Secondary scintillation yield from gaseous micropattern electron multipliers in direct Dark Matter detection

摘要

Efforts are being made in direct Dark Matter search experiments to detect the primary ionisation inthe liquid by extracting the electrons to the gas phase and use the secondary ionization produced inthe micropattern electron multipliers for signal amplification in noble-liquid dual-phase TPCs. We havestudied the secondary scintillation yield of a single Gas Electron Multiplier (GEM) and of a Micro-Hole Strip Plate (MHSP) for xenon at room temperature. Values for secondary scintillation yield between5.0×103 and 1.3×103 photons per primary electron were obtained for the GEM and between 7.2×104and 1.8 × 103 photons per primary electron for the MHSP, as the pressure increased from 1.0 to 2.5 barin the GEM-setup and from 1.0 to 3.3 bar in the MHSP-setup, respectively. These values can be more thanone order of magnitude higher than what has been obtained in the uniform-field scintillation gaps of theXENON and ZEPLIN-III experiments. Although in the present setups the amount of secondary scintillationobtained is sufficient in view of the use of PMTs, if a different type of readout is considered, such aslarge area avalanche photodiodes, it will be important to increase the amount of secondary scintillation.The attained results demonstrate the clear advantage of reading the secondary scintillation instead of thecharge produced in the electron avalanches of micropattern electron multipliers, in low-background andlow-rate experiments, as is the case in direct Dark Matter search.