Study of PMT Response Jumps at Start of Collisions

The Laser calibration became the main calibration system of ATLAS hadronic barrel calorimeter (Tilecal) as the usage of the system using Cs source in the calorimeter is restricted to periods when access to the calorimeter is possible. During physics runs it was noted the response of the PMT to laser pulses changes before and after the start of collisions. Here we report the study of the stability of the laser response within physics laser runs and implement improvements in the current analysis code.