Recent developments of the SDHCAL prototype

Abstract

After the construction and successful operation of the first technological prototype of the Semi-Digital Hadronic CALorimeter (SDHCAL), developed within the CALICE collaboration, new R{\&}D efforts have been initiated to fully validate the SDHCAL option for future experiments proposed for the ILC and CEPC colliders. The SDHCAL is a sampling hadronic calorimeter using large Glass Resistive Plate Chamber (GRPC) as active medium with embedded readout electronics. The GRPC prototype size is 1~m$^2$ while future detectors require GRPC detectors with scalable length up to 3~m long (0.9$\times$3~m$^2$). The readout Printed Circuit Board (PCB) consists of 1~cm$^2$ copper pads on one side and 64-channel HARDROC readout chips on the other side. The design of such large size scalable detectors has been addressed and has required rethinking the gas flow in the GRPC in order to maintain detection efficiency and spatial response homogeneity. The readout PCB was also redesigned to make it scalable in length and more tolerant of ASIC readout failures. It now uses the latest version of the HARDROC readout chips series. To deal with the maximum production size of a PCB with 8 layers, an ingenious scheme with several PCBs connected to each other by tiny, flexible connectors has been developped. A new DAQ interface board with an optimized geometry to fit the requirements of the ILD detector, can handle a PCB area up to 2.76~m$^2$, sufficient to cope with the GRPC maximum size in ILD. A new cassette, as part of the calorimeter absorber, is being designed. The main challenge is to ensure the rigidity and uniform contact between the GRPC and its PCB. For the ILC detector, the ILC beam time structure is used to power-pulse the ASICs to keep the power consumption low enough to avoid cooling the PCB. For the CEPC, the continuous operation of the accelerator implies adding cooling capacity to the designed cassette structures. In addition, tools to handle the new cassette are being finalized. Finally, the way to manufacture the mechanical structure to support 3~m long GRPC with the needed improved flatness has been solved. A first fully assembled prototype of 2~m$^2$ with 4 GRPCs is expected to be ready in year 2022. In addition, new developpements to replace single gap GRPC by multigap GRPC coupled with fast timing electronics are being pursued. A time resolution better than 50 ps is achievable. This will allow to follow the temporal evolution of the hadronic showers developing in the calorimeter. In parallel, the first SDHCAL prototype has been extensively tested in beam test facilities. Refined analysis techniques are being developed to improve the energy and shower reconstruction. The latest analysis developments cover techniques to improve the spatial uniformity of the response and a better treatment of the particle incidence angle in the energy reconstruction.