Offline filter of data with abnormal high voltage at BESIII drift chamber

Stable operation of the detector is essential for high quality data taking in high energy physics experiments. But it is not easy to keep the detector always running stably, especially during data taking period in an environment with high beam-induced background. In the BESIII experiment, serious beam-related background can cause instability of the high voltages in the drift chamber, the innermost sub-detector. This could result in the decrease of gain and wrong d E /d x measurements. The relationship between the d E /d x measurement and the change in high voltage has been studied. To guarantee the data quality for physics study, an offline event filter algorithm has been developed to remove the data with abnormal high voltages of the drift chamber. After applying the event filter on the data set with serious high voltage problem, the events with wrong d E /d x measurement are removed effectively.