The Search for $\mu^+\to e^+ \gamma$ with 10$^{-14}$ Sensitivity: the Upgrade of the MEG Experiment

The MEG experiment took data at the Paul Scherrer Institute in the years 2009--2013 and published the most stringent limit on the charged lepton flavor violating decay $\mu^+\to e^+ \gamma$: BR($\mu^+\to e^+ \gamma$) $<4.2 \times 10^{-13}$ at 90% confidence level. The MEG detector has been upgraded in order to reach a sensitivity of $6\times10^{-14}$. The basic idea of MEG II is to achieve the highest possible sensitivity using the available muon beam intensity at the Paul Scherrer Institute ($7\times10^{7}$ muons/s) with an improved detector. The key improvements are increased rate capability of all subsystems and increased resolutions while maintaining the same detector concept. In this paper, we present the current status of the preparation, integration and commissioning of the MEG II detector in the recent engineering runs.