Performance and Calibration of CASTOR Calorimeter at CMS

CASTOR (Centauro And Strange Object Research) is a Cerenkov quartz-tungsten sampling calorimeter installed in the very forward region of the CMS experiment covering the pseudorapidity range of $\rm{-5.2}$ to $\rm{-6.6}$. The location of CASTOR and current geometry of the shielding imply operation under relatively high radiation dose and magnetic field. Except for very particular regions, the calorimeter read-out with fine mesh PMTs demonstrates good performance under these rough conditions. Relative calibration of CASTOR is done using beam halo muons. To obtain relevant data, a dedicated CASTOR trigger was developed and activated during beam injections and ramp-ups. The triggered events correspond to an isolated particle penetrating the calorimeter parallel to the beam axis. Analysis of the obtained spectra provides relative response to a muon per individual read-out channel. An absolute CASTOR calibration is not discussed here.