Test of prototype electromagnetic calorimeter (FOCAL) using large dynamic range ASIC ANUINDRA at CERN-SPS

A new sampling type electromagnetic calorimeter, FOrward CALorimeter (FOCAL), has been proposed for the ALICE experiment at CERN to boost its physics capabilities in the forward pseudorapidity region (2.5≤η≤5.5). A detailed GEANT-4 simulation was perfomed and an optimised geometry, with depth 20 XR and transverse size with inner and outer radii of 6 cm and 80 cm respectively, at 8 m away from the interaction point was obtained. The absorber/ convertor and the detector were chosen to be Tungsten and Silicon repectively, to confine and tighten the electromagnetic showers along the longitudinal and transverse directions for better energy and position resolutions in the desired energy range (1–200 GeV). The calorimeter has longitudinal segmentation with 20 layers, each consisting of 1 XR thick W and 300 μm Si pad sensors followed by associated electronics. Also, for better position resolution, 3 pixelised (1 mm) Si-sensor layers were used along with comparatively coarse segmentation for the other layers (1 cm). A series of prototype detectors were fabricated and tested both with radioactive source and test beam to check the feasibility and functionality of the calorimeter. Initially, a miniprototype was constructed and experimented at the CERN-PS using MANAS as the readout electronics [1]. A linear relationship between simulation and experimental results ensured satisfactory performance of the mini-tower. Following the successful test, a full-depth (20 XR) FOCAL prototype was designed, developed and tested at CERN-SPS beam line using MANAS and ANUSANSKAR as the readout ASICs, whose details have been presented at the DAE Symp. On Nucl. Phys, 2016 [2]. Both the prototypes were tested with pions to study MIPresponse and electrons (EM-shower) of different incident energies starting from 1 GeV to 60 GeV. Analysis shows performance of the prototype getting affected (saturation in ADC distribution) because of limited dynamic range (upto 600 fC) of the ASICs used. Thus, a new ASIC, ANUINDRA with large dynamic range (~ 2.6 pC) has been designed to overcome the saturation in data taking for higher energies. This ASIC has been tested in the laboratory as well as with the full-depth prototype at the SPS beam line facility at CERN.