A Study of Hadronic Calibration Schemes for Pion Test Beam Data in the ATLAS Forward Calorimeter

The ATLAS forward calorimeters constitute a small though important fraction of the detector's calorimeter system, designed in part to accurately and precisely measure the energy of particles and jets of particles originating from the collisions of high-energy protons at the detector's centre. The application of hadronic weights, a practice common in high-energy calorimetry, provides a means of compensation for the fraction of energy which is deposited by particles in the detector, but which is invisible to the detector due to the nature of hadronic showers. Explored here are various schemes of extracting hadronic weights, as well as the application of such weights, based on pion data from the 2003 ATLAS forward calorimeter test beam. During the collection of test beam data, beams of both pions and electrons of known energy, ranging from 10 to 200 GeV, were fired at specific points of an isolated detector in order to understand its response. The improvement in noise-subtracted energy resolution with respect to the electromagnetic scale results, based on a weighting scheme which takes advantage of the transverse properties of hadronic showers, is shown to be 34.5% at an energy of 200 GeV. In terms of the energy response, it is shown that upon application of hadronic weights for such a weighting scheme, one is able to reconstruct the pion energy to within 5% of its true value for all test beam energies above 40 GeV. It is also shown that hadronic weights can be applied without taking advantage of the tracking information used in the test beam setup, in an effort to show the feasibility of such methods in the analysis of ATLAS collision data. Furthermore, the difficulties present in accurately reconstructing the energy in the high-77 region of the detector due to the presence of the ATLAS beam pipe and the means of compensating for such difficulties are investigated.