Analysis and correction of the magnetic field effects in the Hybrid   Photo-Detectors of the RICH2 Ring Imaging Cherenkov detector of LHCb
  The Ring Imaging Cherenkov detectors of the LHCb experiment at the Large Hadron Collider at CERN are equipped with Hybrid Photo-Detectors. These vacuum photo-detectors are affected by the stray magnetic field of the LHCb magnet, which degrades their imaging properties. This effect increases the error on the Cherenkov angle measurement and would reduce the particle identification capabilities of LHCb. A system has been developed for the RICH2 Ring Imaging Cherenkov detector to perform a detailed characterisation of the magnetic distortion effects. It is described, along with the methods implemented to correct for these effects, restoring the optimal resolution. 
R. Cardinale, C. D'Ambrosio, R. Forty, C. Frei, T. Gys, A. Petrolini,   D. Piedigrossi, B. Storaci and M. Villa
physics.ins-det hep-ex