Calorimetry and photo-detectors
Responsible of the WP: Mathieu Bongrand
Photo-detectors are used in almost every large detector in high energy physics experiments: from dark matter and neutrino experiments to LHC detectors, as well as in astroparticle and nuclear physics. In addition, they also play a major role in the medical diagnostic instrumentation field.
The most common application for photodetectors is the readout of light from scintillators (organic, inorganic and cryogenic) or Cherenkov radiators.
Photomultiplier tubes (PMTs) have been largely used in the last 60 years and characteristics, such as the quantum efficiency and after-pulse, have been greatly improved by a continued R&D effort conducted by industrial companies together with research laboratories. In this field, French teams had a world leading role due to the long-lasting collaboration with the Photonis company. Nowadays, PMTs are still the best choice when large detection areas are required but other photodetectors are gaining popularity. Among them, micro-channel plates PMTs are essential when a precise timing measurement is needed, as for particle identification or Time-of-Flight Positron Emission Tomography (TOF-PET); Silicon Photo-Multipliers (SiPMs) have been rapidly adopted in physics experiments thanks to their insensitivity to the magnetic field, the low operating voltage and the possibility to detect low light signals.
The requests of physics experiments to reach higher levels of precision in light detection and high efficiency over a large dynamic range, going from one to thousands of photons, are strong R&D drivers in the domain of photo-detection. Indeed, future crystal calorimeters will need ultra-fast and radiation-resistant scintillation materials, as well as compact photodetectors with high dynamic range and sensitivity. Precise timing measurement is also a crucial feature for the next generation detectors, not only for particle identification and veto and pile-up rejection for future high-luminosity (HL) LHC experiments, but also for a major improvement in PET imaging. Furthermore, large detectors for neutrino physics experiments require large areas and inexpensive photo-sensors with improved sensitivity to Vacuum Ultra-Violet (VUV) light also will be necessary.
