observable universe, known as the baryon asymmetry problem. Antihydrogen is produced artificially in particle accelerators. In 1999, NASA gave a cost estimate of $62.5 trillion per gram of antihydrogen (equivalent to $94 trillion today), making it the most expensive material to produce. This is due to the extremely low yield per experiment, and high opportunity cost of using a particle accelerator. Accelerators first detected hot antihydrogen in the 1990s. ATHENA studied cold H in 2002. It was first trapped by the Antihydrogen Laser Physics Apparatus (ALPHA) team at CERN in 2010, who then measured the structure and other important properties. ALPHA, AEGIS, and GBAR plan to further cool and study H atoms. In 2016, the ALPHA experiment measured the atomic electron transition between the two lowest energy levels of antihydrogen, 1S–2S. The results, which are identical to that of hydrogen within the experimental resolution, support the idea of matter–antimatter symmetry and CPT symmetry. In the presence of a magnetic field the 1S–2S transition splits into two hyperfine transitions with slightly different frequencies. The team calculated the transition frequencies for normal hydrogen under the magnetic field in the confinement volume as: A single-photon transition between S states is prohibited by quantum selection rules, so to elevate ground state positrons to the 2S level, the confinement space was illuminated by a laser tuned to half the calculated transition frequencies, stimulating allowed two photon absorption.