Evidence for peak structure in e++ Th interactions

doi:10.1016/0370-2693(86)91253-0

Physics Letters B

Volume 181, Issues 1–2, 27 November 1986, Pages 52-56

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Abstract

Thorium and tantalum targets were bombarded with positrons from a radioactive source having an endpoint energy of 1.9 MeV. Electron and positron kinetic energy were measured in coincidence using mini-orange magnetic spectrometers. Evidence for peak structure at 340 keV was found in the spectra from the thorium target, and is discussed in the context of peaks observed near this energy in collisions of high-Z nuclei.

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Nuclear data sheets for A = 181
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The nuclear structure and the decay data for all the isobars of A = 181 are presented in this evaluation. New levels of ¹⁸¹Hf were studied by (n,γ), (pol d, p), (d, pγ) and (²³⁸U,²³⁷U'γ) reactions. New levels of ¹⁸¹Ta were studied by (p,nγ), (p, d), Coulomb excitation and heavy ion reactions. Heavy ion reactions added information to high spin states of ¹⁸¹Re, ¹⁸¹Os and ¹⁸¹Ir. In addition, ¹⁸¹Hg and ¹⁸¹Tl structures are also studied by α–decay experiments. The present evaluation supersedes the earlier one on A = 181 by R.B. Firestone (1991Fi01), published in Nuclear Data Sheets 62, 101 (1991), and the ones on ¹⁸¹Pt, ¹⁸¹Au and ¹⁸¹Hg, by C.M. Baglin, published in Nuclear Data Sheets 87, 197 (1999), 87, 225 (1999) and 87, 239 (1999).
Search for correlated two-photon emission from e+(82Sr) + Th interactions
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A previously observed electron line at INS at 330.3±0.4 keV in e⁺+Th interactions has been implied by these authors to originate from the decay of an unknown neutral object X⁰. QED predicts a two-photon decay mode of X⁰ leading to a correlated two-photon coincidence peak at 841.3±0.4 keV. To search for such a peak γγ-coincidence experiments were performed. From an observed peak-like structure in the spectrum at 841.7±0.3 keV and an associated cross section of 10.6±3.1 (stat) ± 6.9 (syst) μb an upper limit for the cross section of 15.2±1.5 (syst) μb for the production and 2γ decay of the X⁰ was deduced with a statistical confidence level of 95%.
The C(Q<inf>0</inf>?) Scenario: Bound Sharp Positron decay, its resonant inverse, and Sharp lines from [β+ + atom]
1995, Nuclear Physics, Section A
The Composite Particle (Q₀?) Scenario is a phenomenology for the “(e⁺e⁻) Puzzle”. It implies a new “Supercomposite” molecule, the neutral C(Q₀?) particle bound to a nuclear ion. From such a molecule a C(Q₀?) particle may decay by the process of Sharp Annihilative Positron Emission: the e⁻ is captured into a Bohr orbit and only a single energetic e⁺ emerges. The inverse is Recoilless Resonant Positron Absorption which can encompass the sharp electron lines observed in β⁺ irradiation of heavy atoms within the same scenario. Thus emerges the expanded “Sharp Lepton Problem”, accessible experimentally via both β⁺ irradiation and high-Z heavy ion collisions. (By Occam's razor we here assume that the particle is in fact Quadronium: Q₀ = (e⁺e⁺e⁻e⁻).)
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The K-matrix for electron-positron scattering is evaluated in the 0⁺ channel for each of three relativistic wave equations derived from QED. When all the transverse single-photon-exchange contributions are treated we obtain zero width resonances or continuum bound states at mass values of 1.351, 1.498, 1.659, 1.830, 2.009, and 2.195 MeV. We assume that neglected processes are not crucial to the complete problem and therefore we compare these results with electron-positron coincidence peaks found in heavy ion experiments performed at GSI. We suggest additional types of experiments to search for these resonances.
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1989, Nuclear Inst. and Methods in Physics Research, A
A series of investigations on Bhabha scattering has been carried out in the last two years, searching for possible neutral resonances in the invariant mass range between 1.5 and 1.9 MeV/c², as motivated by the heavy-ion experiments at GSI. The currently highest sensitivity has been achieved by an experiment performed at ILL using the BILL β spectrometer to produce monoenergetic positrons and a high-resolution multidetector device. With systematic and statistical uncertainties of less than 0.25%, no evidence for any resonance was found around 1.8 MeV/c². The 97%-confidence upper limit on the intrinsic width and lifetime of a hypothetical spinless resonance is 1.9 meV and 3.5 × 10⁻¹³ s, respectively, establishing the most stringent bound for new particles in this mass region.

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¹: Present address: National Science Foundation, Washington, DC 20550, USA.

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Physics Letters B

Abstract

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Z. Phys. A

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Nuclear data sheets for A = 181

Search for correlated two-photon emission from e<sup>+</sup>(<sup>82</sup>Sr) + Th interactions

The C(Q<inf>0</inf>?) Scenario: Bound Sharp Positron decay, its resonant inverse, and Sharp lines from [β<sup>+</sup> + atom]

Electron-positron scattering resonances from relativistic two-body wave equations

A search for correlated e<sup>+</sup>e<sup>-</sup> pairs in the decay of <sup>241</sup>Am

Search for resonant Bhabha scattering at MeV energies