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.

中文翻译：

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用于 HL-LHC ATLAS 强子热量计升级的新型光电倍增管的长期老化研究

大型强子对撞机 (LHC) ATLAS 实验的中央强子热量计 (TileCal) 是一个由约 10,000 个光电倍增管 (PMT) 读出的采样热量计。早期的性能研究表明，PMT 响应随集成阳极电荷的变化而下降。在高亮度大型强子对撞机 (HL-LHC) 计划结束时，读出最多暴露细胞的 PMT 的预期集成阳极电荷为 600 C，其预计响应损失为 25%。这些 PMT（约占 TileCal PMT 总数的 8%）将替换为具有相同几何形状的更新版本 PMT。 Pisa 实验室正在使用测试装置来研究这种新 PMT 模型的长期响应，并将其与 TileCal 目前安装的旧 PMT 模型进行比较。这种新型 PMT 首次在集成超过 800 C 的阳极电荷后进行了测试。本文显示了根据比萨两年多期间收集的数据获得的初步结果。我们还介绍了一项初步研究，旨在理清由于量子效率损失和绝对增益变化对 PMT 响应退化的影响。