Design and Prototyping of a Scintillator-based
Semi-Digital Hadron Calorimeter
The NIU team has been investigating a finely-segmented scintillator-based hadron calorimeter for some time now. This option capitalizes on the marriage of proven detection techniques with novel photodetector devices. Absence of fluids/gases and very high voltages inside the detector aids longevity and operational stability.
The main challenge for a scintillator-based hadron calorimeter is the architecture and cost of converting light, from a large number of channels, to electrical signal. Our studies demonstrate that small cells (6-10 ) with embedded Silicon Photomultipliers (SiPMs)/Metal Resistive Semiconductor (MRS) photodetectors offer the most promise in tackling this issue. The in situ use of these photodetectors opens the doors to integration of the full readout chain to an extent that makes a multi-million channel scintillator calorimeter entirely plausible. Also, in large quantities the devices are expected to cost a few dollars per channel making the construction of a full-scale detector instrumented with these photo-diodes financially feasible.
The very large number of readout channels can still pose a significant challenge in the form of complexity and cost of signal processing and data acquisition. Reducing the dynamic range of the readout is a potential solution. Monte Carlo studies have shown that this is indeed a promising possibility as scintillator cells with an area in the 6-10 range are good candidates for one (digital) or two-bit (semi-digital) readout (see Fig. 1) where the lowest threshold is set so as to detect the passage of a minimum ionizing particle. Performance of PFAs on scintillator hadron calorimeter Monte Carlo's with a minimum of amplitude information in the form of thresholds also looks very competitive . Thus fabrication of cheap and compact electronics with just a few thresholds (three in the case of a 2-bit readout) which will deliver the required performance is a realistic possibility for a scintillator hadron calorimeter.
In these tasks we have been coordinating our efforts with European groups pursuing similar interests. This interaction takes place under the umbrella of the CALICE collaboration  which bands together universities and labs, interested in developing calorimeters for the Linear Collider, from all over the world. We are the only group in the United States, actively investigating the promising option of a scintillator-based hadron calorimeter.
Figure: Single hadron energy resolution as a function of the incident energy.