Abstract
In the mass range of 110–150 GeV the favored process for Higgs boson detection via p-p collisions is via its decay into two photons, which demands a very high-resolution electromagnetic calorimeter. This physics goal plus the Large Hadron Calorimeter (LHC)-imposed design constraints of 25ns bunch spacing and a hostile radiation environment have led the Compact Muon Solenoid (CMS) collaboration to the choice of lead tungstate (PbWO 4) crystals. These factors plus the presence of a 4T magnetic field and the relatively low room-temperature scintillation photon yield of PbWO 4 make photodetection a real challenge, which CMS has met via the choice of devices providing gain amplification: Avalanche photodiodes (APD) in the central barrel region and vacuum phototriodes (VPT) in the forward and backward endcap regions. In the past year the CMS electromagnetic calorimeter has entered the construction phase. We review progress in the areas of crystals, barrel and endcap photodetection devices, plans for detector calibration as well as the status of assembly and quality control. We also invoke relevant developments in other crystal calorimeters currently in operation or under development. Crystal calorimeters remain the medium of choice for precision energy and position measurements in high energy physics.
Highlights
Crystal calorimeters have historically been used in high energy physics for precision energy measurements of electromagnetically-interacting particles such as e, γ and π0, and to help in precision position measurements
To achieve a targeted mass resolution of σ(M)/M
The photoelectric currents from the Avalanche photodiodes (APD)/vacuum phototriodes (VPT) will be processed by a ’light-to-light’ on-detector readout chain consisting of only radiation-hard components[11, 18, 19]
Summary
Crystal calorimeters have historically been used in high energy physics for precision energy measurements of electromagnetically-interacting particles such as e, γ and π0, and to help in precision position measurements. The PbW04 crystals have been chosen in order to optimize the probability of observing the Higgs boson in the mass range of 110-150 GeV via its decay into 2 photons, which demands a very high-resolution ECAL and in particular maximal longitudinal containment of electromagnetic showers. To achieve a targeted mass resolution of σ(M)/M
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