Role of the CMS electromagnetic calorimeter in the hunt for the Higgs boson in the two-gamma channel

The distinctive signature of the two-photon decay of a low-mass Higgs boson ($H\to\gamma\gamma$) would be a narrow resonance, smeared by the photon energy and direction resolution, over a continuum background of di-photons or spurious events. The sensitivity to this decay mode greatly benefits from the energy and position resolution and photon identification capabilities of the electromagnetic calorimeters at the LHC. In this context, the performance of the electromagnetic calorimeter (ECAL) of CMS - a hermetic, fine grained and homogeneous calorimeter made of lead-tungstate (PbWO$_4$ ) crystals, completed by a silicon lead preshower installed in front of the endcaps - is presented