Aging effect in the BESIII drift chamber

TL;DR

This paper investigates the aging effects in the BESIII drift chamber after six years of operation, analyzing gain decreases, aging mechanisms, and mitigation strategies to inform future operation and upgrades.

Contribution

It provides a detailed analysis of aging effects in the BESIII drift chamber and compares calculation methods for gain change, offering practical insights for detector maintenance and upgrade.

Findings

Gain decrease up to 29% in first layer cells

Calculation methods for gain change agree closely

Water vapor addition mitigated Malter effect

Abstract

As the main tracking detector of BESIII, the drift chamber works for accurate measurements of the tracking and the momentum of the charged particles decayed from the reaction of BEPCII e+ and e-. After operation six years, the drift chamber is suffering from aging problems due to huge beam related background. The gains of the cells in the first ten layers experience an obvious decrease, reaching a maximum of about 29% for the first layer cells. Two calculation methods for the gains change (Bhabha events and accumulated charges with 0.3% aging ratio for inner chamber cells) get almost the same results. For the Malter effect encountered by the inner drift chamber in Jan., 2012, about 0.2% water vapor was added to MDC gas mixture to solve this cathode aging problem. These results provide an important reference for MDC operation high voltage setting and the upgrade of the inner drift chamber.