Abstract
In the Compact Muon Solenoid (CMS) experiment at the CERN Large Hadron Collider (LHC), the high resolution Electromagnetic Calorimeter (ECAL), consisting of 75 848 lead tungstate crystals and a silicon/lead preshower, will play a crucial role in the physics program. In preparation for the data taking a detailed procedure was followed to commission the ECAL readout and trigger, and to pre-calibrate, with test beam and cosmic ray data, each channel of the calorimeter to a precision of 2% or less in the central region. The first LHC collisions have been used to complete the detector commissioning and will have to provide the first in situ calibration. In this talk the CMS ECAL status and performance with the first collisions delivered from LHC will be reviewed.
Highlights
The Compact Muon Solenoid (CMS) detector [1] [2] is one of the two general purpose detectors installed at the CERN Large Hadron Collider (LHC)
The Higgs width is very narrow and the signal lies above an irreducible background: this led to the choice of a high resolution electromagnetic calorimeter
The electromagnetic calorimeter (ECAL) [1] [3] of the CMS, located within a 3.8 T superconducting solenoid, is a hermetic homogeneous calorimeter comprised of lead tungstate (PbWO4) crystals and a lead-silicon preshower
Summary
The Compact Muon Solenoid (CMS) detector [1] [2] is one of the two general purpose detectors installed at the CERN LHC. To gain rejection power against fake photons from neutral pion decays, a preshower detector is located in front of the crystals in the pseudo rapidity range |1.65| < η < |2.6|: two lead radiators (two and one radiation length thick) initiate electromagnetic showers from the incoming photons and electrons, and silicon strip sensors placed after each radiator measure the energy deposited and the transverse shower profiles. The target value for the energy resolution of the calorimeter at high energies is less than 0.5% With these performances a Higgs boson with a mass of 120 GeV could be observed by the CMS in the gamma gamma decay with a 5-σ significance collecting less than 10 fb−1 [5]
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