Study of the EM Barrel Module 0 with muons

Muons contaminating the high energy electron beam have been used to study the EM barrel module~0 response to ''minimum ionising'' particles. The ratio between the muon signal and the noise reaches 7.11$\pm$0.07 when only the middle sampling information are used and reconstructed with an optimal filtering method. The latter increases this ratio by a factor 1.8 with respect to a raw conversion between ADC counts and GeV. From an absolute energy measurement, a $\left( \frac{\mathrm{e}}{\mathrm{\mu}} \right)$ ratio of $0.75\pm0.02$ is derived. As muons deposit their energy in a smaller cluster than the electrons, they can provide cleaner or complementary information on the calorimeter. For example, the modulation of a cell response with~$\Phi$ is larger than with electrons, the modulation in the latter case being smoothed out by the transverse size of the electromagnetic showers. Unlike electrons, muons provide also a mean to test the crosstalk measurements done with calibration runs. A good agreement is found. At last, muons have been used to test the results obtained with electron data on the uniformity of the module response along the $\eta$ direction. With a raw conversion between ADC counts and GeV, a non-uniformity of 4\% (peak to peak) with a 8-fold periodicity is seen, which is compatible with previous analyses. The module response becomes uniform within 0.4\% if optimal filtering coefficients taking into account an absolute electronic calibration of the detector are used. This tends to confirm that the origin of the non-uniformities is probably a missing ground spring in the readout connector of the electrodes.