6th International Workshop on New Photon-Detectors (PD24)

19 Nov 2024, 00:20 → 22 Nov 2024, 10:30 US/Pacific

1400-1430 (Harbour Centre, Vancouver (BC), Canada)

Fabrice Retiere, Giacomo Gallina

The 6th International Workshop on new Photon-Detectors (PD24) will be held November 19-21, 2024 at Simon Fraser University, Harbour Centre in Vancouver, BC, Canada.

PD24 is an international workshop organized jointly by TRIUMF, Simon Fraser University (SFU), the Gran Sasso Science Institute (GSSI) and Princeton University.

PD24 will discuss recent progress and developments of photo-sensors including SiPMs, MCPs, APDs, PMTs, hybrid PMTs and digital photon sensors.  Furthermore, the workshop will cover the multifaceted applications of these technologies across diverse fields such as particle and astroparticle physics, nuclear physics, nuclear medicine, astronomy, and associated instrumentation. 

The workshop program will include plenary sessions with invited and contributed talks. There will also be a poster session.

The event will be in-person format with regular and poster sessions. A few virtual presentations will be available on demand. 

Conference proceedings will be published on JINST!

Previous Photon-Detectors workshops: 2018, 2015, 2012, 2009, 2007

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Please review the Important Dates and the Visa information webpages.  We strongly encourage applicants who need a visa to travel to Canada to submit their abstract before the "Early Abstract Submission deadline" due to long visa processing times.

• Abstract Submission opens: 15-June 2024 Now Open!

• Early Abstract Submission deadline: 15-July-2024 

• Late Abstract Submission deadline: 31-Aug-2024 15 Sept 2024 ! (Extended)

• Registration Opens & Hotel Information Published on Indico: 18-Sept 2024 Now Open! Check the Indico Page "Workshop Registration"

• Early Registration Closes: 1 Oct 2024

• Registration Closes: 5 Nov 2024

   

Territorial Land Acknowledgement

TRIUMF is located on the traditional, ancestral, and unceded territory of thexʷməθkʷəy̓əm (Musqueam) people, who for millennia have passed on their culture, history, and traditions from one generation to the next on this site.

Simon Fraser University respectfully acknowledges the xʷməθkʷəy̓əm (Musqueam), Sḵwx̱wú7mesh Úxwumixw (Squamish), səlilwətaɬ (Tsleil-Waututh), q̓íc̓əy̓ (Katzie), kʷikʷəƛ̓əm (Kwikwetlem), Qayqayt, Kwantlen, Semiahmoo and Tsawwassen peoples on whose unceded traditional territories our three campuses reside.

 

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Tuesday 19 November

08:00 Registration

Opening Session

1 Organization

Speaker: Giacomo Gallina

2 Opening

Speaker: Fabrice Retiere

Colliders

3 Single-photon detectors for particle identification in high-energy physics experiments

A review of single-photon detectors used in particle identification systems for high-energy physics experiments is presented. Different detector technologies will be reviewed, including photomultiplier tubes, microchannel plate photomultiplier tubes, Geiger-mode avalanche photodiodes and hybrid photodetectors.

Speaker: Massimiliano Fiorini (Universita e INFN, Ferrara (IT))

4 SiPM radiation damage

The current understanding of radiation tolerance of Silicon Photomultipliers (SiPMs) is reviewed. Methods to characterize irradiated SiPMs after their single photo-electron resolution is lost are discussed and ideas are presented on how to approach the development of radiation hard SiPMs.

Speaker: Dr Yuri Musienko (University of Notre Dame and INR RAS (Moscow))

5 Silicon Photomultipliers in the CMS Upgrade

Silicon Photomultipliers (SiPM) will be used extensively in the upgraded CMS detector at the Large Hadron Collider. SiPMs have already been implemented into the barrel and endcap hadron calorimeters as part of the Phase I upgrade, and hundreds of thousands of SiPMs will be used for two new Phase II subdetectors, the Barrel Timing Layer and the endcap high granularity hadronic calorimeter. We will discuss the motivation for SiPMs as the photodetectors of choice in CMS, the evolution of the SiPMs from Phase I to Phase II, and the particular challenges faced and overcome for each of the three subdetectors.

Speaker: Mitchell Ross Wayne (University of Notre Dame (US))

Coffee Break

Colliders

6 Test beam performance of a novel compact RICH detector with timing capabilities for the future ALICE 3 PID system at LHC

The ALICE Collaboration is proposing a completely new apparatus, ALICE 3, for the LHC Run 5 and beyond. A key subsystem for high-energy charged particle identification will be a Ring-Imaging Cherenkov (RICH) detector consisting of an aerogel radiator and a photodetector surface based on Silicon Photomultiplier (SiPM) arrays in a proximity-focusing configuration. A thin high-refractive index slab of transparent material (window), acting as a second Cherenkov radiator, is glued on the SiPM arrays to achieve precise charged particle timing. Requiring time matching between aerogel Cherenkov photon and track hits also leads to an improvement of pattern recognition by discarding the uncorrelated SiPM dark count hits.

We assembled a small-scale prototype instrumented with different Hamamatsu SiPM array sensors with pitches ranging from 1 to 3 mm. The Cherenkov radiator consisted of a 2 cm thick aerogel tile with a refractive index of 1.03. SiPM arrays coupled with two different window materials (SiO2 and MgF2) were used. The prototype was successfully tested in beam test campaigns at the CERN PS T10 beam line.

The data were collected with a complete chain of front-end and readout electronics based on the Petiroc 2A and Radioroc 2 together with a picoTDC to measure charges and times. We measured a charged particle detection efficiency above 99% and a single photon angular resolution better than 4 mrad with time resolution better than 70 ps on the tracks of charged particles.

In this talk we present the current status of the R&D performed for the ALICE 3 RICH detector and the expected full scale system performance. A special focus will be given to the beam test results obtained with the RICH prototype.

Speaker: Nicola Mazziotta (Universita e INFN, Bari (IT))

7 Development of microlens-enhanced SiPMs

The LHCb experiment at CERN has been upgraded for the Run 3 operation of the Large Hadron Collider (LHC). A new concept of tracking detector based on Scintillating Fibres (SciFi) read out with multichannel silicon photomultipliers (SiPMs) was installed during its upgrade. One of the main challenges that the SciFi tracker will face during its operation is the high radiation environment due to fast neutrons. In view of LHCb Upgrade II in 2033, the radiation levels will increase significantly and the SciFi tracker must undergo a major upgrade. A novel concept of adding microlenses at the wafer level aligned to the SiPM pixelised structures has been developed. The microlens enhance the PDE of the SiPM significantly and reveal advantages for correlated noise and timing performance. A simulation to optimise the microlens implementation parameters has been validated. It allows us to evaluate the microlens performance as a function of incident light angular distribution and geometrical properties of the pixel implementation. An overview of the results obtained, the future possibilities, and an outlook of our activities with FBK and Hamamatsu are given

Speaker: Guido Haefeli (EPFL - Ecole Polytechnique Federale Lausanne (CH))

8 SiPM developments for the Time-Of-Propagation detector of the Belle II experiment

Belle II is a particle physics experiment planning to work in a high luminosity condition that expects a hard irradiation environment in the next few years. The Time-Of-Propagation modules surround the Belle II tracking detector on the barrel part for particle identification. Each module contains a finely fused silica bar, microchannel plate photomultiplier tube (MCP-PMT) photo-detectors, and high-speed redout electronics. These MCP-PMTs will have a lifetime of about one year at the nominal luminosity of the accelerator due to the high photon background degrading the quantum efficiency of the photocathode. An alternative for these MCP-PMTs can be multi-channel photon counters (MCPC) known as silicon photomultipliers (SiPM). The SiPMs in comparison to MCP-PMTs have a lower cost and higher photon detection efficiency, but also a higher dark count rate with an exponential increase as a function of the neutron background rate. The dark count rate can be mitigated with an annealing process and lower temperatures. We tested SiPMs from different producers and different dimensions and cell pitches to understand functionality and behavior in several conditions, e.g. irradiation up to 5x10^11 n/cm^2 or after strong annealing for 60 days at 150 degrees Celsia. Dark count rate studies demonstrate significant recovery of the degradation of SiPMs using annealing. In the photon spectra analyses, we are able to nicely extract photon peaks and estimate breakdown voltages, which are consistent in different conditions. In time resolution examinations, the SiPMs achieve a 100 ps level, and the results are compatible in all tested conditions. A new SiPM prototype developed in collaboration with FBK with the aim of improving radiation hardness, is expected to be delivered at the end of August 2024.

Speaker: Jakub Kandra

Lunch Break

Colliders

9 Cryogenic operation of neutron-irradiated SiPM arrays from FBK and Hamamatsu

The LHCb experiment at CERN has been upgraded for the Run 3 operation of the Large Hadron Collider (LHC). A new concept of tracking detector based on Scintillating Fibres (SciFi) read out with multichannel silicon photomultipliers (SiPMs) was installed during its upgrade. One of the main challenges that the SciFi tracker will face during its operation is the high radiation environment due to fast neutrons, where the SiPMs are located. In view of LHCb Upgrade II in 2033, the radiation levels will increase significantly and the SciFi tracker must undergo a major upgrade. By the end of the lifetime, the expected radiation fluence reaches 3E12 neq/cm2 at the SiPMs location. To cope with the increase in radiation, cryogenic cooling with liquid Nitrogen is being investigated as a possible solution to mitigate the performance degradation of the SiPMs induced by radiation damage. Thus, a detailed performance study of different layouts of SiPM modules produced by FBK and Hamamatsu is being carried out. These detectors have been designed to operate at cryogenic temperatures. Several detectors were irradiated at Ljubljana at different neutron fluences and have been tested in a dedicated cryogenic setup down to 100K. Key performance parameters such as breakdown voltage, dark count rate, photodetection efficiency, cross-talk, and after pulsing are being characterized as a function of the temperature, over-voltage, and neutron fluence. The main results of this study are going to be presented.

Speaker: Esteban Curras Rivera (EPFL - Ecole Polytechnique Federale Lausanne (CH))

10 The SiPM readout plane for the ePIC-dRICH detector at the EIC: overview and beam test results

The dual-radiator (dRICH) detector of the ePIC experiment at the future Electron-Ion Collider (EIC) will make use of SiPM sensors for the detection of the emitted Cherenkov light. The photodetector will cover $\sim$ 3 m$^{2}$ with 3 $\times$ 3 mm$^{2}$ pixels, for a total of more than 300000 readout channels and will be the first application of SiPMs for single-photon detection in a HEP experiment. SiPMs are chosen for their low cost and high efficiency in magnetic fields ($\sim$ 1 T at the dRICH location). However, as they are not radiation hard, careful testing and attention are required to preserve single-photon counting capabilities and maintain the dark count rates (DCR) under control over the years of running of the experiment. DCR control can be achieved with operation at low temperature and recovery of the radiation damage via high-temperature annealing cycles. The exploitation of the SiPMs precise timing with fast TDC electronics helps reducing further the effect of DCR as background signal.

In this talk we present an overview of the ePIC-dRICH detector system and the current status of the R&D performed for the operation of the SiPM optical readout subsystem. Special focus will be given to recent beam test results of a large-area prototype SiPM readout plane consisting of a total of up to 2048 3$\times$3 mm$^{2}$ sensors. The photodetector prototype is modular and based on a novel EIC-driven photodetection unit (PDU) developed by INFN, which integrates 256 SiPM pixel sensors, cooling and TDC electronics in a volume of $\sim$ 5$\times$5$\times$14 cm$^{3}$. Several PDU modules have been built and successfully tested with particle beams at CERN-PS in October 2023 and in May 2024. The data have been collected with a complete chain of front-end and readout electronics based on the ALCOR chip, developed by INFN Torino.

