Tests of the CPT Invariance at the Antiproton Decelerator of CERN

The Standard Model, the theory of particle physics is based on symmetries: both the structure of the composite particles and their interactions are derived using gauge invariance principles. Some of these are violated by the weak interaction like parity and CP symmetry, and even masses are created via spontaneous symmetry breaking. CPT invariance, the most essential symmetry of the Standard Model, states the equivalency of matter and antimatter. However, because of the lack of antimatter in our Universe it is continuously tested at CERN. We overview these experiments: measuring the properties of antiprotons as compared to those of the proton at the Antiproton Decelerator and also searching for antimatter in cosmic rays.

The ATHENA experiment for the study of antihydrogen

In 2002, the ATHENA experiment was the first to produce large amounts of antihydrogen atoms at the CERN Antiproton Decelerator (AD). In this review article, we collect and discuss all the relevant results of the experiment: antiproton and positron cooling and their recombination dynamics in the nested Penning trap, the methods used to unambiguously identify the antiatoms as well as the protonium background, the dependence of the antihydrogen formation on mixing time and temperature. An attempt to interpret the results in terms of the two-body and three-body formation reactions, taking into account the complicated nested-trap dynamics, is also made. The relevance of the ATHENA results on future experiments is discussed, together with a short overview of the current antimatter physics at the AD.

Past, present and future low energy antiproton facilities at CERN

Low energy antiprotons are available for physics experiments at CERN since the 1980s and have been used by a large variety of experiments. The Low Energy Antiproton Ring LEAR has been constructed as a complementary use of antiprotons available at that time for high energy physics and delivered beam to experiments mainly using slow extraction. After completion of LEAR exploitation, the Antiproton Decelerator (AD) was constructed (adaptation of the existing Antiproton Collector, AC) to allow for a simpler low energy antiproton scheme (only one accelerator operated with Antiprotons) with fast extraction well suited for trap experiments. The Extra Low ENergy Antiproton ring ELENA is a small synchrotron presently constructed to further decelerate antiprotons from the AD in a controlled manner, and to reduce emittances with the help of an electron cooler to improve the capture efficiencies of existing experiments and allow for additional ones.