Photodetector R&D for the belle II upgraded forward electromagnetic calorimeter

Abstract

The Belle II experiment will operate at the SuperKEKB e+e- collider, designed to reach a peak luminosity of 8×1035 cm-2s-1 at the Γ(4S) resonance. The high background environment of SuperKEKB poses serious challenges to the design of the Belle II detector. In particular, an upgrade of the forward Electromagnetic Calorimeter is foreseen: the new calorimeter will use pure CsI crystals, which have a faster scintillation light emission and lower light yield than the CsI(Tl) crystals presently used. An intense R&D program is ongoing to select the optimal photodetector to meet the stringent requirements set by the use of pure CsI in Belle II. A study of equivalent noise, resolution, radiation hardness and stability of low noise, high-gain avalanche photodiodes obtained by reading single pure CsI crystals is discussed. Our preliminary results indicate that a readout chain using these devices meets the requirements on electronic noise set by the Belle II simulation and could represent a cost-effective choice for the readout of pure CsI crystals in general.