Search for short-lived axions in a nuclear isoscalar transition

Axions, if existing, can cause a strong signal of positron-electron pairs in isoscalar M1 transitions in competition with gamma-ray emission. We searched for such a signal in the 3.59 MeV transition in 10B with a fourfold Mini-Orange spectrometer. No axion events were found within two percent of the prediction for the standard axion- to γ-ray branching ratio

Lepton pairs from a forbidden M0 transition:Signaling an elusive light neutral boson?

Electron-positron pairs have been observed in the 10.95 MeV 0(-) -> 0(+) decay in O-16. This magnetic monopole (M0) transition cannot proceed by gamma-ray decay and is, to first order, forbidden for internal pair creation. However, the transition may also proceed by the emission of a light neutral 0(-) or 1(+) boson, which might play a role in the current quest for light dark matter in the Universe

Search for a short-lived neutral boson with a mass around 9 MeV/c(2)

Data on internal pair conversion in some high energy magnetic nuclear transitions exhibit an excess in e(+)e(-) pairs around 9 MeV/c(2) invariant mass. While the deviations individually may be circumstantial, in combination they appear to point to a common anomaly, which can be explained to the emission of a short-lived isoscalar pseudoscalar neutral boson

A multi-detector array for high energy nuclear e(+)e(-) pair spectroscopy

A multi-detector array has been constructed for the simultaneous measurement of energy and angular correlation of electron-positron pairs produced in internal pair conversion (IPC) of nuclear transitions up to 18 MeV. The response functions of the individual detectors have been measured with mono-energetic beams of electrons. Experimental results obtained with 1.6 MeV protons on targets containing B-11 and F-19 show clear IPC over a wide angular range. A comparison with GEANT simulations demonstrates that angular correlations of e(+)e(-) pairs of transitions in the energy range between 6 and 18 MeV can be determined with sufficient resolution and efficiency to search for deviations from IPC due to the creation and subsequent decay into e(+)e(-) of a hypothetical short-lived neutral boson