The new drift chamber of the MEG II experiment

Abstract This article presents the MEG II Cylindrical Drift CHamber (CDCH), a key detector for the phase 2 of MEG, which aims at reaching a sensitivity level of the order of 6 × 1 0 − 14 for the charged Lepton Flavour Violating μ + → e + γ decay (Calibbi and Signorelli, 2018; Cei and Nicolo, 2014). CDCH is designed to overcome the limitations of the MEG e + tracker (Baldini et al., 2013) and guarantee the proper operation at high rates with long-term detector stability. CDCH is a low-mass unique volume detector with high granularity: 9 layers of 192 drift cells, few mm wide, defined by ≈ 12000 wires in a stereo configuration for longitudinal hit localization. The total radiation length is 1 . 5 × 1 0 − 3 X 0 , thus minimizing the Multiple Coulomb Scattering (MCS) contribution and allowing for a single-hit resolution of 110 μ m (Baldini et al., 2016) and a momentum resolution of 130 keV/c. CDCH integration into the MEG II experimental apparatus (Baldini et al., 2018) will start in this year.