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"Digital Hadron Calorimetry using Gas Electron Multiplier Technology"

We have been developing the implemaentation of digital hadron calorimetry for a future Linear Collider detector using Gas Electron Multiplier technology. This is a critical and essential development for future experiments that will rely on the Particle Flow Algorithm approach to achieve unprecedentedly precise jet energy and jet-jet mass resolutions. This level of performance is required to separate w and Z bosons and Higgs particles in their hadronic decay modes on an event-by-event basis. The digital approach relies on a fine transverse and longitudinal segmentation of the calorimeter and a linear relation between digital "hits" and energy. The energies of charged particle clusters are taken from the momentum measurement in the tracking system once the track/cluster associations have been made. The residual neutral hadron energy is maesured using the digital information.

In the GEM approach, the ionization electrons released in the drift region of an active layer of the sampling calorimeter are amplified by using two successive GEM foils (double-GEM). The amplified charge is collected at the anode, or readout pad, layer which is at ground potential. This layer is subdivided into 1cm x 1cm pads needed to implement the digital approach.

We have built several 10cm x 10cm double-GEM prototypes using foils from CERN. We have measured the gain, efficiency, hit multiplicity, using sources and cosmic rays, for a variety of Argon-CO2 gas mixtures. We have demonstrated the viability of our approach with these results. We have also been developing large (1m x 30cm) mechanical modules to test production procedures. Working with 3M Corporation in Texas we have produced larger (30cm x 30cm) GEM foils. We shall use these to build the next, medium scale, prototype system, which will have five double-GEM chambers. In the longer term, we are developing plans to construct a full scale meter-cubed, 40-layer prototype for exposure in a test beam at Fermilab in 1-2 years timeframe.

We have been supported by the US DOE ADR and LCRD programs. While this has enabled us to develop and test initial prototypes, the current level of funding is significantly below that required to build and test a full scale hadron calorimeter module. It is critical that sufficient support is forthcoming to allow this module to be built and tested to verify the performance of this combination of technology and its accurate, detailed simulation using GEANT4. This is an essential precursor to the inclusion of this approach in any viable ILC detector proposal.
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