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 ± 8 GeV, in agreement with expectations.