Performance of a prototype CMS hadron barrel calorimeter in a test beam

We report on the performance of a prototype CMS Hadron Barrel Calorimeter (HCAL) module in a test beam. The prototype sampling calorimeter used copper absorber plates and scintillator tiles with wavelength shifting fibers for readout. Placing a lead tungstate crystal electromagnetic calorimeter in front of HCAL affects the linearity and energy resolution of the combined system to hadrons. The data are used to optimize the choice of total absorber depth, sampling frequency, and longitudinal readout segmentation.