Développement d'un détecteur PICOSEC-Micromegas pour ENUBET – PIMENT
Development of a PICOSEC Micromegas detector for ENUBET (PIMENT)
Towards large-area picosecond timing instrumentation for monitored neutrino beams
Scientific and technological challenges and objectives
The PIMENT project addresses major scientific and technological challenges related to the development of fast-timing detector instrumentation for particle physics experiments. Precise time measurements at the level of a few tens of picoseconds have become essential to cope with high particle rates, reduce pile-up effects, and enable event-by-event correlations. Achieving such performance over large detector surfaces remains a key challenge when constraints on channel density, cost, robustness, and long-term operation are taken into account. Solid-state timing detectors provide excellent intrinsic time resolution but rely on very fine segmentation, leading to extremely high numbers of readout channels when large areas must be instrumented. In contrast, gaseous detectors naturally offer large-area coverage, robustness, and radiation tolerance, but have traditionally been limited by timing fluctuations associated with direct gas ionization. The PICOSEC-Micromegas concept, developed prior to this project, demonstrated that this limitation can be overcome by replacing direct gas ionization with prompt photoelectrons produced by Cherenkov light in a radiator coupled to a photocathode. While this established the feasibility of picosecond timing with gaseous detectors, applicability to realistic, large-scale systems remained an open challenge. The main scientific enjeu of PIMENT is to bridge the gap between proof-of-principle demonstrations and deployable detector technology. This requires extending optimized single-channel performance to large-area, multi-channel detectors with centimetre-scale pixels, while preserving timing resolution at or below 50 ps. Achieving this involves controlling detector planarity at the micrometre scale, ensuring uniform electric fields, mitigating discharge effects, and maintaining stable operation under high particle fluxes. Another objective is to develop photocathode solutions compatible with long-term operation. While CsI photocathodes provide high photoelectron yield, their sensitivity to humidity, ageing, and ion backflow limits use in high-rate environments. The project therefore aims to qualify more robust alternatives, such as carbon-based or metallic photocathodes, combining sufficient photoelectron yield with improved stability. A further objective is the development of dedicated fast front-end and back-end electronics capable of multi-channel readout with picosecond-level precision, preserving intrinsic detector performance and remaining scalable to large channel counts. Finally, PIMENT aims to demonstrate the relevance of PICOSEC-Micromegas detectors for precision neutrino beam instrumentation within the ENUBET framework, where fast timing enables time and flavour tagging and reduces systematic uncertainties.
The PIMENT project adopted an integrated and iterative methodological approach combining detector design, materials research, electronics development, simulation, and experimental validation. The overall strategy was to progressively evolve the PICOSEC-Micromegas concept from optimized single-channel prototypes to large-area, multi-channel detector systems compatible with realistic experimental conditions.
The work began with detailed studies on small-area PICOSEC-Micromegas detectors to optimize the fundamental parameters governing timing performance. This included systematic variations of the drift gap thickness, electric field configuration, gas composition, and operating voltages. These studies were supported by dedicated laboratory setups using femtosecond UV lasers and reference timing detectors, enabling precise characterization of signal formation and timing fluctuations.
Building on these results, the methodology evolved towards the design and fabrication of large-area, pixelated detectors with pad sizes of 1 cm². Particular emphasis was placed on mechanical design and assembly procedures to achieve detector planarity at the micrometre level, a critical requirement for uniform timing performance. Resistive anode technologies were implemented to ensure stable operation at high rates and to mitigate discharge effects, while preserving fast signal response.
Photocathode R&D followed a parallel and complementary approach. In addition to the reference CsI photocathodes, alternative materials such as boron carbide, diamond-like carbon, and metallic layers were developed and characterized. Optical modelling was combined with quantum efficiency measurements, ageing studies, and beam tests to assess performance, robustness, and long-term stability. These studies guided the selection of photocathode solutions compatible with high-rate operation.
Electronics development was closely coupled to detector R&D. Dedicated fast front-end and back-end electronics were developed to support multi-channel readout while preserving picosecond-level timing. The readout architecture relied on waveform digitization, allowing detailed signal reconstruction and advanced timing extraction methods. Despite significant delays caused by global supply-chain disruptions, the electronics architecture was adapted and successfully scaled to larger channel counts.
Simulation and system-level studies complemented the experimental work. Detector simulations were used to understand timing mechanisms and guide design choices, while physics-driven simulations within the ENUBET framework defined performance requirements and integration scenarios. Throughout the project, laboratory measurements and particle beam tests were used to validate each development stage, ensuring a continuous feedback loop between design, simulation, and experimental results.
