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Abstract
This paper describes the in situ absolute calibration of the Preshower (ES) detector of CMS. Energy deposited in the lead of the Preshower is measured by silicon sensors, allowing a re-scaling of the energy measured by the endcap crystals. Measurement of the energy deposited in the lead absorbers to 5% accuracy is required over a very large dynamic range (1–400 MIPs equivalent); a maximum accuracy of 1% on the measurement of the charge deposited in the silicon will be sufficient. Radiation damage to the sensors (decrease in charge collection efficiency by up to 17% over 10 years) and the electronics (decrease in gain by up to 2% over 10 years) will need to be assessed by periodic in situ calibrations. A precise in situ absolute calibration using particle signals from physics events is examined. It is shown that sufficient calibration accuracy can be obtained by using muon or pion events, and that the time required for the calibration is of the order of a few days at initial LHC luminosity and at least a factor of two less for nominal LHC luminosity.
Highlights
The aim of this work is to simulate full physics events, in the presence of pileup, select MIPs in the Preshower region and attempt to see the single MIP signals
It is assumed that electronics and geometrical effects are already taken into account prior to data taking operation
A short description of the Preshower detector is presented followed by the front-end electronics and the Internal Calibration Circuit
Summary
The aim of this work is to simulate full physics events, in the presence of pileup, select MIPs (minimum ionizing particles) in the Preshower region and attempt to see the single MIP signals. The time necessary for the absolute calibration can be estimated especially for low luminosity running (the most demanding case). It is assumed that electronics and geometrical effects are already taken into account (calibrated) prior to data taking operation. This note concentrates most on effects on sensors (decrease in charge collection efficiency) and electronics (decrease of gain) from radiation damage - i.e. in-situ calibration. A short description of the Preshower detector is presented followed by the front-end electronics and the Internal Calibration Circuit. The calibration procedure is explained with the analysis method to select MIPs and their deposited energies in the Silicon Sensors. The selection criteria and the results are presented. The performance of the calibration procedure is evaluated and the time needed for full Preshower calibration at a module basis is estimated
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