A novel detection system for laser cooling of ortho-positronium

We report on the development of a position-sensitive scintillation detector system for viewing laser-cooled ortho-positronium (oPs) annihilation points. Ortho-positronium can be cooled down to a recoil limit of 0.1 K by an ultraviolet laser in spite of its relatively short lifetime. In order to perform this experiment the wavelength of Cr:LiSAF laser is considered to be 243 nm which corresponds to the transition energy of 1S–2P states of oPs. Thermal positronium plays an important role in laser cooling of oPs. We investigated various kinds and sizes of inorganic scintillators. Position resolutions of YAP:Ce and CsI(Tl), respectively, were determined to be 3.00 and 3.8 mm. Extensive Monte Carlo simulation studies were performed to view the decay positions of oPs using the time-of-flight method. Related issues of position resolution measurements and oPs decaying points will be discussed.