Electromagnetic response of a highly granular hadronic calorimeter

The CALICEcollaboration is studying the design of high performance electromagnetic and hadronic calorimetersfor future International Linear Colliderdetectors. For the hadronic calorimeter, one option is a highly granular sampling calorimeterwith steel as absorber and scintillatorlayers as active material. High granularity is obtained by segmenting the scintillatorinto small tiles individually read out via silicon photo-multipliers (SiPM). A prototype has been built, consisting of thirty-eight sensitive layers, segmented into about eight thousand channels. In 2007 the prototype was exposed to positrons and hadronsusing the CERN SPS beam, covering a wide range of beam energies and angles of incidence. The challenge of cell equalization and calibration of such a large number of channels is best validated using electromagnetic processes. The response of the prototype steel- scintillator calorimeter, including linearity and uniformity, to electrons is investigated and described.