# VCI2019 - The 15th Vienna Conference on Instrumentation

18-22 February 2019
Vienna University of Technology
Europe/Vienna timezone

## The ultra light Drift Chamber of the MEGII experiment

20 Feb 2019, 11:30
20m
EI9 ()

### EI9

Talk Gaseous Detectors

### Speaker

Dr Malte Hildebrandt (Paul Scherrer Institut)

### Description

The MEG experiment, at the PSI, aims at searching the charged lepton flavor violating decay $\mu^{+}\rightarrow e^{+}\gamma$. MEG has already determined the world best upper limit on the branching ratio: BR<4.2$\times10^{-13}$@90\%CL.
The new positron tracker is a high transparency single volume, full stereo cylindrical Drift Chamber (DC), immersed in a non uniform longitudinal B-field, with length of $1.93~m$ , internal radius of $17~cm$ and external radius of $30~cm$. It is composed of 9 concentric layers, divided in 12 identical sector of 16 drift cells. The single drift cell is approximately square, with a $20~\mu$m gold plated W sense wire surrounded by $40~\mu$m silver plated Al field wires in a ratio of 5:1. The total number of wires amounts to 12288 for an equivalent radiation length per track turn of about 1.45x10$^{-3}$ X$_{0}$ when the chamber is filled with a gas mixture of helium and iso-butane. Due to the high wire density ($12 wires/cm^{2}$), the use of the classical feed-through technique as wire anchoring system could hardly be implemented and therefore it was necessary to develop new wiring strategies. The number of wires and the stringent requirements impose the use of an automatic system (wiring robot) to operate the wiring procedures. Several tests have been performed in different prototypes of the drift chamber, exposed to cosmic rays, test beams and radioactive sources, to fulfill the requirement on the spatial resolution to be less than $110~\mu$m.

### Primary author

Dr Malte Hildebrandt (Paul Scherrer Institut)