Abstract
The riddle of the baryon asymmetry, i.e. the matter antimatter imbalance in the universe can be addressed by comparing matter particles with their antimatter counterparts. At the antiproton decelerator (AD) at CERN several antimatter experiments investigate whether CPT (charge-parity-time reversal) invariance and the WEP (weak equivalence principle) hold. The systems probed are antihydrogen (), antiprotonic helium and individual antiprotons (). This article is meant to give an overview of the experiments located at the AD, discuss some commonly used experimental techniques and point out what the different experimental approaches entail. The research done on low-energy antimatter systems can be seen as complementary to the high energy research carried out at CERN and elsewhere: It provides bounds on CPT invariance and directly addresses the question of whether the WEP holds for antimatter. It is noted that the AD - at the moment - is the only low-energy antiproton source on earth.
Highlights
Despite the striking success in deciphering the inner workings of matter in particle physics, there is so far no answer to a simple question stemming from cosmology - the matter-antimatter asymmetry
The riddle of the baryon asymmetry, i.e. the matter antimatter imbalance in the universe can be addressed by comparing matter particles with their antimatter counterparts
At the antiproton decelerator (AD) at CERN several antimatter experiments investigate whether charge-parity-time reversal (CPT) invariance and the weak equivalence principle (WEP) hold
Summary
Despite the striking success in deciphering the inner workings of matter in particle physics, there is so far no answer to a simple question stemming from cosmology - the matter-antimatter asymmetry. The prerequesites to testing either CPT symmetry or WEP in the domain of low-energy antimatter physics are to efficiently trap and cool antiprotons in a Penning-Malmberg trap or to form a beam of antiprotons cold enough so it can be more manipulated (e.g. focused to a smaller diameter) and used in an experimental protocol. To facilitate the formation of low-energy antihydrogen needed for spectroscopy the antiprotons can be carefully mixed with the positrons by slowly manipulating the nested trap potentials instead of releasing the antiproton cloud into the positron plasma like in earlier experiments [10, 11]. Charge-exchange for antihydrogen production was demonstrated by the ATRAP collaboration in 2004 [32] In this first demonstration Cs∗ atoms were used for positronium formation whereas - in the current experiments nanoporous silica targets are utilised. ASACUSA measures nuclear cross sections of antiprotons [43] at low (< 100keV) energies which will not be covered here
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