Speaker: Roberto Preghenella (INFN, Bologna (IT))

Astroparticles, Astrophysics and Astronomy

11 Development of a Wide-Band Gamma-Ray Camera Onboard a 50 kg-Class Small Satellite GRAPHIUM

More than 300 satellites are being developed worldwide, some of which are used to promote the space sciences. Waseda University and Tokyo-Tech are developing a 50 kg-class satellite “GRAPHIUM,” scheduled for launch in FY2026. The satellite aims to expand MeV gamma-ray astronomy that has stagnated for over 30 years. The primary detector of the satellite is a box-type Compton camera (INSPIRE) that covers a dynamic range spanning over two orders of magnitude by observing low energy (30–200 keV) in the pinhole mode and high energy (200 keV– 3 MeV) in the Compton mode. The CC-BOX consists of pixelized Ce:GAGG scintillators coupled with an MPPC array covering a total geometric area of 10 × 10 cm², surrounded by BGO active shields. The scatterer has a 5-mm square pinhole that enables imaging using low-energy gamma rays according to the principle of a pinhole camera. The rear absorber has a four-layer depth-of-interaction (DOI) structure with a total thickness of 20 mm that improves sensitivity to MeV gamma rays. Consequently, the location of the gamma-ray interaction is identified three-dimensionally by reading of the signals by the MPPC at both ends of the scintillators. This significantly improves the spatial resolution of the detector . The design of the CC-BOX is now complete, and we have developed an engineering model (EM) equipped with actual sensors.
In this presentation, first, we describe the detailed configuration of INSPIRE, including its data acquisition (DAQ) and power supply system. Then, we evaluate the operating system and data processing flow, including a DAQ board, USB board, and Raspberry Pi. Finally, we present the results of wide-band imaging performed using the EM and discuss its performance in terms of energy and angular resolution.

Speaker: Mr Ryohei Mori (Waseda University)

12 Dichroicons: Spectral Photon Sorting for Neutrino Detectors

Many neutrino detectors use photons as their primary event detection method, typically detecting numbers of photons and their arrival times. Photons also carry information about an event through their wavelength, polarization, and direction, but often little to none of this information is utilized. The "dichroicon," a Winston-style light cone comprised of dichroic filters, allows detectors to use the wavelength information encoded in photons. This talk will discuss measurements of the performance of the dichroicon at the CHESS detector, focusing on the dichroicon's scintillation and Cherenkov photon detection and separation efficiency. The results will include measurements from two types of dichroicons paired with water based and liquid scintillators exposed to radioactive and cosmogenic sources. In addition to the benchtop results, the talk will discuss the deployment of dichroicons in Eos, a 20 ton hybrid Cherenkov-scintillation detector. The Eos detector is a demonstrator for very large scale neutrino detectors, including Theia, and features the first deployment of 12 large-scale monolithic dichroicons. Preliminary measurements of the performance of the dichroicons in the Eos detector will be presented, as well as predictions of the performance in future detectors like Theia. These results will include studies of the collection efficiency and discrimination between Cherenkov and scintillation light, new handles on particle ID, and novel reconstruction techniques that leverage the advantages of both Cherenkov and scintillation light.

Speaker: Joshua R Klein (University of Pennsylvania (US))

13 Performance of Large-Area 1D CRL Position Sensitive Silicon Photomultiplier Array

The applications of previously reported two-dimensional (2D) Cap Resistive Layer (CRL) Position Sensitive (PS) SiPM were limited due to their small 6.14×6.14 mm² active area and position distortions at corner due to interaction between adjacent strip metal electrodes. In this study, we developed a 4×4 array of 1D CRL PS SiPMs with total active area of 24.6×24.6 mm². By employing a cathodes and anodes multiplexing technology based on resistors network, its readout channels are greatly reduced into two anodes and two cathodes. The coarse 1D position coordinate, i.e., which row of the array is impinged by photons, is determined from two cathode signals based on charge division mechanism of external resistors. Meanwhile, the fine 1D position coordinate, i.e., the relative position of incident light relative to the anode readout channels of pixel 1D CRL PS SiPM, is derived from the two anode signals utilizing the charge division mechanism facilitated by the intrinsic cap resistor of the 1D CRL PS SiPM. In this way, large active area of the array, high position and timing resolution can be achieved while retain less readout channel.
The preliminary results will be presented in this talk. Under a mean photoelectron number of approximately 130 and bias voltage of 32 V, the position measurement error was 54.8 ± 38.3 µm, about 0.23% of the edge length of the array, position resolution was 392.9±58.3 µm, and time resolution was 205.3±22.3 ps. Additionally, by perpendicularly arranging two 1D CRL PS SiPM arrays at the end of a scintillator, a novel 3D scintillation detector is proposed for precise acquiring the X, Y and Z interaction coordinates.

Speaker: Yang Shao (Novel Device Laboratory (NDL), School of Physics and Astronomy, Beijing Normal University)

Coffee Break

Astroparticles, Astrophysics and Astronomy

14 Calibration method for the non-linearity in the response of 20-inch PMTs in the JUNO experiment

The Jiangmen Underground Neutrino Observatory (JUNO) is a 20-kiloton liquid scintillator detector, currently under construction in Jiangmen, China. JUNO will be equipped with 17,612 20-inch photomultiplier tubes (PMTs) and 25,600 3-inch PMTs, and it will undertake a wide range of physics programs, including the observation of reactor, atmospheric, solar, geo, and supernova neutrinos, as well as searches for new physics. Among these, the primary physics goal is to precisely measure the neutrino oscillation parameters, including the neutrino mass ordering, from the energy spectrum of reactor neutrinos, with an energy scale uncertainty controlled within 1% and an energy resolution of 3% at 1 MeV. Achieving this objective requires a thorough understanding of the non-linearity and non-uniformity of the energy scale. Given that the number of observed photoelectrons per 20-inch PMT in reactor neutrino events in the JUNO detector varies from a single photoelectron to over 100 photoelectrons, calibrating the non-linear response of the 20-inch PMTs using the 3-inch PMTs, which are expected to observe significantly fewer photoelectrons due to their smaller size, is crucial to achieving these goals. This talk will introduce the calibration strategy, the key calibration system employed for this purpose, and the expected calibration quality based on the JUNO detector simulation.

Speaker: Dr Akira Takenaka (Shanghai Jiao Tong University, Tsung-Dao Lee Institute)

15 The Plastic Scintillator Detector for the future High Energy cosmic-Radiation Detection facility on board the Chinese Space Station

The High Energy cosmic-Radiation Detection (HERD) facility, located on board the Chinese Space Station, is expected to make significant advancements in cosmic-ray observations, dark matter searches, and gamma-ray astronomy, thanks to its innovative design. The HERD geometry is based on a 3-dimensional imaging calorimeter, which is surrounded on five sides by a fiber tracker, a plastic scintillator detector (PSD), and a silicon charge detector. This unique configuration enables HERD to address key questions in high-energy astrophysics with unprecedented sensitivity and resolution .

The PSD serves as an anti-coincidence system for precise gamma-ray detection (charged particle veto) and charged cosmic-ray nuclei identification. In order to achieve high performance in terms of detection efficiency and charge resolution, the PSD requires a highly segmented geometry, as well as the optimization of the light sensors and electronic read-out. The current design consists of long trapezoidal scintillator tiles coupled to Silicon Photomultipliers (SiPMs).

Different prototypes have been built and tested at CERN, Switzerland, and at the CNAO (Centro Nazionale di Adroterapia Oncologica) facility in Italy to study and improve the performance of the PSD. In this contribution, we present the overall project design and the PSD performance, with a focus on the nuclei identification capability.

Speaker: Fabio Gargano (INFN, Bari (IT))

16 The Analog Photon Processor ASIC

Full waveform digitization is an obvious solution for many particle physics detectors: Nyquist sampling ensures no information is lost, and extraction of important features can be postponed to later offline analysis, or can even be done by a fast FPGA before storage to disk. For large-scale photon detectors used in neutrino physics, however, the dynamic ranges run from just single photons to perhaps a few thousand per channel, and we are interested only in the number of photons each sensor detected and their arrival times. I will describe here an "Analog Photon Processor" (APP) ASIC, being designed for the TSMC 65 nm process, that extracts the features necessary to do precision photon counting and time measurement, even in the case of multiple photons piled up on a single waveform. The APP does this by fast analog measurements, thus significantly reducing data volumes and cost. The APP will be particularly useful for future detectors, such as the proposed Theia hybrid Cherenkov/scintillation detector.

Speaker: Joshua R Klein (University of Pennsylvania (US))

17 Development of an imager with high time resolution optical photon counter

Astrophysical sub-millisecond time-scale transient phenomena, such as fast radio burst and giant radio pulses from the Crab pulsar, have been observed in radio wavebands, although their origins are still unknown. To reveal them, a photon detector with high sensitivity and high time resolution is required. Recently, we have developed Imager of MPPC-based Optical photoN counter from Yamagata (IMONY), an observation system using a Geiger-mode avalanche photodiode (GAPD) as a sensor. The sensor is composed of 64 pixels, each of which is a combination of a GAPD and a quenching resistor, and its pixel sizes are 100, 150, and 200 um. The signal of each pixel is read out independently, and the sensor can detect a single photon. In a readout board, the output signal from the sensor is amplified and converted into the timing pulse by onboard comparators. Then, using a Global Navigation Satellite System (GNSS) and a Field Programmable Gate Array (FPGA), our system gives time stamp for each detected photon with a resolution of 100 ns. FPGA transfers the acquired data to a PC via Ethernet. We have conducted performance verification by observing the Crab pulsar which emits pulses with a period of 34 ms. This observation was made with two telescopes in Japan: the 1.5 m Kanata Telescope and the 3.8 m Seimei Telescope. We will present this system details and configuration with selected results.

Speaker: Anju Sato (Yamagata University)

18 Photodetector system of the JUNO experiment

Jiangmen Underground Neutrino Observatory (JUNO) is a 20-kiloton liquid scintillator detector currently under construction in Jiangmen, China. Situated 52.5 km from two nuclear power plants within a newly established 700-meter-deep underground laboratory, JUNO aims to determine the neutrino mass ordering by precisely measuring the energy spectrum of reactor neutrinos. Achieving this goal requires an energy resolution better than 3% at 1 MeV, along with an absolute energy scale uncertainty of less than 1% across the entire reactor antineutrino energy range. To meet these stringent requirements, the central detector (CD) will be equipped with 17,612 20-inch and 25,600 3-inch photomultiplier tubes (PMTs), achieving a total photocathode coverage of 78%. The CD is surrounded by a water Cherenkov detector instrumented with 2,400 20-inch PMTs. The large PMTs are interfaced with high-speed, high-resolution sampling electronics positioned close to the PMTs, while the smaller PMTs are read out using CATIROC ASICs. This presentation will discuss the JUNO photodetector system, highlighting performance results obtained from prototype modules and during the mass production of the final PMTs and readout electronics.

Speaker: Stefano Dusini (Universita e INFN, Padova (IT))

Poster Session

19 Latest MPPC developments from Hamamatsu

Hamamatsu Photonics K. K., a major manufacturer of the Multi-Pixel Photon Counter (MPPC), which is also known as Silicon-photomultiplier (SiPM), has developed technologies that are capable of detecting photons across a wide range of wavelengths. These solutions are capable of serving a multitude of applications such as calorimetry, TOF measurements, RICH/DIRC, etc. thanks to novel fabrication techniques and device structure enhancements that have led to finer time resolution, increased SNR, expanded dynamic range, and improved radiation hardness, amongst other advancements. By achieving these results and continuing our R&D efforts, we hope to extend valuable benefits to the experimental physics community's endeavors of discovery.

