Measurement of The Muon Stopping Power in Lead Tungstate

During October-November 2008 the CMS Collaboration conducted a data-taking exercise in order to complete the commissioning of the experiment for extended operation. A large sample of cosmic ray triggered events has been recorded with the solenoid at its nominal axial field strength of 3.8~T. The events collected have been exploited to perform a measurement of specific energy loss of muons in lead tungstate - the electromagnetic calorimeter material - over a wide momentum range (from 5~GeV/c to 1~TeV/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}pm8~GeV, in agreement with expectations.