A 10-3 drift velocity monitoring chamber

TL;DR

This paper presents a small, fast-responding drift chamber designed to monitor electron drift velocity in the MEG-II experiment's gas system, ensuring stable detector performance and early detection of gas contamination.

Contribution

Introduction of a simple, highly uniform drift chamber for real-time monitoring of electron drift velocity in particle detectors.

Findings

Achieves prompt detection of drift velocity variations within a minute.

Provides precise measurement of gas quality and contamination sources.

Ensures stable detector operation through continuous gas monitoring.

Abstract

The MEG-II experiment searches for the lepton flavor violating decay: mu in electron and gamma. The reconstruction of the positron trajectory uses a cylindrical drift chamber operated with a mixture of He and iC4H10 gas. It is important to provide a stable performance of the detector in terms of its electron transport parameters, avalanche multiplication, composition and purity of the gas mixture. In order to have a continuous monitoring of the quality of gas, we plan to install a small drift chamber, with a simple geometry that allows to measure very precisely the electron drift velocity in a prompt way. This monitoring chamber will be supplied with gas coming from the inlet and the outlet of the detector to determine if gas contaminations originate inside the main chamber or in the gas supply system. The chamber is a small box with cathode walls, that define a highly uniform electric field inside two adjacent drift cells. Along the axis separating the two drift cells, four staggered sense wires alternated with five guard wires collect the drifting electrons. The trigger is provided by two 90Sr weak calibration radioactive sources placed on top of a two thin scintillator tiles telescope. The whole system is designed to give a prompt response (within a minute) about drift velocity variations at the 0.001 level.