Design and Performance of a 96-channel Resistive Micromegas Detector for ENUBET

TL;DR

This work advances large-area, picosecond-timing gaseous detectors by presenting a 96-pad resistive PICOSEC-Micromegas prototype optimized for ENUBET. The design integrates a 2.5 nm Diamond-Like Carbon photocathode with a 10 MΩ/□ resistive Micromegas, a precision drift gap defined by spacers, and a modular readout suitable for tiling into larger matrices. Beam tests with 150 GeV muons achieve a per-pad timing around 43 ps in the central region and demonstrate uniform Signal Arrival Time distributions across the tested area, with planarity control to about 10 μm identified as critical for uniform response. The results establish a scalable path toward large-area, picosecond-level gaseous timing detectors for monitored neutrino beam experiments like ENUBET, with future work focusing on full-channel readout, long-term stability, and system integration.

Abstract

The PICOSEC-Micromegas (PICOSEC-MM) detector is a fast gaseous detector that achieves picosecond-level timing by coupling a Cherenkov radiator, typically an MgF2 crystal, to a Micromegas-based photodetector with a photocathode. This configuration allows the fast photoelectron-induced signal to suppress the intrinsic time jitter of gaseous detectors, enabling sub-20 ps timing precision while preserving the robustness and scalability of micro-pattern gaseous detector technologies. The 96-pad PICOSEC-MM detector is a large-area demonstrator optimized for precision timing in high-energy physics, building on research and development insights from earlier 7-pad resistive prototypes to validate scalability, uniformity, and robustness for the ENUBET project. It employs a 2.5 nm diamond-like carbon photocathode and a Micromegas board with a surface resistivity of 10 megaohms per square, and was characterized using 150 GeV/c muons at the CERN SPS beamline, with one-third of the active area instrumented per run. A dedicated alignment procedure for multi-pad PICOSEC-MM systems was used to reconstruct pad centers and merge measurements across regions, yielding a timing resolution of 43 ps and uniform signal arrival time distributions over the tested area. Mechanical flatness was identified as a key factor, with planarity tolerances within 10 micrometers required to maintain good timing resolution, and the successful operation of the 96-pad demonstrator confirms the scalability of the PICOSEC-MM concept toward robust, high-granularity, picosecond-level gaseous timing detectors for monitored neutrino beam experiments such as ENUBET.

Figures (13)

• Figure 1: (a) Graphical representation of a PICOSEC Micromegas detector test. (b) Typical PICOSEC Micromegas signal after the amplifier.
• Figure 2: Schematic of the muon stations and absorbers configuration to be installed at the end of the tagger calorimeter. The grey slabs represent the absorbers (made out of iron or rock) while the white slices, 8 in total, are the muon detector planes Longhin:2714046.
• Figure 3: Left: Readout plane of the 96-pad detector design. Middle: Resistive DLC layer deposited on top of the readout pads. Right: Positioning of the drift spacers on the PCB plane.
• Figure 4: Signal routing configuration for the 96-pad board. Two internal copper layers were used to balance signal length and minimize crosstalk.
• Figure 5: Exploded view of the 10$\times$10 pad detector assembly. From left to right: 3D-printed entrance window for single-photoelectron calibration, 3 mm-thick quartz entrance window with its support and flange ensuring gas tightness and vacuum compatibility, front aluminum window of the entry chamber, spacer defining the drift gap and HV on the radiator, radiator, O-ring for gas tightness, bulk-Micromegas PCB, rear O-ring and aluminum backplate, and finally the metallic support used to mount the chamber on the test-beam telescope.