Study on Granularity Optimization for ILD Hadron Calorimeter

The CALICE Analogue Hadron CALorimeter (AHCAL) at the International Linear Collider (ILC) is a high-granularity hadron calorimeter based on scintillator tiles readout by MPPCs. Toward the construction of ILC, the AHCAL granularity is being optimized. We have studied mixed configurations of the granularity by using larger scintillator tiles. We first measured the performance of 60 × 60 mm$^2$ tile, which is larger than the standard 30 × 30 mm$^2$ tile. The uniformity of the response in the tile was found to be quite good although the light yield is reduced by a factor of two compared to the standard 30 × 30 mm$^2$ tile, which can be recovered with a larger-area MPPC. A prototype detection layer composed of 144 pieces of 60 × 60 mm$^2$ tiles was constructed. The detection layer was added to the AHCAL large technological prototype composed of 38 detection layers with 30 × 30 mm$^2$ tiles. The detection layer was successfully tested in test beam experiments at CERN SPS. The measured performance of the detection layer is presented as well as the study on the possible saturation using the test beam data.