The CMS Muon Drift Tubes HL-LHC Upgrade Demonstrator at Run 3 Start

The electronic system of the CMS Drift Tubes (DT) chambers will be replaced to operate during High Luminosity (HL-LHC). The upgraded architecture ships all signals to the backend, where complex logic will be performed with a precision matching the maximum chamber resolution, now only available offline. A demonstrator has been installed during Long Shutdown 2 (LS2) in one of the sixty sectors of the detector. Over LS2 we have integrated this system in CMS operations environment and tested its stability over extended cosmics data-taking campaigns, also with the magnetic field on. This paper describes the time synchronization achieved and early performance in collisions at Run3 start.