Development of double SiPM readout method for ILD scintillator electro-magnetic calorimeter

The electro-magnetic calorimeter concept using plastic scintillator (Sc-ECAL) is being developed for detectors at future electron-positron colliders such as ILC . The Sc-ECAL is based on $5\times 45\times 2{\text{ mm}}^3$ plastic scintillator strips readout by SiPMs. This can realize a virtual $5\times 5{\text{ mm}}^2$ cell segmentation which is required for particle flow calorimetry at ILC detectors. However, there are some issues such as signal/noise ratio and ghost hits. A scintillator strip design based on double SiPM readout is being developed where a twice longer strip ($5\times 90\times 2{\text{ mm}}^3$) is read out by two SiPMs, one at each end. The performance of Sc-ECAL can be improved in various aspects by this method. The performance of the double SiPM readout was tested with a prototype setup. The position dependence of the light yield for a 90 mm-long scintillator strip was measured. A higher light yield and reasonably uniform response were observed with the sum of the two SiPM readouts. The hit position was reconstructed by using the charge and time difference between the two readouts. A position resolution of 20 mm was obtained.