Long term aging studies of the new PMTs used for the HL-LHC ATLAS hadron calorimeter upgrade

• Published in: Journal of instrumentation 2024-03, Vol.19 (3), p.C03051
• Main Authors: Chiarelli, G., Leone, S., Scuri, F.
• Format: Article
• Language: English
• Subjects: Large Hadron Collider; Luminosity; Performance degradation; Photomultiplier tubes; Quantum efficiency
• ISSN: 1748-0221; 1748-0221
• DOI: 10.1088/1748-0221/19/03/C03051

The central hadron calorimeter (TileCal) of the ATLAS experiment at the Large Hadron Collider (LHC) is a sampling calorimeter read out by about 10,000 photomultipliers (PMTs). Earlier studies of performance showed a degradation in PMTs response as a function of the integrated anode charge. At the end of the High-Luminosity LHC (HL-LHC) program, the expected integrated anode charge for PMTs reading out the most exposed cells is 600 C, and their projected response loss is 25%. These PMTs (≈ 8% of the total TileCal PMTs) will be replaced with a newer version PMT with the same geometry. A test set-up is being used in the Pisa laboratory to study the long term response of this new PMT model and compare it to the old PMT model currently installed in TileCal. For the first time this new PMT has been tested after integrating more than 800 C of anode charge. Preliminary results obtained from data collected in Pisa over a period exceeding two years are shown in this paper. We also introduce a preliminary study aimed to disentangle the contribution to the PMT response degradation due to the loss of quantum efficiency and to the change in absolute gain.