Design and performance of a 96-channel resistive PICOSEC Micromegas detector for ENUBET

Abstract The PICOSEC-Micromegas (PICOSEC-MM) detector is a fast gaseous detector concept that achieves picosecond-level timing. It couples a Cherenkov radiator, typically an MgF 2 crystal, to a Micromegas-based photodetector equipped with a photocathode, allowing the fast photoelectron-induced signal to suppress the intrinsic time jitter characteristic of gaseous detectors. This design enables sub-20 ps timing precision while preserving the robustness and scalability of Micro-Pattern Gaseous Detector (MPGD) technologies. The 96-pad PICOSEC-MM detector represents the latest advancement in this development, optimized for precision timing in high-energy physics. Building upon the R&D insights obtained with earlier 7-pad resistive prototypes, this large-area demonstrator was developed to validate the scalability, uniformity, and robustness of the technology for integration into the ENUBET project. The detector employs a 2.5 nm Diamond-Like Carbon (DLC) photocathode with a Micromegas board equipped with surface resistivity of 10 MΩ/□, providing an excellent timing performance. The prototype was characterized using 150 GeV/ c muons at the CERN SPS beamline, with one-third of the active area instrumented during each run. A dedicated alignment procedure, developed for multi-pad PICOSEC-MM systems, was used to reconstruct the pad centers and combine measurements across different detector regions. The measured timing resolution was 43 ps across the instrumented pads, while the Signal Arrival Time (SAT) distributions exhibited a good uniformity among the detector area that was tested. Mechanical flatness was identified as a key factor influencing timing precision. Maintaining a planarity tolerance within 10 μm is therefore critical to preserve a good timing resolution over large active areas. The successful operation of the 96-pad demonstrator confirms the scalability of the PICOSEC-MM concept marking a significant step toward implementing robust, high-granularity, picosecond-level gaseous timing detectors in monitored neutrino beam experiments such as ENUBET.