Speaker: Ardavan Ghassemi (Hamamatsu Photonics USA)

20 RayQuant

Rayquant Technology Co., Ltd. is a high-tech enterprise specializing in single-photon detection and ultra-low-light imaging technology. The company is dedicated to delivering high-performance photon detection and single-photon imaging chips, modules, and systems, alongside comprehensive technical services and solutions for low-light detection applications. Through continuous technological innovation, Rayquant's high-performance SiPM chips have been widely applied in areas such as PET/CT medical imaging, fluorescence detection, security systems, high-energy physics, and environmental monitoring. This presentation will showcase the latest advancements in Rayquant's CMOS SiPM product development.

Speaker: Lao Hui

21 Exhibitors

Exhibitors

• Lao Hui, Yuexuan Hua (RAYQUANT Technology Co., Ltd)
• Marco Locatelli (CAEN)
• Shayan Gaeni (Testforce)
• Ardavan Ghassemi (Hamamatsu)
• MA, Lishuang (North Night Vision Technology(Nanjing)Research Institute Co., Ltd.)
• Yueling CHEN (North Night Vision Technology(Nanjing)Research Institute Co., Ltd.)

22 Impact of external radiation on dark rate noise measurement for the Hyper-Kamiokande photomultiplier tube

The Hyper-Kamiokande (HK) is a next-generation neutrino experiment built in Japan and scheduled to begin operation in 2027. A new PMT has been developed for the HK water Cherenkov detector with modifications in detection efficiency, timing resolution, and pressure tolerance by a factor of two with respect to those used in the Super-Kamiokande detector. The HK detector will be instrumented with 20,000 photomultiplier tubes (PMT). Currently, the PMTs are produced, and the performance testing of the delivered PMTs is underway in parallel. In this test, it was observed that the dark rate values differed depending on the measurement location. The difference is due to environmental radiation, which was confirmed by a test with a radiation source. This poster presents a correlation between the irradiation of gamma rays and dark noise rate and the evaluated intrinsic dark noise rate of HK PMT after subtracting the contribution due to environmental radiation.

Speaker: Mr Yuta Mandokoro (Tokyo University of Science)

23 Studies on variability and localization of dark count in silicon photomultipliers

Silicon photomultipliers (SiPMs) are widely used in photon counting experiments today because of their high photon detection efficiency, compactness, small dead area, and low bias voltage. However, SiPMs tend to have higher dark count rate than conventional photomultiplier tubes, and their temperature dependence is known to be non-negligible. Therefore, it is essential to characterize and calibrate the dark count rate to accurately extract the charge of faint signals. In previous studies, the SiPM dark count rate was usually measured only on short time scales of minutes to hours, and its long-term instability was not discussed. In the present study, we monitored dark current of 128 SiPM channels, which is nearly proportional to the dark count rate, for about a year to find any unexpected failure modes before the construction of the next-generation ground-based gamma-ray observatory, the Cherenkov Telescope Array Observatory, which will use on the order of $ 10^5 $ SiPM channels to detect atmospheric Cherenkov photons. Through this study, we found that the dark current baselines of 50 of the 128 channels frequently changed by 5-20% on time scales of hours to days. We investigated the cause of this multimodal behavior in detail by observing the photon emission from the SiPM surfaces and correlating the brightness change with the dark current. We conclude that multiple avalanche photodiode (APD) cells of a single SiPM carry this baseline change, because certain APD cells were bright in optical images (hot spots) when the dark current shifted to higher baselines. While the dark current shift of up to ~20% is not a problem for gamma-ray observations under the night sky, understanding the cause of the hot spots will be able to reduce the dark current of future SiPM products. In addition, photon counting experiments under very dark conditions might improve the charge resolution by taking into account the dark current instability we found.

Speaker: Akira Okumura (Nagoya University)

24 New developments in VUV photo-detection

Noble element Time Projection Chambers are cutting edge detectors in high energy physics, their use spanning across fields from neutrino to dark matter to neutrino-less double-beta decay experiments. Whereas the charge collection is a well-understood process, improving the light collection is key to enhance detection sensitivity. Noble elements (Xenon and Argon) scintillate in the deep VUV (128 and 178 nm). Improvements in the detection technologies for these challenging wavelengths are required for next generation experiments to reach their physics goals. In this talk, an overview of different approaches being studied in the University of Manchester is presented, including new semiconductor materials, metallenses and coatings.

Speaker: Miguel Angel Garcia Peris (University of Manchester)

25 Calibrating the photometric performance of a high-time-resolution photon-counting imager for optical astronomy

Optical observations with high time-resolution should be a key to understand the origin of sub-millisecond time-scale astronomical phenomena such as giant radio pulses from the Crab Pulsar. We have developed a high-speed imaging system, Imager of MPPC-based Optical photoN counter from Yamagata (IMONY), using a customized Multi-Pixel Photon Counter (MPPC) as a sensor. This sensor is designed to read out signals from all the 8x8 pixels independently and to work as an imager of Geiger-mode avalanche photodiode array. We installed IMONY on the 3.8 m aperture Seimei Telescope in Okayama, Japan. We have successfully detected the 34-ms period of the Crab pulsar and imaged stars in the sensor's field of view. However, we have also found a small fraction of the pixels showed double or multiple pulses that used for the photon arrival timing. This situation should be due to circuit noise and unfortunately may result in overestimating the number of photons detected. In order to precisely estimate the photon flux of targets or the sky background, calibration of such over-counts is important. We measured the number of detected photons relative to the light intensity of each pixel in a laboratory environment. The number of overestimated counts is estimated based on the Poisson distribution of the time lag between each hit pulse. After applying the calibration to the observed data, we confirmed the linearity that is the correlation between magnitude and the number of detected photons. We will present the calibration and evaluation of the IMONY's photometric performance.

Speaker: Mana Hasebe (Yamagata University)

26 Development of a Cost-Effective RICH Detector for MARQ Spectrometer Using SiPM Technology

We are developing a Ring Imaging Cherenkov (RICH) detector for the MARQ spectrometer at J-PARC’s Hadron Hall, specifically designed for particle identification in the momentum range of 2-18 GeV/c. The detector, with dimensions of 4x6x2 m³, employs a dual-radiator configuration, combining Aerogel (n=1.04) and C3F8O gas (n=1.00137), to discriminate among scattered particles such as pions, kaons, and protons/antiprotons. A key feature of our design is the use of Silicon Photomultipliers (SiPM), chosen for their significant cost advantage over traditional photomultiplier tubes.

Despite SiPM’s benefits, they present notable challenges, including a limited sensitive area and a high dark count rate. To mitigate these issues, we are integrating a light concentrator and a thermoelectric cooling system supported by a water chiller to regulate the SiPM's temperature at approximately 0°C or below. This innovative approach aims to enhance the detector’s performance while maintaining a low production cost, making it the most economical option in its class.

Our development represents a significant step toward building high-performance particle detectors using cost-effective and scalable solutions, offering a versatile tool for future experiments at J-PARC and beyond.

Speaker: Ken Suzuki (RCNP, Osaka-U)

27 Production and Performance of mPMT Modules for the Water Cherenkov Test Experiment

The Hyper-K experiment employs a near detector to measure and study neutrino interactions approximately 1 km downstream from the production point, where the oscillation effect is negligible. This detector is known as the Intermediate Water Cherenkov Detector (IWCD). A new detector technology called the multi-PMT (mPMT) has been developed due to its better timing and spatial resolution compared to the 20-inch Photomultiplier Tubes (PMTs) used in the Super-Kamiokande or Hyper-Kamiokande (Hyper-K) experiments. Hyper-K and IWCD will utilise mPMTs as their primary photon detection systems. Currently, the Water Cherenkov Test Experiment (WCTE) with a 40-ton water tank is under construction at CERN and will serve as a testbed for the IWCD. An mPMT optical module - a water-tight vessel containing 19 3-inch PMTs with readout electronics, offers several advantages, including enhanced granularity, weak sensitivity to Earth’s magnetic field, and more. A total of 100 mPMTs have been produced for use in WCTE, and based on their performance, approximately 300 additional mPMTs will be produced for the IWCD. This presentation will provide a detailed overview of the novel assembly procedures developed for constructing these mPMT modules, along with comprehensive information about the mechanical and electronic components used. Additionally, we will present a production summary of the mPMTs for WCTE and discuss the challenges encountered and how they were overcome during development.

Speaker: Mohit Gola (TRIUMF (CA))

28 Multilayer Coating Simulations for Enhanced Photon Detection in Particle and Astroparticle Physics

Photon detection efficiency (PDE) is a critical parameter in semiconductor and vacuum photodetectors used in particle and astroparticle physics experiments. Enhancing PDE in the relevant wavelength range and suppressing background photons are essential for optimizing experimental performance. Reflectance and transmittance at the photodetector surface, typically estimated using Fresnel's law, are key factors influencing PDE. However, the actual surface of silicon photomultipliers (SiPMs), particularly those without resin coating, resembles a multilayer structure due to the presence of SiO₂ and Si₃N₄ layers, making a simple two-media boundary model insufficient. To accurately model and improve SiPM PDE across different wavelengths, simulations of interference effects are required. Beyond photodetectors, multilayer coatings are also applied to other optical components such as Winston cones and telescope mirrors, which are crucial for detecting more signal photons, such as blue Cherenkov photons. These simulations necessitate the integration of both photon tracking (ray tracing) and multilayer analysis. While Geant4 and ROOT-based simulator for ray-tracing (ROBAST) are widely used for optical photon tracking in this field, they lack built-in multilayer simulation functionality. To address this gap, we have extended ROBAST to incorporate multilayer simulation capabilities, enabling unified ray-tracing and multilayer analysis within a single framework. This contribution presents the newly developed functionality in ROBAST and provides simulation examples from gamma-ray and cosmic-ray telescopes.

Speaker: Dr Akira Okumura (Nagoya University)

29 Time-of-flight measurement with the ALPHA-g Barrel Scintillator detector for gravitational studies of antimatter

The ALPHA-g experiment recently made headlines for the first direct measurement of the gravitational free-fall of anti-hydrogen. Crucial to this milestone is a detector system capable of accurately recording the vertical position of annihilating anti-atoms, with two critical requirements: precise localization of anti-hydrogen annihilations into the “up” or “down” regions, and effective discrimination against the cosmic ray background. To accomplish this, charged pions produced in the annihilation are tracked using a radial time projection chamber detector, and fitted to a common vertex. These pions are also detected by the “Barrel Scintillator” detector, composed of 2.6-meter plastic scintillator bars with silicon photomultipliers at both ends. The arrival time of photons at the silicon photomultipliers is used to determine the time of the pion hitting the bar. This timing information is then used as part of a multivariate analysis to reject externally incident cosmic rays. This poster showcases the time calibration procedure used to obtain time-of-flight measurement of cosmic rays in the Barrel Scintillator, and the background rejection algorithm that will be used for forthcoming ALPHA-g measurements of the gravitational behaviour of anti-hydrogen.

