On the formation of trappable antihydrogen

Abstract

The formation of antihydrogen atoms from antiprotons injected into a positron plasma is simulated, focussing on the fraction that fulfil the conditions necessary for confinement of anti-atoms in a magnetic minimum trap. Trapping fractions of around 10 −4 are found under conditions similar to those used in recent experiments, and in reasonable accord with their results. We have studied the behaviour of the trapped fraction at various positron plasma densities and temperatures and found that collisional effects play a beneficial role via a redistribution of the antihydrogen magnetic moment, allowing enhancements of the yield of low-field seeking states that are amenable to trapping.

Sympathetic cooling of positrons to cryogenic temperatures for antihydrogen production

“…1 ). Experimental and theoretical evidence 13 , 14 suggests that in the parameter range of current experiments, as opposed to previous ones 15 , antiprotons tend to thermally equilibrate with the positrons before antihydrogen is formed during this merging. A consequence is that the temperature of the nascent antihydrogen will be that of the positron plasma.…”

On the binding energies of antihydrogen formed by the interactions of antiprotons in cold positron plasmas

“…The p trajectories were initialised from a thermal distribution at T e with the e + plasma taken, for simplicity, as an infinitely long cylinder of 1 mm radius. This approximation does not affect the outcome of the simulation, as detailed elsewhere [20]. In that work, the fraction of the formed H which was deemed to be trappable was deduced by applying several criteria.…”

“…Since the relevant dynamics for anti-atom formation occurs on scales on order of magnitude shorter than Debye-length we do not expect significant changes, though we cannot rule out that at our lowest temperatures and largest density some correction due to this effect could occur. The fraction of p s resulting in H which survives this treatment was referred to as the H-fraction, f H, in [20], and it is from this ensemble that the data we present in section 3 is drawn. We note, following [20], that radiative de-excitation processes (which will eventually lead to H in the ground state) are not included, as these are not important during the first stages of H formation [31,32] considered here.…”

“…The fraction of p s resulting in H which survives this treatment was referred to as the H-fraction, f H, in [20], and it is from this ensemble that the data we present in section 3 is drawn. We note, following [20], that radiative de-excitation processes (which will eventually lead to H in the ground state) are not included, as these are not important during the first stages of H formation [31,32] considered here.…”

Formation of antihydrogen beams from positron–antiproton interactions

“…Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. this radial transport for the number of trappable H atoms generated in an experimental situation typical of ALPHA or ATRAP [15]. The purpose of the present paper is to investigate how the radial transport affects the number of beam-like H s generated from three-body combination of antiprotons injected in a positron plasma.…”