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

The central hadron calorimeter of the ATLAS experiment at the Large Hadron Collider (LHC) is readout by about 10,000 photomultipliers (PMTs). Earlier studies of performance showed a degradation in PMT’s response as a function of the integrated anode charge. A model of the time evolution of the PMT response was made, with a projected loss exceeding 25% for the fraction of the PMTs (about 8% of the total) that will integrate an anode charge of 600 C, expected at the end of the High-Luminosity LHC program. These PMTs will be replaced with a newer version, in order to keep the global detector performance at an optimal level. A local test setup is being used in the Pisa laboratory to study the long term response of a new PMT model considered for replacement in the hadron calorimeter readout of most active cells. For the first time this new PMT model has been tested after integrating more than 250 C of anode charge. Preliminary results obtained from data collected in the Pisa laboratory are shown in this presentation