About the Cover

Vol. 96 No. 10 (2020)

Physics with cold antimatter has been rapidly growing in the last 20 years and having significant overlap with the period of the Antiproton Decelerator (AD) at CERN. The major subjects of the field are the precise comparisons of the fundamental properties of matter-antimatter conjugates, which provide sensitive tests of charge–parity–time (CPT) invariance, an important symmetry that rests on basic assumptions of the Standard Model of particle physics, and stringent tests of the Weak Equivalence Principle (WEP). Both tests may also find a clue to solve the mystery of the matter-antimatter asymmetry of the universe.
To attack the problem, various groundbreaking techniques have been developed and are still in progress such as to cool antiprotons and positrons to extremely low temperatures, to manipulate antihydrogen atoms, to construct ultra-high-precision Penning traps, etc. The cover figure (right) shows a summary of the latest results of CPT symmetry tests on the energy scale including laser spectroscopy of antihydrogen as well as the magnetic moment and charge-to-mass ratio measurements of antiproton and proton, as they are discussed in the review article by Dr. Yasunori Yamazaki within this volume.
Former research results including the K0 and K0 mass difference, used to be the best CPT symmetry test, is also shown for comparison. Bar's right and left ends correspond to the energy of the measured quantity and the difference of the matter and antimatter in energy scale, respectively. Laser spectroscopy of antiprotonic helium has also been advanced a lot improving its precision.
An additional new decelerator, the Extra Low ENergy Antiproton ring (ELENA), has been constructed and will start its operation in 2021 (cover figure, left). ELENA will provide 10-100 times more cold antiprotons to each experiment, which will open a new and prosperous era of the cold antimatter physics soon.

Klaus Blaum
Director at the Max-Planck-Institute for Nuclear Physics, Heidelberg (Germany), and Vice President for the Chemistry, Physics and Technology Section of the Max-Planck-Society.