parapositronium


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parapositronium

[¦par·ə‚päz·ə′trō·nē·əm]
(particle physics)
The state of positronium in which the positron and electron have antiparallel spins.
References in periodicals archive ?
There are two kinds of positronium: parapositronium p-Ps, in which the spins of the electron and the positron are oppositely directed so that the total spin is zero, and orthopositronium o-Ps, in which the spins are codirected so that the total spin is one.
Other positrons capture electrons from gas atoms thus producing orthopositronium and parapositronium (in ratio 3:1).
This method is quite justified and is commonly used, because the life span of excited [sup.22*]Ne is as small as [tau] [??] 4 x [10.sup.-12] s, which is a few orders of magnitude less than those of the positron and parapositronium.
The yield of positronium ([I.sub.2]) and the parameters of its annihilation at the passage through organic liquids were measured by two techniques: either angular (parapositronium) or temporal (orthopositronium) correlations of annihilation quanta were registered.
There are two kinds of that: parapositronium [sup.S]Ps, in which the spins of electron and positron are oppositely directed and the summary spin is zero, and orthopositronium [sup.T]Ps, in which the spins are co-directed and the summary spin is one.
In the same year Glashow [45] gave further development to the idea and showed that in case of 3-photon annihilation [sup.T]Ps will "mix up" with its mirror twin thus producing two effects: (1) higher annihilation rate due to additional mode of decay [sup.T]Ps [arrow right] nothing, because products of decay passed into the mirror Universe can not be detected; (2) the ratio between orthopositronium and parapositronium numbers will decrease from [sup.T]Ps : [sup.S]Ps = 3:1 to 1.5 : 1.