The PIMENT project achieved all its core scientific and technical goals and produced results that significantly advanced the maturity of the PICOSEC-Micromegas fast-timing detector concept, from laboratory optimization to system-level validation.
A first major result concerns the successful extension of the PICOSEC-Micromegas concept from single-channel prototypes to large-area, multi-channel detectors. Pixelated detectors with an active area of 10×10 cm² and up to 96 readout pads of 1 cm² were designed, fabricated, and characterized. Mechanical planarity better than 10 µm was achieved, leading to homogeneous electric fields and uniform detector response. Measurements demonstrated gain and timing uniformity across the detector surface at the level of about 10%, validating the scalability of the concept to large areas with a limited number of electronic channels.
In terms of timing performance, state-of-the-art results were obtained. Small-area prototypes equipped with optimized CsI photocathodes achieved time resolutions in the range of 13–18 ps for minimum ionizing particles, corresponding to photoelectron yields of approximately 10–11 p.e./MIP. Large-area detectors using robust photocathodes such as boron carbide (B₄C) or diamond-like carbon (DLC) achieved time resolutions around 40 ps for 150 GeV muons, demonstrating that sub-50 ps timing can be preserved in realistic, multi-channel configurations.
Significant progress was achieved in photocathode development. Systematic studies of CsI, carbon-based, and metallic photocathodes were carried out using monochromators, laser setups, ageing tests, and particle beams. Robust photocathodes yielding 3–4 p.e./MIP were validated, enabling stable operation at high particle rates while maintaining competitive timing performance. Optical modelling guided the optimization of radiator thickness and substrate materials.
Dedicated fast front-end and back-end electronics were successfully developed and integrated. A scalable readout system based on waveform digitization was implemented, supporting up to 256 channels with sampling rates exceeding 6 GS/s. Despite delays caused by global microelectronics supply-chain disruptions, the electronics were fully operational and enabled advanced signal processing and precise timing reconstruction.
A major outcome of PIMENT, going beyond the initial project deliverables, was the production of a complete PICOSEC-Micromegas demonstrator developed for the ENUBET programme. Three fully equipped detectors were assembled and tested during a system-level beam campaign at the CERN PS in October 2025. These tests validated stable operation under realistic beam conditions and confirmed the detector performance in an environment representative of a monitored neutrino beam.
The results obtained within the PIMENT project open clear perspectives for both the consolidation of the PICOSEC-Micromegas technology and its application to future particle physics experiments requiring precise timing over large detector surfaces. By demonstrating that sub-50 ps timing resolution can be achieved in scalable, multi-channel gaseous detectors with centimetre-scale pixels, PIMENT has established a solid technological baseline for further developments.
A first perspective concerns the extension of the detector concept to larger active areas. Future work will focus on scaling beyond the 10×10 cm² prototypes through optimized tiling strategies, improved mechanical designs, and reinforced control of long-term planarity and stability. Continued efforts on photocathode optimization, in particular using carbon-based or metallic materials and protective layers, are expected to further improve photoelectron yield and lifetime while maintaining robustness in high-rate environments.
At the system level, the successful development and beam testing of a PICOSEC-Micromegas demonstrator for the ENUBET programme represent a key step towards deployment in next-generation tagged neutrino beam facilities. The demonstrated performance has supported the evolution of ENUBET towards the nuScope concept, where fast timing plays a central role in neutrino beam monitoring. In this context, PICOSEC-Micromegas detectors are now considered not only for the instrumentation of the hadron dump but also for the muon spectrometer, where precise timing over large acceptance is essential for muon tagging and improved control of the neutrino flux from pion decays.
Beyond neutrino physics, the characteristics of PICOSEC-Micromegas detectors make them attractive for other large-scale experiments. In particular, the technology is being examined for external timing layers in future collider projects such as the Future Circular Collider (FCC), where pile-up mitigation and event association require precise timing over extended areas, combined with moderate channel density and robust operation.
From a methodological perspective, future developments will also benefit from advanced signal processing and reconstruction techniques, including refined waveform analysis and machine-learning-based timing extraction, building on the electronics and data acquired within PIMENT. Finally, the results and demonstrators produced by PIMENT provide a strong foundation for follow-up projects and coordinated R&D efforts, supporting the long-term adoption of large-area picosecond-timing gaseous detectors in precision particle physics experiments.
