Characterisation of photomultiplier tubes for the PLUME detector of the LHCb experiment

The Probe for LUminosity MEasurement detector is a luminometer capable of measuring the luminosity and beam conditions of the Large Hadron Collider, at the interaction point of the LHCb. The core of the luminometer is a hodoscope composed of 48 HAMAMATSU R760 photomultiplier tubes. In the first part of this document, the characterization of 29 PMTs of the PLUME detector is presented. It was performed together with the LHCb group of the INFN section of Bologna. For each PMT the gain, the transit time drift, the linearity and the dark current are measured and studied. All the PMTs didn’t report any issue. The mean of the gain values at 1250 V is measured to be (1.493 ± 0.003) × 107. The variation of the transit time depending on the supply voltage is quantified by looking at the transit time drift, which does not exceed the 6 ns between 650 V and 1250 V, the maximum possible voltage range. The PMTs show a non-linearity behaviour of about 30 − 40% in the working regime of 1.5 × 105 gain. The dark current is lower than 10 nA at the maximum allowed voltage value (1250 V). Thanks to this information, the monitoring system of PLUME will be able to correct variations in PMTs performances, during the data taking. The second part of the work was done at the ”Laboratoire de Physique des 2 Infinis Ir`ene Joliot-Curie” (IJCLab) of Orsay. The PLUME modules were tested in a dark box of the laboratory with and without the passage of the light through the optic fiber of the monitoring system, and in the PLUME structure, after the installation.