Ultra-low energy antihydrogen

Abstract

The study of CPT invariance with the highest achievable precision in all particle sectors is of fundamental importance for physics. Equally important is the question of the gravitational acceleration of antimatter.In recent years, impressive progress has been achieved at the Low-Energy Antiproton Ring (LEAR) at CERN in capturing antiprotons in specially designed Penning traps, in cooling them to energies of a few milli-electron volts, and storing them for hours in a small volume of space. Positrons have been accumulated in large numbers in similar traps, and low-energy positron or positronium beams have been generated. Finally, steady progress has been made in trapping and cooling neutral atoms. Thus the ingredients to form antihydrogen at rest are at hand. This report will describe the techniques available to produce, decelerate, and accumulate antiprotons at low energy, how to generate high-density plasmas of low-energy positrons, and how to combine these two species into antihydrogen.Once antihydrogen atoms have been formed, they can be captured in magnetic gradient traps and standard spectroscopic methods applied to interrogate their atomic structure with extremely high precision for comparison with the hydrogen atom. In particular, the 1S-2S transition, with a lifetime of the excited state of 122 ms and thereby a natural linewidth of five parts in 10 16 , offers in principle the possibility to directly compare matter and antimatter properties at a level of one part in 10 18 . Other quantities of interest, such as the hyperfine structure splitting of the ground state, will also be discussed.Finally, we will give a brief outlook into the future and comment on some of the possible antiproton facilities which could be used to continue this field of research well into the next century.

Stability of few-charge systems in quantum mechanics

“…See Amoretti et al [190]. This followed on from several years preparatory work by the ATHENA project (ApparaTus for High precision Experiments on Neutral Antimatter), Charlton et al [191] and Holzscheiter et al [192,193], and the competing ATRAP (Antihydrogen TRAP) project of Gabrielse et al [194]. The most recent results obtained by ATRAP are described by Gabrielse et al [195].…”

“…Also their masses and gyromagnetic ratios should be equal and their lifetimes should be the same. In addition, this symmetry predicts that H and H should have identical spectra [191,192,193,194]. Experimentalists plan to test, as far as possible, whether H and H do have these properties.…”

Real-time Detection of Antihydrogen Annihilations and Applications to Spectroscopy

“…Proposed mechanisms for releasing atoms undergoing 1S −2S transitions include photo-ionization of the 2S state by 243 nm photons [28] and the quench of the 2S state to the 2P state by means of an electric or microwave field, followed by a decay to a high-field-seeking state [29]. Antihydrogen 1S − 2S transitions are then signaled by a decrease of annihilation counts at the end of each trial.…”

“…[29]: the antihydrogen cloud is irradiated for approximately 10 ms, after which a short electric quench field is applied and a 10 ms detection window (determined by the drift time of released H atoms towards the trap wall) is opened to record any antihydrogen annihilation; the cycle is then repeated throughout the whole H confinement time. However, it should be noted that, if we estimate the electric field in the frame of the moving H atoms to be ∼ 1 V/cm, the decay rate of the 2S state would be approximately 3 kHz [32]; furthermore, 2S photo-ionization by a third photon could become, at higher power, a non-negligible loss mechanism.…”

“…These considerations suggest that the detection cycle proposed in Ref. [29] would be very inefficient.…”