Le projet ENUBET (Enhanced NeUtrino BEams from kaon Tagging) vise à construire un faisceau de neutrinos monitoré afin de réduire l'incertitude sur le flux et la section efficace des neutrinos à <1%. Face au taux élevé d'événements attendus dans ENUBET, la résolution temporelle du détecteur est essentielle pour la reconstruction et la diminution de l’empilement d’événements. Un échantillonnage des détecteurs sub-ns permettrait une corrélation un à un entre les positrons tagués dans la ligne de faisceau et les neutrinos tagués dans le détecteur lointain, transformant ENUBET en premier "faisceau de neutrinos tagués". Nous proposons un projet de R&D de 3 ans pour développer des nouveaux instruments de détection basés sur le concept PICOSEC-Micromegas et démontrer l'impact de ces détecteurs sur les recherches de Nouvelle Physique. L'exploitation éventuelle de la technologie PICOSEC-Micromegas sera étudiée pour le tagueur et les détecteurs de neutrinos de ENUBET.Cela concerne :
- un détecteur PICOSEC Micromegas intégré dans un calorimètre électromagnétique, avec précision temporelle(~10 ps)
- un détecteur PICOSEC Micromegas remplaçant le veto des photons sur ENUBET, servant comme une couche de timing (T0-layer) dans le tagger pour la détection des MIPs (<50ps)
- instrumentation de l'arrêt du faisceau (beam dump) pour monitorer les muons
- Photodétecteur Micromegas pour le tagging temporel dans le détecteur de neutrinos.
Le concept PICOSEC-Micromegas consiste en un détecteur Micromegas "à deux étages" couplé à un radiateur Cherenkov (MgF2), équipé d'une photocathode appropriée. Le gap de dérive est réduit à 200 µm tandis que le champ électrique appliqué dans cette région (>10 kV/cm) est suffisamment fort pour produire une multiplication des électrons. Cette configuration offre une large bande pour la production et la détection de la lumière Cherenkov dans le VUV. Les particules relativistes traversant le radiateur produisent des photons Cherenkov qui sont simultanément convertis en électrons sur la photocathode. Les résultats obtenus avec de petits prototypes donnent une résolution temporelle de 24 ps pour les muons relativistes et de 44 ps pour les photons UV individuels. Ces résultats ont démontré que les performances temporelles souhaitées peuvent être atteintes avec ce concept. Cependant, il y a plusieurs questions à régler, principalement le passage à l'échelle pour des détecteurs de grande surface, y compris le développement de l'électronique correspondante, et des photocathodes efficaces et robustes pour des applications dans des environnements à flux de particules élevés.
Afin de démontrer dans des faisceaux de particules les performances requises, nous développerons des prototypes modulaires (~10x10 cm2).Les principaux défis techniques à surmonter sont le choix d'une photocathode efficace et robuste ainsi que la production de panneaux Micromegas avec anode segmentée et planarité meilleure que 10 µm, en conservant une petite longueur de rayonnement. En parallèle, nous développerons l'électronique nécessaire pour tester et évaluer les prototypes.Les cartes frontales seront développées sur la base de l'optimisation d'un amplificateur prototype existant, déjà testé avec succès sur un détecteur prototype. La numérisation des signaux et le marquage temporel précis seront effectués par des cartes électroniques basées sur le circuit SAMPIC.
L'importance de la précision temporelle dans les expériences opérant sur les faisceaux de particules à haute luminosité est déjà largement reconnue, tandis que la reconstruction 4D des objets sera nécessaire pour les expériences dans les accélérateurs futures. Ce projet vise à aborder les points critiques pour le développement d'un détecteur de dimension adéquate, capable d'offrir la précision temporelle nécessaire. Le projet met en valeur les avantages du PICOSEC Micromegas pour l’identification de particules, mais aussi comme un couche de timing intégré dans un calorimètre.
Coordination du projet
Thomas Papaevangelou (Institut de Recherche sur les lois Fondamentales de l'Univers)
L'auteur de ce résumé est le coordinateur du projet, qui est responsable du contenu de ce résumé. L'ANR décline par conséquent toute responsabilité quant à son contenu.
Partenariat
CENBG CENTRE D'ETUDES NUCLEAIRES DE BORDEAUX GRADIGNAN
IJCLab Laboratoire de physique des 2 infinis – Irène Joliot-Curie
LIST Laboratoire d'Intégration des Systèmes et des Technologies
IRFU Institut de Recherche sur les lois Fondamentales de l'Univers
Aide de l'ANR 574 089 euros
Début et durée du projet scientifique :
- 36 Mois
