ANTIMATTER MATTERS: RECENT PROGRESS WITH COLD ANTIHYDROGEN AND ANTIPROTON

ABSTRACT:

Antihydrogen, the opposite number of hydrogen, is the simplest antimatter. At the same time, antihydrogen is stable in vacuum, which guarantees a long observation time for high precision spectroscopy.  A comparison of the spectroscopic properties with those of hydrogen constitutes a stringent test of the CPT symmetry, the most fundamental law of physics.

Recently, experimentalists working on cold antihydrogen have achieved two new progresses. One is the trapping of antihydrogen atoms in a magnetic bottle consisting of an octupole magnet and a pair of mirror coils [1]. Considering the bottle depth, the trapped antihydrogen atoms were really cold, less than 0.7K. The other is a successful synthesis of antihydrogen atoms in a so-called cusp trap [2], where an anti-Helmholtz coil configuration is employed. In this case, the magnetic field has axial symmetry, and thus allows extracting antihydrogen atoms in a field-free region as an intensified and at the same time spin-polarized beam, which is the ultimate condition to realize high resolution spectroscopy. With these two major progresses, the field of cold antimatter research is now ready to start real physics experiment such as high precision laser spectroscopy of 1S-2S transition and microwave spectroscopy of ground state hyperfine transitions. Further, a spin-flip of an isolated proton has recently been successfully observed [3]. Considering the fact that exactly the same setup can be used for antiproton, the spin-flip experiment will become one of the most important players for the CPT symmetry test. 

References
[1] G. B. Andresen et al., Nature 468 (2010) 673, and M. Fujiwara et al, Nature Phys. 7(2011)558
[2] Y. Enomoto et al., Phys. Rev. Lett. 105 (2010)243401.
[3] S. Ulmer et al., Phys. Rev. Lett. 106 (2011) 253001