Speaker: Gareth Smith (TRIUMF)

30 Characterization of Silicon Photomultiplier Photon Detection Efficiency at Liquid Nitrogen Temperature

Silicon photomultipliers (SiPMs) are being used by many rare-event search experiments to read out scintillation light from liquid noble detectors due to their single-photon resolution. Knowledge of the photon detection efficiency (PDE) of these SiPMs is a critical input for modeling these detectors' light responses and optimizing their sensitivities for new physics; however, the PDEs of SiPMs are not well characterized at the cryogenic temperatures at which many experiments operate them. Measurements of the PDE at cryogenic temperatures are difficult, as they require an apparatus that is capable of changing a SiPM's temperature while holding all other optical properties constant. In this talk, we detail the design of a cost-effective test stand that has measured the PDEs of off-the-shelf, visible-light-sensitive Hamamatsu S13360-3050C and KETEK PM3325-WB-D0 SiPMs at liquid nitrogen temperature. We find that the PDEs for green-light wavelengths decrease from their room temperature values by roughly 20% for both devices across all measured overvoltages. Numerous systematic studies were performed to ensure that all optical properties of the test stand were temperature-independent and that the decrease in PDE originated solely from the cryogenic cooling of the SiPM.

Speaker: Sam Borden (University of Washington, CENPA)

31 Competition between Increasing and Decreasing Effects of the Afterpulsing Rate of PMTs during Night-Sky Observations

Photomultiplier tubes (PMTs) are crucial in photon-counting experiments due to their high detection efficiency and low noise levels. A key application is in imaging atmospheric Cherenkov telescopes (IACTs), which observe Cherenkov light from air showers triggered by high-energy gamma and cosmic rays. They are also employed in the Large-Sized Telescopes (LSTs) and the Medium-Sized Telescopes of the Cherenkov Telescope Array Observatory (CTAO), the latest-generation IACTs currently under construction. The LSTs are optimized for relatively low-energy observations, particularly in the range of 20 GeV to 150 GeV, requiring PMTs with extremely low false-signal pulsing rates to avoid data acquisition issues. Currently, only the first LST (LST-1) is in operation among the CTAO telescopes.

Afterpulsing in PMTs, caused by ionized gas molecules from accelerated electrons (mainly triggered by night-sky photons), generates false signal pulses. To address this, CTAO and Hamamatsu Photonics K.K. developed novel PMTs (R11920-100 for LST-1 and R12992-100 for subsequent telescopes) with an exceptionally low afterpulsing rate of less than 2 × 10^-4 per photoelectron input.

However, the afterpulsing rate increases over time due to atmospheric molecules, particularly helium, penetrating the tube. This increase, measured at roughly 3 × 10^-5 per year, could degrade the LSTs’ energy threshold over their 20-year operation. Conversely, we found that the afterpulsing rate decreases when PMTs are operated under high voltage with light exposure, a condition naturally met during IACT observations.

In 2023, we removed several PMTs from LST-1. These tubes were installed shortly before or after the telescope’s first light at the end of 2018. Our laboratory measurement showed no increase in afterpulsing compared to pre-installation measurements from 2015, suggesting that the decreasing effect quickly cancels the increasing one during operation. In this talk, we report detailed results and discuss the mechanisms behind this behaviour.

Speaker: Dr Mitsunari Takahashi (ISEE, Nagoya University)

32 Optical Surface Reflectivity Characterization in Water Cherenkov Detectors: Methodologies and Industrial Applications

Understanding the optical properties of various components in water Cherenkov neutrino experiments is essential for accurate detector characterization, which is critical for precise measurements. Of particular importance is the characterization of surface reflectivity within the Cherenkov volume. I will present a methodology for surface reflectivity characterization using a goniometer setup, addressing the challenges associated with measurements in both air and water (or other optical media). Additionally, I will discuss the broader implications of Bidirectional Reflectance Distribution Function (BRDF) measurements using a goniometer, including their industrial applications.

Speaker: Deepak Tiwari (Institute for Basic Science (KR))

33 Towards a New Scintillating Fibre Beam Monitor for the CERN North Area

The CERN Beam Instrumentation Group has developed a new scintillating fibre beam profile monitor for the secondary beam lines of the CERN North Experimental Area. This innovative monitor employs plastic scintillating fibres, read out with silicon photomultipliers, to provide a cost-effective and efficient solution for beam profiling. The design goals for the new monitor included ease and low cost of production, achieving a particle detection efficiency above 95%, compatibility with beam intensities ranging from 1 to 10^8 particles per second, a spatial resolution of 1 mm, a low material budget, coverage of an active area of 20 cm x 20 cm, operability in a vacuum environment, and equipped with in/out motorisation for retracting the equipment from the beamline. A prototype was tested at the CERN East Area facility, demonstrating excellent performance and validating the design for mass production.

Speaker: Inaki Ortega Ruiz (CERN)

34 Radiation hardness and annealing study of neutron-irradiated silicon photomultipliers

Silicon photomultipliers (SiPMs) are semiconductor photodetectors increasingly used in high-energy physics experiments. In the planned upgrade of the Large Hadron Collider beauty (LHCb) experiment, they are considered to be used to detect Cherenkov photons in the Ring Imaging Cherenkov (RICH) detectors. In this application, the biggest drawback of current SiPMs is their susceptibility to radiation damage, where the dark count rate (DCR), typically on the order of 10⁵ Hz/mm² at room temperature, significantly increases proportionally with the irradiation fluence, which hindered the single photon detection beyond 10⁹ neq/cm². In this contribution, 3 x 3 mm² SiPMs of different cell sizes and producers, Hamamatsu (50 μm), Ketek (25 μm and 50 μm), Broadcom (50 μm), AdvanSiD (40 μm), and SensL (35 μm) as well as 1 x 1 mm² SiPMs from SensL (35 μm) and FBK (15 μm), were characterized. The SiPMs were irradiated at the Jožef Stefan Institute TRIGA nuclear reactor with fluences from 10⁹ neq/cm² up to 10$^{13}$ neq/cm². The main objective was to determine the temperature at which irradiated SiPMs can still be useful in future RICH detectors. Besides, it was explored how the high-temperature annealing can improve the SiPM performance post-irradiation. For the SiPM characterization in all the cases, current-voltage (I-V curve) measurements, DCR measurements, and waveform analysis, including single photon time resolution (SPTR), were carried out at different controlled temperature steps from room temperature down to the liquid nitrogen temperature.

Speaker: Dania Consuegra Rodríguez (J. Stefan Institute)

35 EQR SiPM with Pulse Pile-up Resolving Algorithm for Enhancing Photon Counting Capability Aiming at PCCT Applications

Photon Counting CT (PCCT) is recognized as the future direction for X-ray CT development. The main stream of PCCT technology is based on X-ray direct-conversion detector, such as CdTe and CdZnTe (CZT) detectors. SiPM-based scintillation photon counting detectors (PCDs), which detect X-ray indirectly, are regarded as a cost-effective alternative. However, the pulse pile-up, resulting from high X-ray photons flux and prominent fluorescence lifetime of scintillator significantly restricts the counting rate of SiPM-based scintillator PCDs and blocks its practical application in PCCT.
In order to resolve this problem, we investigate a silicon photomultiplier with epitaxial quenching resistors (EQR) in conjunction with pulse pile-up resolving (PPR) algorithms in this study. The EQR SiPM, with a small active area of 0.52×0.52mm2, features a small microcell pitch of 10 μm and high fill factor of 49% leading to an adequate high photon detection efficiency (PDE) of 33% while retain large dynamics of 2684 microcells. Its recovery time is extremely fast, down to 1.1 ns due to both the small microcell and active area of the device. Under X-ray irradiation at 80 kV tube voltage, the PCD, composed of the EQR SiPM with a LYSO scintillator, demonstrated a record high X-ray photon counting rate more than 40 Mcps/mm2 when adopting a PPR algorithm, showing the EQR SiPM based scintillation PCDs have the potential to be applied in PCCT.

Speaker: Yongqiang Yan (Novel Device Laboratory (NDL), School of Physics and Astronomy, Beijing Normal University)

36 Development and evaluation of high-resolution gamma camera for animal imaging

Recently, $\alpha$-ray emitting radionuclides, which can treat cancer locally and effectively, have been attracting attention in the in the field of nuclear medicine. Among these, At-211, which is produced in cyclotrons in Japan, is particularly promising. Therefore, it is important to visualize the distribution of At-211 in vivo during targeted radioisotope therapy.
Currently, human SPECT is used for At-211 imaging in animal studies, with a typical resolution of approximately 5 mm. However, the resolution is insufficient for animal imaging experiments because of small sample sizes. Therefore, we developed a high-resolution gamma camera for mouse imaging. We fabricated a device comprising a 5 $\times$ 5 cm$^2$ multi-pixel photon counter (MPPC) array and 0.5 mm pitch diced GAGG scintillator array. A resistor-split substrate was installed behind the MPPC, and a center-of-gravity calculation was performed using the signal values recorded at the four ends, enabling us to develop a compact detector.
Here, we targeted 79 keV X-rays emitted by At-211. Therefore, we experimented with 81 keV $\gamma$-rays from Ba-133, which have a similar energy. By applying a correction method for image distortion and source intensity, a resolution of 0.6 mm was achieved. Additionally, a camera capable of imaging the entire mouse body is necessary to track drug dynamics. Therefore, we developed a large MPPC of 10 $\times$ 10 cm$^2$ and are working to expand the device while maintaining the resolution. We have succeeded in imaging an 81 keV of the Ba-133 source using this MPPC and planned further imaging and resolution evaluations.

Speaker: Ms Yuka Kikuchi (Waseda University)

37 Modeling of AlInAsSb waveguide avalanche photodiodes for MWIR applications

Mid-wave infrared (MWIR) photodetectors are obtaining increased market demand in various application fields such as sensing, spectroscopy, medical diagnostics, and communication systems. The application scope is also being expanded due to the integration ability for these devices into the silicon platforms. Although the MWIR avalanche photodiodes (APDs) have been developed and reported by several laboratories, challenges are still remained on reducing the signal-to-noise ratio, enhancing the quantum efficiency and improving bandwidths etc. These goal-oriented tasks are very challenging especially due to the internal impact ionization mechanism, the structure and material complexity, and the routine design trade-off issues among all the device performances. Therefore, modeling of such MWIR APDs as well as the relevant software package are highly requested to save the development time and cost. In this work, two-dimensional modeling of MWIR AlInAsSb waveguide APDs operating at 2 micrometer is presented. The edge-butt waveguide coupling is investigated based on the beam propagation method. The APD impact ionization and photon-electronic behavior are further simulated based on a drift-diffusion theory. The frequency response and bandwidth are also evaluated. Modeling results of I-V curves, multiplication gain, breakdown voltage, excess noise factor, -3dB bandwidth and gain-bandwidth product are presented with some comparable to the experimental report from other researchers. The bandwidth results are analysed and discussed with clues for further improvement.

Speaker: Dr Yegao Xiao (Crosslight Software Inc)

38 Response of the 20” Super-K PMT in Magnetic fields of up to 500mG

Super-Kamiokande (SK) is 50kT water Cherenkov neutrino detector composed of approximately 11,000 20” Photomultiplier Tubes (PMTs). Magnetic fields are understood to affect photoelectron trajectories through the bulb of large-sized PMTs, and consequently can affect their performance. As SK moves towards a systematically limited future, it is becoming increasingly important to understand the impact of residual magnetic field effects on PMT performance. The Photosensor Test Facility (PTF) at TRIUMF is a testbed designed to characterize the response of PMTs in various magnetic field configurations. Here we present new results investigating the gain, detection efficiency, and timing response of the 20” SK PMT in magnetic fields of up to 500mG. We also present simulation studies carried out in GEANT4 and Comsol to investigate the optical effects on photon-absorption and the magnetic field effects on photoelectron trajectories in the PMT bulb and dynode in differing magnetic fields.

Speaker: Dr Benjamin Smithers (TRIUMF)

Wednesday 20 November

Digital Photosensors

39 Overview of 3D Integrated Photon-to-Digital Converters for Particle Physics and Medical Imaging

The advent of Silicon Photomultipliers (SiPMs) has significantly enhanced radiation detection instrumentation, gradually replacing Photomultiplier Tubes (PMTs) in various applications. SiPMs have notably improved performance in timing-critical applications. However, their typical analog readouts face limitations, such as high power consumption, and challenges in signal integrity associated with digitization.

