The test results on gain stability of hybrid photo-diodes of the CMS hadronic endcap calorimeter

According to necessities of the CMS detector high-rate hybdrid photodiodes (HPD) were used on the hadronic endcap calorimeters (HE). Multialkali photodiode based HPDs respond to these requirements as well as providing a high sensitivity to light emitted by scintillators in calorimeter towers. This structure covers a pseudorapidity range of on the defined projective geometry of the calorimeter. There should be a good synchronization in the values of gain, signalling time, ?etc of all sectors of a well-defined calorimeter for harmonious functioning. This study presents some test results related to the gain stability of HPDs used on the HE.