Results of Prior Research

Members of NIU, ANL, SLAC, and UTA began collaborating on PFAs, simulations, and software development efforts in January, 2002. Several other groups have since joined the effort, and links have been established with European colleagues who had been active in this area already. The re sults that emerged through discussions at our regularly scheduled meetings have been presented at the Calor conferences, ECFA and ACFA meetings, the American LC workshops, and at the International LC Physics and Detector Workshops.

Toward the optimization of the HCal design, the NIU and ANL teams have started investigating both analog (cell energy measurements) and digital (hit density measurements) methods as functions of the cell size. Our preliminary findings suggest that with sufficiently small cells, the digital method yields a more precise measurement of the hadron energy, i.e., fluctuations in hit density are smaller than those in the sampled energy of a hadronic shower. Use of local hit density in lieu of the deposited energy to weigh the calorimeter hits results in superior energy resolution and lateral containment of single hadron showers. Two independent approaches to the implementation of a PFA have helped improve our understanding of the optimal cell sizes and geometry for best charged/neutral hadron shower separation in jets within the context of some specific overall detector parameters.

We will now briefly summarize our HCal optimization and algorithm development efforts. The HCal must be optimized to achieve, with due consideration of costs, benefits, and risks, the best balance between the reconstruction and energy resolution of neutral-hadron-initiated clusters in a jet, and the ability to separate them from the charged components. This is intimately related to the first step in the development of a particle-flow algorithm as described below. The elements are highly inter-related, and must be optimized simultaneously. All figures in this section were generated using GEANT4-based full-detector and test-beam simulation programs and reconstruction algorithms developed by our group.