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"Development of a silicon-tungsten test module for an electromagnetic calorimeter"

We are interested in designing, contructing, and testing the fundamental building blocks for a sampling ECal with tungsten radiator and highly segmented silicon readout which could be practical for a real detector. Our design features a readout chip which is fully integrated with the silicon detectors. This allows the design to naturally achieve a high transverse segmentation (currently 3.5 mm) while maintaining a small readout gap (1 mm) so as not to degrade the small Moliere radius of tungsten. These two properties (segmentation and Moliere radius) are the two most important properties for an electromagnetic calorimeter of a detector concept which employs particle flow algorithms, such as SiD or LDC. The integration of the electronics makes our project unique and provides improved particle flow capabilities relative to more conventional designs. Our R&D also points to the favorable scalability of the integrated approach in terms of cost and thermal management (we only require passive cooling).

The basic elements of the design consist of 15 cm silicon detectors with 1024 detector pixels and 1024-channel ASIC readout chips (called KPiX -- see attached talk by Breidenbach). The chips are bump bonded to the detectors. The KPiX chip performs the analog conditioning and full 15-bit digitization for all channels, taking into account the timing characteristics of the (superconductor-based) LC. The data are serialized for relatively simple transport to the readout using light cables within the 1 mm readout gaps. It is worth noting that KPiX could also be readily adapted for use with silicon trackers or hadronic calorimeter detectors at the LC.

The goal of our R&D is to fabricate a full-depth electromagnetic calorimeter prototype module. This nominally consists of 30 longitudinal layers, each consisting of a 15 cm detector outfitted with a KPiX chip sandwiched between 2.5 mm thick tungsten radiator layers. The full prototypes are necessary to study and understand hadron showers in finely segmented calorimetry in order to validate the simulations employed in particle flow, which in turn are used to optimize the overall detector design. Our ECal module would first be fully characterized for electromagnetic response and resolution in an electron beam, probably at SLAC in 2007.

We have purchased a first round of 10 15-cm detectors, which include the full metallizations necessary for the KPiX chip. These have been fully characterized in the lab (Oregon) -- see the attached talk by Strom. The KPiX chip has been fully designed (SLAC) and the first prototypes have been fabricated and will be evaluated in the first months of 2006. Meanwhile, the light cable is being designed and preparations for bump bonding are underway (Davis). The purchase of silicon detectors for the full module will require funding beyond that which can be expected from the LCDRD process.