Our group proposes to leverage the Boolean nature of Single-Photon Avalanche Diodes (SPADs) in SiPMs to maintain the readout entirely in the digital domain, hence the term Photon-to-Digital Converter (PDC). This approach enhances the timing resolution of SPAD arrays by individually digitizing their output and actively quenching them. The SPADS can therefore be configured with different hold-off and recharge times to optimize detector performances.

PDCs are 3D integrated devices featuring a dedicated SPAD layer atop a CMOS readout ASIC, maximizing both photosensitive area and signal processing capabilities. We are collaborating with Teledyne Dalsa, an industry leader in MEMS and CCD fabrication, and using TSMC for CMOS wafers. By using major industry leaders we secure the path from conceptual to production-ready state-of-the-art PDCs, a critical aspect for next-generation experiments requiring large-area photon detection systems. An overview of the fabrication process will be presented at the conference.

We seek collaborators willing to learn to use our technology, with our support, in various contexts and applications. We wish to find early adopters with whom we can interact to maximize physics outcomes and get feedback on the technology and its next developments. We hope to share our ready-to-use comprehensive scalable test platform, enabling broader dissemination of the PDC technology to a broader user base as was seen in the advent of SiPMs 15 years ago.

This contribution will present the architecture and results of our PDCs and compare our 3D integration technology with other work in the literature.

Speaker: Gabriel Lessard (Université de Sherbrooke)

40 FBK roadmap towards the next-generation of 3D-integrated SiPM and SPAD technologies

Modern Silicon Photomultiplier technologies have achieved remarkable performance in several fields, ranging from medical imaging to Big Physics experiments to industrial applications. On the other hand, there are still several challenges in the SiPM and SPAD technology development. Among them, we can consider further improving the timing performance for Time-of-Flight PET and High Energy Physics experiments, increasing the sensitivity at short wavelengths below 200 nm, enhancing radiation hardness and building high-performance single photon imagers. Thanks to a recent upgrade of its microfabrication facilities, Fondazione Bruno Kessler (Trento, Italy) is currently working on 3D integration technologies, which could significantly improve the performance parameters cited above. We adopt a layered R&D approach, working in parallel on technology developments with different TRL. In addition to a more traditional, medium density TSV approach, FBK is working on a more advanced TSV concept, allowing independent, single cell connection without relevant loss of Fill Factor. Moreover, FBK has introduced a radical redesign of the microcell structure to build Backside-illuminated, NUV-sensitive SiPMs, potentially approaching 100% Fill Factor even with small cell size of 15 um. R&D and microfabrication of these technologies is ongoing and the first experimental results are expected in early 2024.

Speaker: Alberto Gola (Fondazione Bruno Kessler)

41 Digital SiPM Chip with High Fill Factor and Fully Integrated Serial Readout for Rare Photon Detection

Digital SiPMs combine Single Photon sensitive Avalanche Diodes (SPADs) and CMOS transistors on a single piece of silicon. The direct access to the large signal of an individual firing SPAD eliminates the need for analogue amplification and allows for disabling individual noisy cells, so that the overall dark count rate is greatly reduced. A readout scheme tailored to a particular application can be integrated so that no further electronics is needed and systems become mechanically simple, compact and low power. A design challenge is to keep the readout as basic as possible so that the area required for circuitry does not degrade too much the fill factor, i.e. the fraction of photo-sensitive area. We have developed a chip for the readout of randomly occurring photon signals with moderate rates targeted primarily for liquid scintillator experiments in fundamental physics, like DARWIN or XLZD. The chip with a size of $\approx 8\times 9\,\mathrm{mm}^2$ has a fill factor of above $72\%$, taking into account all readout circuitry, wire-bonding pads and chip edges. It is subdivided into $32\times 30$ pixels of $250\times 291\,\mathrm{\mu m}^2$ size. Each pixel contains $9$ SPADs which can be individually disabled, their hit signals are ORed together. The fully digital readout provides the x/y coordinates of hit pixels and a time stamp with $\approx10\,\mathrm{ns}$ resolution. Only power, SPAD bias and 4 CMOS signals are needed to operate a chip. A custom serial configuration and readout scheme allows for daisy-chaining a large number of chips. By the time of the conference, the chip should be back from production and we hope to present first measurements.

Speaker: Prof. Peter Fischer (Heidelberg University)

42 SiPM and CMOS SPAD characterization at liquid nitrogen temperatures

A number of high energy physics and cosmology experiments use or plan to use single-photon avalanche diodes (SPADs) or SPAD based silicon photomultipliers in harsh conditions, such as cryogenic temperatures and/or high radiation environments. In this contribution, studies of the operation of SPADs, front-end electronics, and micro-lens arrays at temperatures down to liquid nitrogen will be presented. SPADs designed by EPFL AQUA Lab in 180 nm, 110 nm and 55 nm CMOS technology were tested at different temperatures between room temperature and liquid nitrogen. The characterization included direct IV curve measurement and waveform analysis, in the dark, at low-light illumination, and in time-correlated single-photon regimes by way of picosecond lasers and monochromators. The most important quantities extracted were the single-photon time resolution (SPTR), dark count rate (DCR), and photon detection probability (PDP) at different temperatures. The SPADs and micro-lens structures, produced in technologies that could be applied to these SPADs, were also neutron irradiated with fluences up to 10$^{14}$ neutron equivalent/cm$^2$ and re-characterized after irradiation. The results of this study will be used to inform the photodetector design considerations in the planned Upgrade II of the LHCb ring imaging Cherenkov counter (RICH).

Speaker: Rok Dolenec (Jozef Stefan Institute (SI))

Coffee Break

Digital Photosensors

43 Current status and development of Digital CMOS SiPM for scintillator-based radiation detectors toward all-digital sensors

Modern scintillator-based radiation detectors require silicon photomultipliers (SiPMs) with photon detection efficiency > 40% at 420 nm, possibly extended to the vacuum ultraviolet (VUV) region, SPTR < 100 ps, and DCR < 150 kcps/mm2. To enable single-photon time stamping, digital electronics and sensitive microcells need to be integrated in the same CMOS substrate, with a readout frame rate higher than 5 MHz for arrays extending over a total area up to 4×4 mm2. This is challenging due to the increasing doping concentrations at low CMOS scales, deep-level carrier generation in shallow trench isolation fabrication, and power consumption, among others.

The presentation will first show an overview of the advances at 350 nm and 110 nm CMOS nodes, which will be benchmarked against available SiPMs obtained in other CMOS and commercial customized technologies. Experimental results of the newest CMOS SiPM realized at 110 nm, exhibiting a Photo Detection Efficiency of 61% at 420 nm, a dark count rate of 140 kcps/mm2, will be shown. Their application to radiation sensors will be also demonstrated through experimental results in LySO scintillator light readout.

Based on these CMOS nodes, the presentation will further describe the concept of digital multithreshold SiPMs, a new sensor realized at 110 nm and 350 nm CMOS nodes, including SiPM detection elements, single cell digitalization, and on-chip digital signal processing circuitry, aiming at a real-time readout and analysis of the light emitted by scintillators.Experimental results of the first sensor prototypes will be reported.

Speaker: Nicola D'Ascenzo (University of Science and Technology of China)

44 Overview of Fermilab ASIC Development in Photodetectors and Related Areas

Fermilab Microelectronics department has a strong effort in a number of areas. Traditionally, we focused on addressing the next challenge for High Energy Physics, including operation in extreme environments including cryogenic and radiation, including developments for DUNE and LHC and dark matter searches. In the last few years, we have expanded our portfolio to use the expertise gained in those areas to chips capable of single digit picosecond timing, AI-on-chip, support for quantum computing and quantum sensing as well as high speed photonics. Some of the highlights will include MIDNA and SPROCKET (readout of skipper CCDs), SParkDream (silicon photonics link at 10Gbps), efforts in cryogenic digital SiPMs and SNSPDs. We have also been developing a wide range of IP, including ADCs and DACs for 4K operation, and radhard/cryogenic Edge AI (using HLS4ML)

Speaker: Paul Michael Rubinov (Fermi National Accelerator Lab. (US))

45 A detector concept based on dielectrically coupled digital photo sensors

We present a novel detector concept using dielectrically-coupled photo sensors.
Our goal is to combine digital sensors with both power over fibre (PoF) and signal over fibre (SoF) to enable readout within electric fields (e-fields) at cryogenic temperatures. Motivated by maximising sensitivity of large-volume time projection chambers (TPCs). Timing resolution is limited by the optical path (Rayleigh scattering) and wavelength shifting. To mitigate these limitations, we need ultraviolet-sensitive sensors inside the active volume. Recent advancements in power over fibre have enabled instrumentation within e-fields. However, its efficiency limits channel density. We aim to reduce heating with pulsed power charging a capacitor integral to the sensor. To avoid issues associated with analog signal transmission and processing we require intrinsically digital sensors.

We define a digital photo sensor unit (DPSU) as a combination of a power over fibre receiver, an array of digital silicon photomultipliers, a signal over fibre receiver and transmitter, and associated electronics. Instead of augmenting existing TPCs with DPSUs, design a TPC around them. Consider a combination of IceCube and a TPC: IceCube has strings of photomultipliers embedded within a very large ice target mass. This can be applied to TPCs by extending strings of DPSUs between anode and cathode at separations below the Rayleigh scattering length, 0.9 m for argon, the DPSUs would have access to prompt local light, providing a TPC with unprecedented timing. Given sufficient sensor density, only timing information is needed.

Fast timing helps with energy resolution by improving the tagging of secondary, non-obviously-spatially-correlated, activity (e.g. neutrons), and identifying directionality (interaction vertex). It also enables particle identification through timing. The lack of waveform analysis for light data would simplify the DAQ and dramatically reduce computing requirements for large experiments.

We will present a development path for the components needed for such a detector and the status of our R&D.

Speaker: James Sinclair (SLAC National Accelerator Laboratory)

Lunch Break

Cryogenic and Noble Liquids Detectors

46 Light detection in Dark Matter and Neutrino Detectors

Particle detection and identification in astroparticle physics heavily rely on light detection. From dark matter searches to neutrino physics, the study of photons produced in particle interactions is crucial to further our understanding of these very precise detectors and to identify the rare signals they are looking for. After providing an overview of the light detection techniques in astroparticle detectors, I will discuss the challenges and the technological advances explored to increase the discovery potential of rare event searches experiments.

Speaker: Roxanne Guenette

47 Characterization of New VUV Silicon Photomultipliers with Low Dark Noise at Low Temperature

Silicon photomultiplier (SiPM) has a low radioactivity, compact geometry, low operation voltage, and good photo-detection efficiency for vacuum ultraviolet light (VUV). Therefore it is expected to replace photomultiplier tubes (PMTs) for future dark matter experiments with liquid xenon (LXe) such as DARWIN/XLZD. However, SiPM has nearly two orders of magnitude higher dark count rate (DCR) compared to that of PMTs at the LXe temperature, which is ~165 K. This type of high DCR mainly originates from the carriers generated by band-to-band tunneling effect. To suppress the tunneling effect, we have developed a new VUV SiPM with lowered electric field strength in cooperation with Hamamatsu Photonics K. K. and characterized its performance at LXe temperature. We demonstrated that the newly developed SiPMs had 5-7 times lower DCR at low temperatures compared to that of the conventional SiPMs, reaching 0.05 Hz/mm^2. In this presentation, details of the characterization will be presented.

