Hadron energy measurement with a highly non compensating quartz fiber calorimeter

The HF calorimeter is a hadronic calorimeter composed of iron absorber with quartz fibers as active medium. The Cerenkov light generated by the relativistic components of the shower is detected by an array of photomultipliers. The construction of the calorimeter, which will cover the pseudorapidity interval 2.8-5.2 (0.6-7 degrees) in the CMS experiment at LHC is being completed at CERN. The main physics goal of the HF calorimeter is to tag high energy jets generated by boson-boson fusion events at LHC. In this paper the results from a test beam exposure at the CERN north area test beam will be presented. Details about the energy response and the response uniformity to electrons and hadrons will be presented. The main part of the talk will be devoted to the studies done to optimize the energy reconstruction algorithm for pions in the energy range 20 to 300 GeV. Special care has to be devoted to this task given that, with its e/h=5, this calorimeter is probably one of the most non compensating hadron calorimeters ever built.