Measurement of the muon stopping power in lead tungstate with the Electromagnetic Calorimeter in CMS

A large sample of cosmic ray events collected by the CMS detector has been exploited to measure the muon stopping power in the lead tungstate (PbWO$_4$) of the electromagnetic calorimeter. The events were recorded in October-November 2008, during commissioning runs of the CMS detector with the solenoid at the nominal field strength of 3.8~T. The measurement spans a momentum range from 5 to 1000 GeV/c. The results are consistent with the expectations over the entire range. A comparison of collision losses with radiative losses allowed for a first experimental determination of muon critical energy in lead tungstate, measured to be $160^{+5}_{-6}\,({\rm stat.}) \pm8\,({\rm syst.})$~GeV, in agreement with expectations.