Production of a Fully Spin-Polarized Ensemble of Positronium Atoms

Abstract

Long-lived |m|=1 positronium (Ps) atoms are produced in vacuum when high density bursts of positrons with net polarization p{0} are implanted into a porous silica film in a 2.3 T magnetic field. We observe a decrease in the |m|=1 population as the density of the incident positron beam is increased due to quenching interactions between oppositely polarized Ps atoms within the target. Saturation of this density dependent quenching indicates that the initial positron spin polarization p{0}=28+/-1%, and demonstrates the long term (10{2} s) survival of positron polarization in a Surko-type buffer gas trap. We conclude that, at high Ps densities, the minority spin component is essentially eliminated and the remaining Ps is almost entirely (approximately 96%) polarized, as required for the formation of a Ps Bose-Einstein condensate.

Positronium formation via excitonlike states on Si and Ge surfaces

“…The reason why the maximum yield in Fig 4 (a) is larger than that of Fig 4 (b) is that the higher magnetic field that is required for attaining a high positron density leads to magnetic quenching of positronium [68]. This effect, which will not affect f d after around 0.75 T [69], reduces the amount of long lived Ps present by mixing m = 0 triplet and singlet states [70]. However, increasing the magnetic field also increases the positron beam density, and the increased Ps yield due to e-h pair production partially compensates for the magnetic quenching, otherwise the difference in percent delayed fractions would be around 40 % [71,54].…”

Experimental progress in positronium laser physics

“…This approach provides a very clear signal (see Fig. 38), and can even be used to determine the spin polarization of the incident positron beam [362]. This is possible because CP violation in beta decay means that positrons produced from 22 Na sources are intrinsically spin polarized [590,591].…”

“…This is possible because CP violation in beta decay means that positrons produced from 22 Na sources are intrinsically spin polarized [590,591]. This polarization is not lost in moderation [592] or trapping processes [362], and carries over to the Ps, meaning that there will be an asymmetry in the fraction of m = ±1 states produced. Increasing the Ps density to the point where Ps-Ps scattering can occur will lead to losses via SEQ or Ps 2 molecule formation, but eventually the minority spin component will be exhausted, after which there will be The solid line is a fit to a model that includes a density-dependent PsPs induced decay rate.…”

“…The modified Ps dynamics resulting from such quantum confinement [290] can be advantageous in studies of Ps-Ps interactions [287,288,362] . Observed shift and narrowing of the 1 3 S1-2 3 PJ transition inside a mesoporous network.…”

“…As discussed elsewhere [328], both of these materials can be used for SSPALS measurements. PWO is less efficient in terms of light production (a few percent of NaI) [359] and has a decay time of around 10 ns, which makes it well suited for very high intensity pulses, as are required for Ps-Ps scattering or Ps 2 formation experiments [119,[360][361][362]. LYSO has a high density (8 g cm −3 ), a high light output (∼75% of NaI), and a decay time of ≈40 ns.…”