Speaker
Description
Ultra-low mass drift chambers, with Helium-based gas mixture and high wire density are ideal trackers for high-precision experiments in the intensity frontiers of particle physics. In the search for Lepton Flavor Violation the MEG~II experiment at the Paul Scherrer Institut represents the state of the art in the search for the $\mu^+~\rightarrow~e^+~\gamma$ decay. The Cylindrical Drift CHamber (CDCH) is a key detector for MEG~II with single-hit, angular and momentum resolutions $< 120$~$\mu$m, 6.5~mrad and 100~keV/c respectively, measured on data. Wire breaking problems arose during the assembly and commissioning phases due to galvanic corrosion of the 40-50~$\mu$m Silver-plated Aluminum cathode wires in presence of ambient humidity. A R$\&$D work started to find an alternative wire solution and explore the possibility to build a new chamber. The CDCH2 project was approved and is currently in the construction phase at INFN Pisa. Given the high wire density (12~wires/cm$^2$), a modular assembly is used. Wires are not strung directly on the through-hole endplates but fixed at both ends on the pads of two PCBs, which are then radially stacked on the endplates. Al (5056 alloy) 50~$\mu$m cathode wires without Ag coating were chosen, since their immunity to corrosion. A hybrid wire fixing technology was developed since the known difficulties to solder very thin Al wires, due to the natural oxide layer. Automatic laser micro-soldering and micro-gluing stations are integrated in the wiring machine, which ensures a 50~$\mu$m and $\pm 0.5$~g wire placement and mechanical tension accuracy. A special soldering tin with acid flux core allows the Al wire soldering and electric contact. A drop of epoxy glue is then used to mechanically secure the Al wire. This novel technique is now well established, allowing to reach the 70\% of the CDCH2 assembly. The completion goal is set in June 2024.
| Collaboration | MEG |
|---|---|
| Role of Submitter | I am the presenter |
