Novel Si sensors and readout for the compact high resolving power electromagnetic calorimeter

Calorimetry is the most important single tool for electron, photon, and neutral pion measurements and still drives overall detector dimensions and cost. We report here on a development of a new Si detector with “integrated” readout which helps to keep calorimeter dimensions and cost under control simultaneously enhancing the multi-photon resolving power and implementing energy flow measurement capability in Si based calorimeter. The prototype electromagnetic Si-W calorimeter with high resolving power (FOCal) was recently built and tested ¹ with funding provided by PHENIX and is now being upgraded to combine precision position measurements with energy flow measuring functionality (StriPad and MiniPad-structured sensors in every sampling layer). New sensors are made in p+/n/n+ configuration with segmented side being the p+. All devices are read by the 128 channels SVX4 strip readout chip developed at FNAL. Depending on the sensor layout the 128 readout channels are either (1) shared between 16 pixelated pads (15×15 mm² each) overlapping with 112 pixelated strips (~0.54×62mm² each), or connected to (2) 128 strips (~0.47×62mm² each) or (3) 128 minipads (~1.8×15mm² each) implemented on a 62×62mm² silicon substrate. The sensors are laminated with readout cards which carry one or two (dual gain readout) SVX4 chips to form pluggable micromodules. Thus built micromodules take only 2 mm of longitudinal space in detector leading to dramatic improvement in detector compactness (small Moliere radius). Novel sensors supported by low power, high density fully digital readout allows to upgrade silicon based calorimeter for energy flow measurements at essentially no extra cost.