Background Measurements in the CMS Drift Tubes during LHC Run2 and Long Term Irradiation Studies

During the LHC Run2 the background in the CMS Drift Tubes (DT) muon detector was monitored by means of both online anode current measurements and offline analysis. For the offline analysis a method was developed to classify background and signal objects, where objects are either single hits or track segments. The rates as a function of the LHC instantaneous luminosity and the observed spatial distribution of background is presented. Characterizing background as a function of the LHC instantaneous luminosity and observing its spatial distribution helps to understand its sources and to devise mitigation actions to prevent detector early ageing, especially in view of the High Luminosity LHC (HL-LHC) phase. The CMS DT muon detector, built for standing the LHC expected instantaneous and integrated luminosities, will also be used in the HL-LHC at a 3 times larger instantaneous luminosity and, consequently, much higher levels of radiation; reaching about 10 times the LHC integrated luminosity. Long term irradiation measurements of a spare DT chamber were performed at the CERN Gamma Irradiation facility, and the effects of radiation on the DT performance expected during the HL-LHC run are also presented.