Speaker: Prof. Shingo Kazama (Nagoya University)

48 The 'burst' phenomenon in SiPMs at liquid nitrogen temperature

Burst effect of Silicon Photomultiplier (SiPM) at cryogenic temperatures have been discovered few years ago looking at the dark count rate of SiPMs at liquid nitrogen temperatures. A burst consists in trains of consecutive avalanche events, characterized by a rate that is about 100 times that of the single-event uncorrelated dark counts, and results in an overall increase of the DCR. Burst events start typically with a high-amplitude event (> 4p.e.) and last for tents of millisecond. The number of events in the burst is typically ∼ 100 and the amplitude of events contained in the burst are distributed around the single photoelectron (p.e.). Bursts occurs in a few types of SiPM models of Hamamatsu Photonics K.K. (HPK) and Fondazione Bruno Kessler (FBK) when operated at liquid nitrogen (LN2) temperature.
In this work we describe a detailed study related to both the external causes that triggers bursts and to the phenomenon, internal to the sensor, that produces this dark signals. We related the burst occurrence to the luminescence produced by some trapping centers in the SiPMs when they are excited by ionizing radiation that impinges on the sensor.
To study the nature of trapping centers, further investigations are necessary in close synergy with vendors on material compositions and fabrication processes.

Speaker: Luca Tomassetti (Universita e INFN, Ferrara (IT))

49 Scintillation Imaging in GRAIN Liquid Argon Detector of DUNE experiment

GRAIN (GRanular Argon for Interaction of Neutrinos) is a Liquid Argon detector which is part of the Near Detector complex of DUNE experiment.
Most conventional noble liquid detectors employ scintillation light as either a timing signal for a TPC or as a calorimetric measurement, or both. Its relative amplitude and timing on multiple detectors can also be used to approximately locate an interaction.
In GRAIN we go a step further, by using scintillation light to reconstruct images of tracks associated to charge particles in Liquid Argon volume. In fact, by developing a suitable optical system, coupled with finely segmented SiPM arrays, it is possible to build photographic cameras that capture images of the primary scintillation light. In absence of a TPC, scintillation imaging alone can provide vertexing and tracking information, while combined it can enhance resolution and rate capability (which is a concern for near detectors located on powerful neutrino beams).
Argon scintillates in the VUV range, imposing stringent requirements on the optical system and SiPMs. By replacing a traditional set of lenses with a coded aperture mask, a thin and compact camera with both deep and wide field of view can be created, at the modest cost of additional offline processing.
The latest results from simulation and reconstruction of neutrino interactions in GRAIN LAr detector equipped with these cameras will be presented. In particular, the development of key enabling technologies, such as a large, low power cryogenic ASIC and VUV-enhanced Backside Illuminated SiPMs will be emphasized.

Speaker: Alessandro Montanari (Universita e INFN, Bologna (IT))

50 Recent results from the LUX-ZEPLIN (LZ) dark matter experiment

The LZ experiment, the largest liquid xenon time-projection chamber (TPC) built to date, continues to provide world leading sensitivity to WIMP dark matter candidates. In this talk, I will present the most recent results searching for WIMP dark matter from the combined 2022-2024 exposure. In addition to the increased exposure, the latest result showcases a number of refinements to LZ’s background modelling, such as a radon tagging analysis, that reduces the dominant background by 60%, and detailed modelling and in-situ measurement of charge attenuation of the rare decay of ¹²⁴Xe via double electron capture. Alongside the target mass and strict control of radiogenic backgrounds, the sensitivity of LZ and other dark matter detectors depends critically on achieving a low detector threshold. This talk will also cover how LZ has achieved a keV-level detection threshold, with a particular focus on the VUV photomultipliers and their readout.

Speaker: Albert Baker (King's College London)

51 Cryogenic SiPMs for the optical readout of DarkSide-20k

Silicon photomultipliers (SiPM) have gained significant traction as an alternative technology to the well-established photomultiplier tube (PMT), with numerous high-sensitivity experiments adopting them either complementarily or as a replacement for PMTs. SiPMs are an ideal match for low-background cryogenic applications, such as massive noble liquid experiments for dark matter direct detection, due to (i) the significant reduction of dark noise in cold environments, (ii) relatively low radioactive content, and (iii) scalable industrial production. For these reasons, the Global Argon Dark Matter Collaboration has committed to this technology for DarkSide-20k, currently under construction at LNGS Hall C. The development of a large-area cryogenic SiPM-based photon counter has culminated in the Photon Detector Unit (PDU), a compact photosensor measuring 20x20 cm² with 100 cm² active surface per channel, based on SiPM technology from Fondazione Bruno Kessler and incorporating custom front-end electronics suited for cryogenics. More than 600 PDUs are being produced and tested in various collaboration facilities to construct the two ~10.5 m² optical planes of the massive two-phase argon time projection chamber of DarkSide-20k and the optical readout of its veto system.

Speaker: Giuseppe Matteucci (Università degli Studi di Napoli Federico II)

Coffee Break

Cryogenic and Noble Liquids Detectors

52 Online Data Processing and Monitoring for DarkSide-20k

Liquid Argon (LAr) Time Projection Chambers (TPC)s are promising detectors for dark matter search, due to their response uniformity, scalability to large target masses, and suitability for extremely low background operations. The Darkside-20k (DS-20k) experiment is a new dark matter detector under construction at INFN LNGS that aims to push the sensitivity for Weakly Interacting Massive Particles (WIMP) detection down to the neutrino floor. Thanks to its size and sensitivity the detector will allow a broad physics program including supernova neutrino detection.

DS-20k will employ a triggerless Data Acquisition system (DAQ) that continuously captures signals from SiPMs-based photosensors. The expected interaction rate is about 100 Hz, with a dark count rate of approximately 20 Hz per channel (2720 in total). The DS-20k DAQ must be able to identify signals as small as 1 photoelectron with event rates as large as 200 Hz. Signals are digitized by 36 newly available commercial VX2745 CAEN 16-bit, 125 MS/s, high channel density (64 channels) waveform digitizers (WFD). The WFD data are read out by a set of Frontend Processors (FEP), which filter signal waveforms and reduce them by identifying hits before passing the data to the Time Slice Processor (TSP), where the whole detector data is assembled in fixed length time series, analysed and stored for offline use.

Moreover, live data monitoring is crucial during the detector run phase for ensuring data integrity, identifying anomalies, and optimizing detector performance. A prototype of the DS-20k monitoring system called "vertical slice" was developed at TRIUMF laboratory. It is fully integrated with a Maximum Integration Data Acquisition System (MIDAS) developed in the Paul Scherrer Institute in Switzerland and TRIUMF laboratory in Canada and will allow us to stress-test a fraction of the DAQ architecture, to test the digitizers readout, and the same diagnostics tools that will be used for DS-20k.

Speaker: Maria Adriana Sabia

53 nEXO Photon Detection System and Read-out Electronics

nEXO is a next-generation 5-tonne liquid xenon (LXe) time projection chamber that will search for the neutrinoless double beta decay (0νββ) of Xe-136, which is a lepton number violating process that can occur if neutrinos are massive Majorana fermions. The experiment has a projected half-life sensitivity of 1.35 x 10^28 years over 10 years of livetime, which sets a design goal of 0.8% energy resolution (σE/E) at the decay Q-value of 2.458 MeV. Achieving this goal requires stringent control of the radiopurity of detector materials while maintaining single photon resolution at the vacuum-ultraviolet scintillation wavelength of LXe of 175 nm. In this talk, I will describe the design challenges and novel solutions that have led to nEXO’s photodetection design, which will instrument approximately 4.5 m^2 with VUV-sensitive silicon photomultipliers (SiPMs) that are read out with cold electronics within the LXe. This talk will describe the individual SiPM performance and discussion of the readout architecture and custom ASICs that have been tailored to meet the experiment’s energy resolution goal, while achieving high pixelation to allow for background discrimination.

Speaker: Molly Watts (Yale University)

54 Modelling the photodetection efficiency of SiPMs from the near UV to the IR

We will present an experimentally verified model for characterising the photodetection efficiency of silicon photomultipliers (SiPMs). This work has been performed in the context of improving detector response for any SiPM based experiment requiring accurate photon simulations. The model is based on comprehensive measurements of photon detection efficiency for two UV sensitive Hamamatsu and FBK devices. Measurements have been under illumination from 350-900nm at various bias voltages, angles of incidence and temperatures. This permits a detailed description of optical transmission into the device, the internal junction structure, and the probabilities of charge carriers producing avalanches.

This model is a powerful tool to aid in assessing detector performance across a range of optical inputs and characterising optical cross-talk between SiPMs, as it can be generalized to a broad range of devices. In addition, we will discuss extensions to the model including temperature dependance, internal electron transport and surface microstructure effects. Lastly, this model can inform future device design, as we hope to show the possibility of producing a silicon SPAD with a photon detection efficiency close to unity.

Speaker: Austin de St. Croix

55 VUV-sensitive MPPC used in the liquid xenon detector for the MEG II experiment

The MEG II experiment searches for new physics like SUSY-GUT/SUSY-seesaw through the lepton flavor violating mu+ -> e+ gamma decay with ten times better sensitivity than the MEG experiment. The MEG experiment published the result of B(mu+ -> e+ gamma)<4.2x10-13 at 90% CL. in 2016, which was thirty times better result than the previous limit. While the MEG experiment utilized 846 2inch PMTs to detect scintillation light in 900L liquid xenon gamma calorimeter, 216 2inch PMTs on the gamma incident face are replaced with 4092 VUV-sensitive MPPCs (SiPMs produced by Hamamatsu) in the MEG II experiment to improve energy and position resolutions. We have started the physics data taking in 2021, and the first results were published in 2023. Here the LXe detector status including initial photon sensor calibration and performance will be summarized together with the current experimental status and the latest results. The PDE decrease of the SiPM observed in the high rate muon beam environment and our possible solution (annealing method) will also be discussed.

Speaker: Toshiyuki Iwamoto

56 LightPix: Scalable readout for silicon photomultipliers in cryogenic environments

LightPix is designed for amplification, triggering, digitization, and multiplexed readout of high-channel count silicon photomultiplier (SiPM) systems, particularly within cryogenic environments. It is based around the LightPix application-specific integrated circuit (ASIC), a custom low-power cryo-compatible ASIC which provides 64 input amplifiers, self-triggering TDCs with O(ns) precision, and digital multiplexed readout. The LightPix system leverages the scalable readout techniques and digital back-end components from the related LArPix effort, which has been demonstrated in multiple liquid argon detectors with >10$^5$ channels. LightPix also features programmable multi-channel hit-coincidence logic to mitigate high dark count rates, enabling applications beyond cryogenic detectors. Prototype detectors using the current LightPix ASIC will be presented, and progress on the design of the next-generation LightPix ASIC will be discussed.

Speaker: Stephen Greenberg (UC Berkeley)

Gala Dinner

Thursday 21 November

Timing

57 Study on the limited time performance of FPMT and SiPM under femtosecond laser

Photomultiplier tubes (PMTs) and silicon photomultiplier tubes (SiPMs) are advancing towards ultra-fast time resolution, high gain, and low noise, becoming highly sought-after photodetectors in the fields of medical imaging, bio-detection, and nuclear detection. To unveil the potential time resolution limits of ultra-fast PMTs(FPMT) and SiPMs, we will use a femtosecond laser as the light source to minimize the impact of pulse width on the time resolution of FPMT and SiPM, aiming to enhance the accuracy and precision of the experiments. Preliminary test results show that the ultimate time resolution of FPMT is less than 1 ps, which is an exciting result that will drive us to explore their time performance under extreme conditions, providing important insights for their applications in ultrafast optics, laser particle accelerators, biomedical imaging, and other fields.

