Experiment with the source  

Invisible decay search of orthopositronium with the source experiment

The main components of the detector are:

  1. the positron source (22Na),
  2.  the positron tagging system,
  3.  the positronium formation SiO2 target ,
  4. 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 2
g 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.



Last update:  P. Crivelli - Nov. 13 2004