Multi-Anode Photomultplier (MAPMT) readout for High Granularity Calorimeters

Hadron calorimeter high performance in jet sub-structure measurements can be achieved for objects with $p_{T}$ greater than 1 TeV if the readout geometry is finely segmented in $\Delta\eta \times \Delta\phi$. A feasibility study to increase the readout granularity of TileCal, the central hadron calorimeter of the ATLAS detector, is presented. We show a preliminary study exploring the possibility to increase by a factor 4 the present readout granularity of the inner layer cells of TileCal (0.1->0.025 in $\Delta\eta$) and to split into two layers the intermediate section of TileCal. The proposed solution is designed to cope with mechanical and readout bandwidth and power constraints. Assuming that the mechanics of the Tile modules cannot be changed, Multi-Anode PMTs with same boundary geometry of the present single-anode PMTs are considered to readout WLS bers, ideally one per pixel, carrying the signals from the individual scintillating tiles of each detector cells. The discussed challenges of the design are: the new optics required to expand the image of WLS fiber bundle onto the MAPMT cathode; the procedure to map the individual tile luminous signal in the individual anode signal; the architecture of the new front end electronics for summing and digitizing the MAPMT signals.