Speaker: Lishuang MA

58 Next generation microchannel plate detectors for high spatial and temporal resolution

Multi-anode Microchannel Plate (MCP) detectors provide unique performance, especially with regards to sub 30ps timing resolution, signal photon sensitivity, and modular design. Developments for HEP applications such as the TORCH project, require increasing the photon rate capability and higher spatial granularity of existing designs.

These demands are being tackled in two ways, firstly by developing a higher granularity custom readout for the TORCH project of 16x96 (0.55 mm pitch), to enable their application in using Cerenkov radiation for partial identification. Secondly, for applications such as life science and medical imaging, a novel design has been established, utilising resistive sea technology to introduce charge sharing across multiple pads, thus improving spatial resolution (at the cost of occupancy) beyond the physical pitch of the anode readout.

To assess the performance of the novel detector readout, a series of characterization tests are detailed. These include measuring cross-talk to evaluate FWHM spatial resolution, analysing single pad pulse height distributions to determine gain, and timing single pad responses to assess Transmission Time Spread (TTS). Additionally, the study aims to evaluate the effect of image performance with different sample rates.

Developing charge sharing techniques achieves megapixel-scale spatial resolution by using a resistive layer for charge collection. A ceramic insulator between this layer and the anode spreads the charge across multiple pads via capacitive coupling, thus making spatial resolution independent of anode pad size. Within this configuration each ‘pixel’ of the anode is connected to a channel of the TOFPET2d electronics, which measures the timestamp and charge of all 256 channels individually. This research details results and optimisation methods of using this electronic readout to train neural networks to reconstruct single photons comparing the method to previous algorithmic techniques. Characterisation of the Resistive Sea MCP detector is discussed, including uniformity, timing and amplitude walk correction.

Speaker: Thomas Conneely (Photek LTD)

59 Ultrafast stimuation of single photon avalanche diodes with a broad spectrum light source

Silicon photon multipliers (SiPMs) are arrays of individual single photon avalanche diodes (SPADs). These devices have been under intense development for applications ranging from large-area particle physics experiments to industry applications such as LIDAR. Each application requires the device to be tailored to extract maximum performance. Using the Microscope for the Injection and Emission (MIEL) we seek to understand the foundational operating principles of SPADs and generate new models to develop better SiPM devices. MIEL is equipped with a broadband femtosecond OPA laser system (310-2700nm) which is used as a probe to understand SiPMs response to light. Additionally, two photon absorption using IR photons can be used to inject charge carriers at specified depths. MIEL is also equipped to measure the secondary emission of SPADs to understand external cross-talk, and potentially develop methods of mitigating internal cross-talk. This MIEL system is currently being used to characterize a digital SiPMs developed by UdeS. An update on the experimental capabilities and results of the MIEL setup will be shown.

Speaker: Seraphim Koulosousas

60 Development of a picosecond-timing Cherenkov detector using gaseous photomultiplification

Photosensitive gaseous detectors with a simple photoelectron multiplication mechanism as resistive plate chamber are expected to offer both large photocoverage and excellent time resolution while keeping costs low. We have developed a gaseous photomultiplier (GasPM) and demonstrated that a single-photon time resolution is $25 \pm 0.2$ ps at the gain of 3.3 $\times 10^{6}$ with a $\rm{LaB_{6}}$ photocathode, which has an extremely low quantum efficiency. With a CsI photocathode, GasPM can be used as a picosecond-timing Cherenkov detector. A possible application of this detector is the particle identification in the Belle II experiment, which is an electron-positron collider experiment searching for physics beyond the Standard Model through precise measurements of $B$, $\tau$, and $D$ decays. A picosecond-timing Cherenkov detector can enhance particle identification efficiency through precise time-of-flight measurements.
We developed a second prototype of GasPM with a $\rm{MgF_{2}}$ window as Cherenkov radiator and a CsI photocathode. A mixture of R134a and $\rm{SF_6}$ gases is used, and the gas gap size is 200 $\mu m$. We conducted the first beam test to evaluate the performance of this GasPM using the 3 GeV electron beam at the PF-AR test beamline located at KEK, Japan. We applied up to 2.8 kV across the gap, at which the single-photon time resolution estimated by simulation is $\sigma=60-70~\rm{ps}$, and verified that the time resolution was as expected. However, we observed a secondary avalanche caused by feedback photons from the primary avalanche, which degraded the time resolution due to the overlap of the two pulses. The time resolution can be improved by suppressing the effects of feedback photons and applying a higher voltage.

We will present these results and discuss the plans for the GasPM development and the future implementation at the Belle II experiment.

Speaker: Ryogo Okubo (Nagoya University)

Applications

61 Towards optical radiography: photon-detectors to look inside the body using light

For hundreds of years we have known that visible light can pass through human tissues, while for about fifty years we have also known that this offers incredible diagnostic and treatment opportunities. Among several applications, here we focus in particular on those requiring innovative photon detectors to push the actual barriers of laser based diagnostic tools, and in particular on time domain diffuse optics (TDDO), which is a non-ionizing, label-free, and non-invasive technique capable of probing highly scattering media like biological tissues using just visible and/or near-infrared sub-nanosecond light pulses. From the analysis of the tissue absorption and scattering spectra and of the speckle intensity fluctuations of coherent light, the technique allows one to derive information about tissue composition, microstructure, and microvascular blood flow. TDDO has already opened, but it is still stimulating, new perspectives in several medical fields spanning from oncology to neurology, as well as in various non-medical fields like the optical characterization of food or wood. From the photon detection point of view, in particular, TDDO is experiencing fascinating technology advancements, fostered by the unceasing evolution of single-photon avalanche diodes (SPADs), silicon photomultipliers (SiPMs), and superconductive nanowire single-photon detectors (SNSPDs), mostly in the framework of a running (fastMOT -G.A. 101099291-) and of some recently concluded EU H2020 projects. In this work, we will review the performances of nowadays cutting-edge photon detectors in this field, their inherent advantages that have enabled the evolution of diffuse optical imaging systems from table-top instruments to wearable systems, also enabling an unprecedented penetration depth inside human tissues (up to about 4 cm), as well as their remaining limitations in order to stimulate the research towards a perfect photon detector for time domain diffuse optics.

Speaker: Alberto Dalla Mora (Politecnico di Milano)

Coffee Break

Applications

62 Proposal and demonstration of a novel SPECT for high-precision gamma-ray imaging

In the field of nuclear medicine, there has been a growing demand for devices that can image gamma rays of several hundred keV. For example, radioactive gold nanoparticles have been proposed as ideal drug carriers that can be traced using their 412-keV gamma rays. However, devices offering high spatial resolution for imaging using such high-energy gamma rays have not yet been developed. Single-photon emission computed tomography (SPECT) uses an X-ray/gamma-ray imaging device equipped with a collimator that limits the arrival direction of X-rays and gamma rays. Although SPECT is widely used in clinical practice, it has two limitations. First, its typical spatial resolution is 5 mm, which is insufficient for use in animal experiments. Second, the energy of the X-rays/gamma rays that SPECT can image is below 200 keV because high-energy gamma rays tend to penetrate the collimator walls.
Therefore, we developed a novel SPECT capable of high-resolution imaging using high-energy gamma rays. To improve the spatial resolution, we used a 1-mm pitch array of Gd₃(Ga,Al)₅O₁₂(Ce) scintillators bonded with a multi-pixel photon counter array instead of a conventional photomultiplier tube. For imaging using high-energy gamma rays, we developed a novel collimator with an array of hourglass-shaped holes that were wide at the upper and bottom surfaces of the collimator and narrow in the middle. This hole shape offers thicker collimator walls while maintaining high sensitivity compared to the conventional parallel shape, enabling high-resolution imaging using high-energy gamma rays. In this study, we visualized radioactive gold in a Derenzo phantom using 412-keV gamma rays with a newly developed SPECT system. As a result, a 2-mm spatial resolution was achieved. In addition, we compare the new SPECT system with conventional SPECT and Compton cameras in the presentation.

Speaker: Ms Nanase Koshikawa (Waseda University)

63 Ultra-Low Resource Time-to-Digital Converter for PET TOF Systems Achieving Sub-10 ps Resolution Using LUT-Based Counter on FPGA

Positron emission tomography (PET) systems greatly benefit from precise timing measurements, especially in time-of-flight (TOF) applications, which enhance image quality by providing more accurate localization of positron annihilation events. Current commercial TOF systems typically require Time-to-Digital Converters (TDCs) with timing resolutions in the range of 10-20 picoseconds (ps) to achieve an overall coincidence timing resolution of around 200 ps in full width at half maximum (FWHM) between two PET detectors. These precise measurements are accomplished using TDCs. However, as the number of channels increases, particularly in total-body PET systems, the resource demands on FPGAs for TDC implementation grow significantly, leading to higher costs and reduced scalability.

Traditional FPGA-based TDCs rely on Tapped Delay Lines (TDLs) to achieve high-resolution timing. While effective, this approach necessitates the use of multiple TDLs to improve resolution, which significantly increases FPGA resource consumption and limits the number of channels that can be synthesized.

In this work, we propose an ultra-low resource TDC design that utilizes a Look-Up Table (LUT)-based counter as the time measurement unit instead of the conventional TDL approach. Our design achieves a sub-10 ps time resolution, which is comparable to existing TDL-based TDCs, but with a remarkable reduction in resource usage by around 60%. This significant reduction in FPGA resource consumption enables the implementation of more channels on a single FPGA, thereby maintaining system performance while also lowering costs.

Our proposed solution offers a viable path forward for scaling PET systems, particularly for total-body PET applications where the number of channels is a critical factor. By reducing FPGA resource usage while maintaining sub-10 ps timing performance, this method represents a valuable advancement in the development of cost-effective, high-performance PET TOF systems.

Speaker: Sun Il Kwon (UC Davis)

64 A Neutron Spectrometer for General Fusion

General Fusion is developing a prototype fusion machine under its Lawson Machine 2026 (LM26) program, leveraging the principles of magnetized target fusion. A key objective of LM26 is achieving an ion temperature of ≥10 keV, which presents significant challenges in accurate temperature measurement. To address this, a time-of-flight neutron spectrometer is proposed.
In deuterium-deuterium fusion reactions, monoenergetic 2.45 MeV neutrons are produced. However, the plasma's ion temperature causes a dispersion in neutron energy in the lab frame via the Doppler effect, with the standard deviation proportional to the square root of the ion temperature in keV. The proposed neutron spectrometer utilizes two layers of plastic scintillator coupled with Silicon Photomultipliers (SiPMs) to measure neutron energies. By recording the scattering angle and time-of-flight between interactions in the two scintillator layers, this setup should enable sufficiently precise neutron energy measurements to reconstruct the ion temperature.
Designing this spectrometer poses challenges due to the low total neutron count and high neutron incidence rate. Therefore, extensive modelling, simulation, and testing of the spectrometer’s position and timing sensitivity are crucial to ensure accurate plasma temperature measurements. Ongoing laboratory tests are focused on verifying that the selected detector materials and readout electronics meet the stringent requirements necessary for successful ion temperature measurements.

Speaker: Ryan Underwood (TRIUMF)

65 An Overview of Electronics, DAQ, and Monitoring in Reactor Neutrino Detectors

Reactor neutrino experiments are crucial for exploring fundamental questions in particle physics, including neutrino properties, oscillations, and interactions. This review provides a comprehensive analysis of advancements in electronics, data acquisition (DAQ), and monitoring systems that are essential for these experiments. Effective performance monitoring is vital for maintaining data integrity and accurate measurement of neutrino flux and interactions. The presentation traces the evolution from early analog detector electronics to modern digital solutions, focusing on enhancements in noise reduction, signal processing, and data throughput. It also discusses the latest developments in DAQ systems, such as real-time data processing, high-speed data transfer, and integration with trigger systems. Furthermore, innovations in monitoring technologies, including automated calibration and performance diagnostics, are examined to ensure experimental reliability and accuracy. This review aims to illustrate how these technological advancements are enhancing reactor neutrino experiments and facilitating future discoveries.

