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Experiment
with the source
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Invisible decay search of orthopositronium with the source experiment
The main components of the detector are:
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the positron source (22Na),
- the positron tagging
system,
- the positronium formation
SiO2 target ,
- a hermetic 4p-detector
The coincidence of the PM signals from the positrons crossing the fiber, opens the gate for the data acquisition (DAQ). In the
off-line analysis the 1.27 MeV photon, which is emitted from the source simultaneously with the positron, is required to be in the trigger BGO counter (shown in Fig.2) resulting in a high confidence level of positron appearence in the positronium formation region. A positron, which enters the
SiO2 target may capture an electron creating positronium. The calorimeter detects, either the direct
2g annihilation in flight or the 2(3) photons from the para
(ortho)-positronium decays in the target.
The occurence of the o-Ps &rarr invisible decay would appear as an excess of events with zero-energy deposition in the calorimeter above those expected from the Monte Carlo prediction or from the direct background measurement.
The Monte Carlo simulation used to design this detector in Geant 3 was tuned using our previous
search for a decay of orthopositronium in one gamma and two weak interactive massive
particles.