The ALPHA Experiment: Testing CPT and Gravity with Trapped Antihydrogen

Over the past decade, the ALPHA (Antihydrogen Laser Physics Apparatus) Collaboration at CERN has been working towards precision tests of fundamental symmetries between matter and antimatter [1-4]. Recently, we have succeeded in observing, for the first time, the 1s-2s transition in trapped antihydrogen [5]. The initial measurement had a sensitivity of 2x10$^{-10}$, and we expect a significant improvement in the near future. In the meantime, we are constructing a new apparatus, ALPHA-g, in order to measure the gravitational force on antimatter by dropping antihydrogen atoms. In this talk, I will give an overview and prospects of the ALPHA experiment. REFERENCES: [1] Andresen, G. B. et al. Trapped antihydrogen, {¥it Nature} 468, 673–676 (2010). [2] Andresen, G. B. et al. Confinement of antihydrogen for 1,000 seconds, Nature Physics 7, 558–564 (2011). [3] Amole, C. et al. Resonant quantum transitions in trapped antihydrogen atoms, Nature 483, 439–443 (2012). [4] Ahmadi, M. et al. An improved limit on the charge of antihydrogen from stochastic acceleration, Nature 529, 373–376 (2016). [5] Ahmadi, M. et al., Observation of the 1S-2S transition in trapped antihydrogen, Nature 541, 506-510 (2017).