Abstract
Antihydrogen, the bound state of an antiproton and a positron, is of interest for use in precision tests of nature's fundamental symmetries. Antihydrogen formed by carefully merging cold plasmas of positrons and antiprotons has recently been trapped in magnetic traps. The efficiency of trapping is strongly dependent on the temperature of the nascent antihydrogen, which, to be trapped, must have a kinetic energy less than the trap depth of . In the conditions in the ALPHA experiment, the antihydrogen temperature seems dominated by the temperature of the positron plasma used for the synthesis. Cold positrons are therefore of paramount interest in that experiment. In this paper, we propose an alternative route to make ultra-cold positrons for enhanced antihydrogen trapping. We investigate theoretically how to extend previously successful sympathetic cooling of positrons by laser-cooled positive ions to be used for antihydrogen trapping. Using simulations, we investigate the effectiveness of such cooling in conditions similar to those in ALPHA, and discuss how the formation process and the nascent antihydrogen may be influenced by the presence of positive ions. We argue that this technique is a viable alternative to methods such as evaporative and adiabatic cooling, and may overcome limitations faced by these. Ultra-cold positrons, once available, may also be of interest for a range of other applications.
Highlights
Antihydrogen, the bound state of an antiproton and a positron, holds the promise of unprecedented precision in the study of matter–antimatter symmetry in nature
We have presented a novel technique for enhanced antihydrogen trapping for precision experiments with cold antihydrogen
The technique expands on demonstration experiments at NIST from the turn of the century using laser-cooled ions to sympathetically cool the positron plasma used in several antihydrogen experiments
Summary
Antihydrogen, the bound state of an antiproton and a positron, holds the promise of unprecedented precision in the study of matter–antimatter symmetry in nature. In the autoresonance-based scheme used by ALPHA for successful trapping, the antihydrogen seems to be formed at or close to the temperature of the positron plasma, i.e. the antiprotons reach thermal equilibrium with the positron plasma before forming antihydrogen [2] This is consistent with calculated equilibration rates of ∼200 Hz for typical experimental parameters in ALPHA [9]. Additional, active cooling, may combat these various heating sources, and potentially make the positrons colder than the surroundings Two such methods have been demonstrated to work for large numbers of particles in plasmas composed of electrons (e−), positrons or antiprotons. The first is that positrons are strongly interacting with the surroundings through their cyclotron motion, and constant efficient cooling is needed to maintain low temperatures This is difficult, if not impossible, to achieve with either of the two methods. With typical numbers of cooling ions at about 10% of the number of positrons, the combination of centrifugal separation of the ions and positrons and the injection of antiprotons predominantly on axis reduce the influence of this process to negligible levels
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
