RICH detectors, detectors for medical imaging, photosensors
and read-out electronics

We collaborate in large international collaborations, where particle identification is crucial part of the analysis of decays. Our work is focused on the design and development of Ring Imaging Cherenkov Counters. We were involved in the design and operation of HERA-B RICH, and two Belle II particle identification detectors: Aerogel RICH and Time-Of-Propagation Counter. HERA-B RICH used a C4F0 gas radiator and a large 24 m² spherical mirror for imaging Cherenkov rings. Single photons were detected by 2240 Hamamatsu multi-anode photomultipliers with about 27,000 channels. It was the first Ring Imaging Cherenkov Counter that used multi-anode photomultipliers for photon detection. The strong contribution of teh Ljubljana team and coordination of the research activities by Peter Križan resulted in fully reached design goals.

We study photon sensors for the new generation of Cherenkov ring detectors (RICH). Due to HL-LHC upgrade, the particle fluxes will increase so that multi-anode photomultipliers currently used for detecting photons in LHCb RICH, will have to be replaced by a photon sensor with increased granularity. Hybrid Avalanche Photon detectors of Belle II RICH with an Aerogel radiator will also not be able to operate after the Belle II long term upgrade. In our laboratory we are exploring new detection concepts and possibilities for both upgrades. We are developing a silicon photomultiplier, single-photon sensor that will be very fast, will have fine granulation, will be sensitive to light of long wavelengths and withstand radiation load, mainly due to neutron flux. As an alternative, we study Large Area Picosecond Photon Detector, based on microchannel PMT technology. We design and construct the prototypes of RICH detectors, test them in our laboratory and evaluate them In the high-energy charged particle test beams at CERN, Geneva, DESY, Hamburg and KEK, Japan.

Experimental particle physics strives to develop and master state-of-the-art technology. Innovations from our laboratories can be usefully transferred to other areas. Nuclear medicine is a successful example where we are introducing advances in photodetectors and reading electronics to improve detector technology.

Leveraging our experience from the design and deployment of Cherenkov detectors in experimental particle physics, we have developed a novel positron emission tomography (PET) detector based on prompt Cherenkov photons. Cherenkov PET detectors can be built from low-cost lead fluoride (PbF₂) crystals, and enable excellent time-of-flight (TOF) resolution. In 2011, we experimentally demonstrated a TOF resolution of 95 ps FWHM. We have shown that by using advanced detector geometries, the fundamental limit to Cherenkov TOF PET resolution due to physical process in the crystal is only 22 ps FWHM. We produced two multi-channel Cherenkov TOF PET modules, integrated with fast readout electronics, and experimentally demonstrated Cherenkov PET image reconstruction for the first time. Our latest simulation studies show that whole-body Cherenkov TOF PET scanners produce image quality at least equal to state-of-the-are clinical scanners [G. Razdevšek et al., see Publications].

Advanced photon detectors play an important role in different areas. We focus on single-photon detection for charged particle identification in HEP experiments to fast photon detection for medical applications and applications in life sciences. We are studying the properties of the different vacuum, solid-state and vacuum detectors. In different experimental setups, we measure the position dependence of the time and charge response of the detectors to short laser light pulses.
We have been working with multi-anode photomultipliers since 1996. We have successfully deployed 16 and 4 channel versions in the HERA-B RICH, used them in a variety of environmental applications and continued their exploration with 64 channel devices in the LHCb RICH.

In recent years much effort has been spent developing readout electronics and photodetectos for the needs of future high luminosity high energy physics experiments. Big improvements in performance and cost-efficiency of such technologies were achieved, which can also benefit other applications. We have developed a novel fluorescence lifetime measurement system based on the latest silicon photomultiplier photodetectors and signal digitization approaches. Fluorescence lifetime measurements are used in a wide range of applications in life sciences, for example, imaging of cell structures in biology, detection of cancer cells in medicine and protein binding assays in pharmacy. However, due to intrinsic limitations of the typically used time-correlated single-photon counting (TCSPC) method, the fluorescence lifetime measurements require sophisticated instrumentation and a certain time for acquisition.