The NA62 hadron calorimeter

NA62 is a fixed target experiment located in the north area of CERN. The ambitious aim of the experiment is the measurement of the branching ratio ($Br$) of the very rare decay $K^{+} \to \pi^{+} \nu \bar{\nu}$ within 10% precision using a decay-in-flight technique. The branching ratio of this decay is very well calculated in the standard model as $(9.11 \pm 0.72) \times 10^{11}$ and the measurement of this channel represents one of the most promising fields for the search of new physics beyond the standard model. The presence of just one detectable track in the final state is an enormous challenge for any experiment. The decay is fully reconstructed, which leads to a strong background suppression. Still the detector resolution, combined with the tiny branching ratio of the signal, makes the $K^{+} \to \mu^{+}\nu$ decay (whose $Br$ is 0.64) a critical source of background. The NA62 detector was therefore designed to perform an excellent $\pi / \mu$ separation using a very efficient particle identification system. A major role is played by the calorimeters that provides a muon rejection factor of the order of $10^{5}$ through the measurement of energy and shape of the hadronic showers. The calorimetric system consists of an electromagnetic calorimeter filled with liquid krypton and a hadron calorimeter. This presentation, after illustrating the HAC structure, reports on the calibration procedure of the detector response and preliminary results of the performance of the hadronic energy reconstruction.