Abstract
The channels of TileCal, the hadron calorimeter of the ATLAS experiment at the LHC, are read out with 8-stage fine-mesh photomultipliers (PMTs), a special version of the Hamamatsu model R5900. About 10,000 PMTs are operating in TileCal. The PMT response stability allows to calibrate accurately the calorimeter and to achieve high performance of the energy reconstruction of the cells. Currently, no PMT replacement is foreseen before completion of the High Luminosity program of the LHC collider in the next decade. In this perspective, a number of measurements and tests are in progress to qualify the PMT robustness in terms of lifetime and response stability. Data from the Tile calibration procedure for the detector PMTs and from laboratory tests of spare PMTs are being analyzed. Results on PMT failures, gain loss and quantum efficiency loss are presented. Analysis is focused on the study of the observed down-drift with time of the PMT response as a function of the integrated anode charge, and depending on the individual cell exposure to irradiation during the LHC operation. The multi-stage calibration system of Tile and the algorithms adopted to disentangle between gain and quantum efficiency loss are described, as well as the tests performed in dedicated test-benches.
Highlights
The Tile Calorimeter (TileCal) is a hadronic calorimeter in the central region of the ATLAS detector in CERN’s Large Hadron Collider (LHC).Preprint submitted to Journal NamePlastic scintillator tiles sample the energy deposited in the detector
The TileCal calibration system [1] has been used to monitor the performance of its readout electronics since Run 1, which spanned from 2009-12, as well as during the ongoing Run 2, which started in 2015 [2]
This article presents PMT response studies conducted using the Laser calibration system to determine response down-drift and anticipate future PMT performance in the ATLAS detector
Summary
The Tile Calorimeter (TileCal) is a hadronic calorimeter in the central region of the ATLAS detector in CERN’s Large Hadron Collider (LHC). TileCal is divided into four partitions of 64 modules in azimuth, with each module in the long barrel containing 45 PMTs and each module in the two extended barrels containing 32. This totals to about 10,000 8-stage fine-mesh PMTs, a special version of the Hamamatsu model R5900, that read the light output of all scintillator tiles. The TileCal calibration system [1] has been used to monitor the performance of its readout electronics since Run 1, which spanned from 2009-12, as well as during the ongoing Run 2, which started in 2015 [2] This has involved monitoring the response stability of the 10,000 PMTs, a key function that is necessary for an accurate calibration of signals and reconstruction of events. It discusses a test bench setup in the Pisa-INFN labs that studied the relationship between PMT response down-drift and absolute gain loss, which determined a new statistical method to more accurately calculate PMT absolute gain
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