Speaker: Dr Ilham El Atmani (Hassan II University of Casablanca, Faculty of Science Ain Chock, High Energy Physics & Condensed Matter Laboratory (PHEMAC))

66 Extracting high performance of X-ray energy information in photon-counting computed tomography

X-ray computed tomography (CT) based on GOS scintillator coupled with photodiode is widely used in medical imaging. However, high image quality in conventional CT requires a high radiation dose, which leads to an inability to acquire energy information of X-rays. Therefore, as the next generation CT, the photon-counting CT (PCCT) has been proposed, which provides multi-energy and low-radiation-dose imaging. In PCCT, CT images in different energy bands can be subtracted to extract specific materials, a process known as “K-edge-imaging”. However, whether the obtained PCCT images corresponds to individual energy bands, as expected, has not been clearly investigated. Some previous studies have suggested that the energy information in PCCT, specifically low-energy information, may be substantially inaccurate due to the contamination of escape or Compton scattered events. In this study, we investigated the accuracy of energy information in obtained PCCT images. The PCCT detector developed in our system consisted of a multi-pixel photon counter coupled with a fast ceramic YGAG:Ce scintillator, thus can be easily constructed, has a lower total cost and has high compatibility with conventional CT systems. By imaging various phantoms, we confirmed that the experimental CT values in the low-energy bands is actually deviated from the theoretical values. Based on these results, we developed a novel correction method to reduce the effects of energy-miscounted X-ray photons by using the Geant4 simulation. As a result, the contrast of the CT images and CT values in the low-energy bands improved by approximately 35% after applying the correction. This correction method is independent of the phantom properties, which means that it can be applied in various imaging cases. We conclude that the proposed method can be effective at improving the accuracy of low-energy information in PCCT, which expands the application of PCCT energy information for clinical uses.

Speaker: Ryotaro MINAGAWA (Waseda University)

Lunch Break

New materials and Technologies

67 Pushing the limit of photodetction by bandage engineering through alloying and stacking

In this talk, we discuss harnessing the unique properties of amorphous selenium (a-Se) and its alloy. Our exploration into Te alloying has revealed critical insights into defect states and their impact on electronic properties. By integrating density functional theory (DFT) simulations with experimental validation, we discovered that while Te incorporation reduces the band gap and mobility, the quantum efficiencies can be recovered at higher electric fields due to enhanced carrier escape from trap states. Furthermore, we demonstrated the viability of multilayer detector architectures, leveraging the combined strengths of a-Se and Se-Te to achieve superior sensitivity across a broad spectral range, particularly in the UV to red wavelengths.

Speaker: Shiva Abbaszadeh (University of California, Santa Cruz)

68 Development of UV-Sensitive GaN Single Photon Geiger-Mode Avalanche Photodiodes

Silicon photomultipliers (SiPMs) have had a transformational impact on many important experiments in high-energy and astrophysics. However, the SiPM is intrinsically limited in its photoresponse below ~300 nm, a critical wavelength range for liquid noble scintillation detectors. An alternative to silicon for the fabrication of UV avalanche photodiodes (APDs) are the wide-bandgap III-N semiconductors AlGaN and GaN, which have a tunable direct bandgap energy and better sensitivity in the UV than Si detectors. With the commercial availability of high-quality native III-N substrates, we have successfully fabricated single GaN APDs and demonstrated enhanced UV sensitivity and Geiger-mode operation. Encouraged by these results, we improved our device design to reduce tunneling currents and device mesa edge breakdown, which we believe are the most significant contributors to the dark count rate near avalanche. We present measurements of our latest III-N APD devices with beveled mesas and a modified internal structure that lowered the dark current density 30,000 times.

Speaker: Dr Theeradetch Detchprohm (Georgia Institute of Technology)

69 UV hybrid photon detector based on GaN photocathodes and Si low gain avalanche diode

Photon detectors featuring single-photon sensitivity play a crucial role in various scientific domains, including high-energy physics, astronomy, and quantum optics. Fast response time, high quantum efficiency, and minimal dark counts are the characteristics that render them ideal candidates for detecting individual photons with exceptional signal-to-noise ratios, at frequencies in the range of hundreds of MHz. Here, we report on our first design and operational results on a Hybrid Photon Detector (HPD) that combines the high quantum efficiency of a Gallium Nitride (GaN) photocathode and the low noise characteristics of a Si-based Low-Gain Avalanche Diode (LGAD). This hybrid detection scheme has the potential to reach single-photon detection sensitivity with high quantum efficiency, low noise levels and capable of operating at hundreds of MHz repetition rates.

Speaker: Mohamed Boukhicha (Brookhaven National Laboratory)

70 Effects of Alpha and Gamma radiations on sensitivity of Zincoxide (ZnO) thin films synthesized on silicon substrate by solgel method

In this work we investigate the ability/sensitivity of Zinc Oxide under alpha and gamma radiations of approximately low energy and to check whether ZnO based photodetector (silicon substrate) is radiation hostile or not. Presently,there are different types of material including Silicon, Gallium Arsenide(GaAs) and Gallium Indium Phosphide (GaInP) etc are used as photon sensors that are radiation hard up to a certain threshold.
The manufacturing/synthesizing process,cost and increasing dark count rate with radiations left space to be filled by suitable candidate for the same purpose. The X-ray diffraction(XRD) measurements revealed that the crystalline phase of ZnO thin films does not change after irradiation and showed a hexagonal structure of wurtzite type with an orientation toward(002)[1]. Therefore, we focused only the sensitivity, response
and recovery time testing. An other main reason to check these parameters, is that we are searching an alternate sensing material which can replace the Si,GaAs and GaInP based photomultipliers to work inside the high radiation environment for detecting Cherenkov light in UA9 experiment at CERN[2]. Luckily, ZnO based photodetector has not shown any major changes or damages to the gamma(~1 MeV) and alpha radiations of ~5MeV which loses almost 99.9% energy inside the compound as per SRIM calculation (for almost 15 hrs).

Speaker: Dr Zahoor ul Islam (Gran Sasso Science Institute/ Federico II University of Naples Italy)

71 Scintillation Light Detection in Polycrystalline Diamond Using Single Photon Detectors

Single-crystal diamonds are used in particle detection via charge collection mode, benefiting from their high charge mobility and long carrier lifetime. However, their production is challenging and size-limited. Polycrystalline diamond, which can be produced more easily and in larger sizes through Chemical Vapor Deposition, offer a viable alternative as scintillators for charged particle detection. We present preliminary results on the scintillation properties of polycrystalline diamonds irradiated by alpha particles, including the scintillation time profile, light yield estimates, and imaging capabilities. The signals are detected using Silicon Photomultipliers (SiPMs), facilitating the development of compact, scalable detectors with imaging capabilities. Additionally, we will discuss potential applications, including a detector design for thermal neutrons utilizing SiPMs.

Speaker: Niccolo' Gallice (Brookhaven National Laboratory (US))

Coffee Break

MCP/PMT

72 The Detectors based on the PMTs

Photomultiplier tubes (PMTs) are general components in particle physics and nuclear physics experiments. They convert light signals into electrical signals. When a primary photoelectron comes from the photocathode of the PMT, it will be amplified by the dynode or MCPs. Especially in the neutrino observatory experiments and large cosmic ray experiments, where hundreds or even thousands of PMTs are employed to detect scintillator photons or water Cherenkov light. According to different experimental designs, different types of PMTs varying in either dimension or performance are selected. This talk will discuss different types of PMTs, and the detectors based on these types of PMTs.

Speaker: Sen Qian qians

73 Study of After-pulse of Fast Timing MCP-PMT and Its Performance in Magnetic Fields

The Microchannel Plate Photomultiplier (MCP-PMT), also known as Fast-timing PMT (FPMT), is a photosensitive device renowned for its high gain, exceptional detection efficiency, single-photon detection capability, magnetic field resistance, and superior time resolution. Widely utilized in high-energy physics and medical detection applications, the FPMT requires rapid time resolution and robust magnetic field resistance.

Of particular concern are after-pulses, undesired pulses occurring in a PMT following the initial pulse, which can compromise applications requiring minimal noise levels. To enhance the time performance of FPMTs, a comprehensive study was undertaken to investigate the after-pulse characteristics and origins across different FPMT models, encompassing both single-anode and 8 × 8 anode configurations.

Furthermore, to assess the viability of FPMT operation in high magnetic fields, a detailed examination was conducted to evaluate the impact of magnetic fields on the performance metrics of single-anode FPMTs and 8 × 8 anode FPMTs, including Rise Time (RT), Fall Time (FT), Transit Time Spread (TTS), gain, and amplitude.

Initial findings suggest that FPMTs exhibit robust single-photon detection capabilities at 2.4T when the magnetic field aligns parallel to the detector axis, with retained sensitivity at 1.2T even when the field is perpendicular. Notably, the 8 × 8 anode FPMTs display heightened susceptibility to magnetic fields compared to their single-anode counterparts. Further analysis of FPMT signals holds promise in elucidating the differential impact of magnetic fields on various FPMT models, thereby advancing their magnetic field resilience capabilities.

Speaker: Lingyue Chen

74 R&D of MCP-PMTs

Due to its superior temporal resolution, low dark noise and stability in magnetic fields, the microchannel plate photomultiplier tube (MCP-PMT) is an essential component of particle identification detectors such as LHCb, Belle II and STCF, as well as fast neutron or X-ray detectors in nuclear inertial confinement fusion (ICF) experiments. However, future work is needed to develop the MCP-PMT with a high rate capability, long lifetime, low after pulse and high spatial resolution. We have carefully studied the time characteristics, dynamic range, lifetime and magnetic field effects of the MCP-PMT through simulations and tests. Tracking the movement of electrons inside the MCP-PMT using 3D simulations is useful for understanding the behaviour and designing better versions. Several types of prototypes have been developed, including gated MCP-PMTs, multi-anode MCP-PMTs and high dynamic range MCP-PMTs. In the double cone ignition (DCI) laser fusion experiment conducted in China, more than 20 gated MCP-PMTs with a gating response time of 5 ns and a gating noise amplitude of ±2 mV were used. These MCP-PMTs successfully detected the fast neutron signals in the presence of a strong gamma-ray background. The lifetime of the multi-anode MCP-PMT developed for the super tam charm facility (STCF) is over 11C2/cm and the test is ongoing. The MCP-PMT with a linear anode output of 250 mA @ 100 ns is suitable for the detection of high levels of radiation.

Speaker: Prof. Ping Chen (XIOPM-CAS)

75 Characterization of the Hyper-Kamiokande 50-cm Photomultiplier Tubes

The Hyper-Kamiokande (HK), which is scheduled to start operation in 2027, is a gigantic water Cherenkov detector designed to observe a wide range of physics phenomena including neutrino oscillations and proton decay. Currently, the mass production of 50 cm diameter photomultiplier tubes (PMTs) for HK is in progress. A series of measurements are being conducted to evaluate the performance characteristics, identify variations, and ensure the long-term stability of the PMTs. Dark count rates, gain, timing resolution, after pulse, etc. are evaluated by processing signals generated at several kHz per PMT. An overview of these measurements and the resulting performance data of the PMTs will be reported.

Speaker: Sanshiro Goto

Closing Session

Friday 22 November

Visit to TRIUMF Laboratory