Parapositronium Decay Research Articles

The OZI rule violating radiative decays of the heavy pseudoscalars

In lowest order of QCD, the rates for radiative transitions violating the OZI rule of heavy pseudoscalars are found to be extremely small. The η c → γ + ϱ, ω, ϕ width is predicted two orders of magnitude below present experimental bounds on X(2.8) → γ+ π + π −. As a by product, we get for the 4 γ parapositronium decay width Γ= m e α 7 · 1.352 X 10 −2.

Effective electron density for free-positron annihilation in low-Z compounds

Time spectra of positrons annihilating in various low-Z compounds, mostly liquids at room temperature, were investigated. They can be consistently resolved into three components which can be ascribed to the ortho- and para-positronium decay and to the annihilation of free positrons. The lifetime of this last component is interpreted in terms of Dirac’s formula and it is shown that each atom contributes to the decay rate with an amount typical of the atom itself,i.e. independent of the structural properties of the molecule and of the material. For H, Li, B, C, O, Cl the number of effective electrons per atom is obtained.

Fine structure in the delayed coincidence lifetime curves for positrons in argon

The lifetimes of positrons in argon and argon-nitrogen mixtures have been measured in more than one hundred experiments. With a high-resolution time-to-pulse-height converter the `shoulder' after the prompt peak has been studied. The results are interpreted to mean that (i) the τ2 component is due to the decay of orthopositronium, (ii) the shoulder is that part of the τ1 component arising from the decay of free positrons with energies below the Ore gap and (iii) the prompt peak includes the decay of parapositronium, positronium in excited states and metastable collision complexes, for example Are+, formed from positrons with energies higher than the threshold of the Ore gap.