Mitigation of Anomalous APD signals in the CMS ECAL

Anomalous, large signals are observed in the barrel part of the CMS Electromagnetic Calorimeter during pp collisions. Laboratory and beam-test studies, as well as Monte Carlo simulations, have been used to understand their origin. They are ascribed to direct energy deposition by particles in the Avalanche Photo-Diodes used for the light readout. Their properties and rates are summarized, including predictions for the future. The methods that have been employed to reject these signals in the trigger and the reconstructed data are presented. The importance of these signals as backgrounds to physics analyses in CMS is also discussed.