Absorption of Scintillation Light in a 100 $\ell$ Liquid Xenon$\gamma$ Ray Detector and Expected Detector Performance

An 800 ℓ liquid xenon scintillation γ ray detector is being developed for the MEG experiment which will search for µ + → e + γ decay at the Paul Scherrer Institut. Absorption of scintillation light of xenon by impurities might possibly limit the performance of such a detector. We used a 100 ℓ prototype with an active volume of 372 × 372 × 496 mm 3 to study the scintillation light absorption. We have developed a method to evaluate the light absorption, separately from elastic scattering of light, by measuring cosmic rays and α sources. By using a suitable purification technique, an absorption length longer than 100 cm has been achieved. The effects of the light absorption on the energy resolution are estimated by Monte Carlo simulation.