Performance Optimization and Characterization of 7-pad Resistive PICOSEC Micromegas Detectors

TL;DR

This work investigates resistive-layer implementations in PICOSEC Micromegas detectors to enhance robustness for precision timing in high-rate environments. By comparing seven-pad prototypes with uniform and capacitive-sharing resistive architectures, tested under identical drift-gap and field conditions at CERN, the study identifies the ten-megaohm-per-square configuration as the optimal compromise, delivering ~22.9 ps timing and ~1.19 mm spatial resolution while enabling effective charge sharing. The analysis demonstrates that multi-pad timing can be combined without external tracking, achieving sub-28 ps resolution in shared regions and mapping spatial performance across the full detector, with ~1.19 mm spatial precision and uniform timing within ~35 ps across the active area. The results establish a practical foundation for scalable resistive MPGD timing detectors (e.g., ENUBET), highlighting the importance of mechanical planarity and accurate photocathode alignment for uniform response and guiding the design of future multi-pad systems.

Abstract

We present a comprehensive characterization of resistive PICOSEC Micromegas detector prototypes, tested under identical conditions, constant drift gap, field configurations, and photocathode at the CERN SPS H4 beam line. This work provides a proof of concept for the use of resistive layer technology in gaseous timing detectors, demonstrating that robustness can be improved without compromising the excellent timing performance of PICOSEC Micromegas. Different resistive architectures and values were explored to optimize stability and ensure reliable long-term operation in challenging experimental environments. The prototype with a 10MΩ resistive layer achieved the best overall performance, with a timing resolution of 22.900 {\pm} 0.002 ps and a spatial resolution of 1.190 {\pm} 0.003 mm, while charge sharing across multiple pads enabled combined timing resolutions below 28 ps. A lower-resistivity (200kΩ) configuration exhibited enhanced charge spread, leading to minor systematic offsets in reconstructed pad centers, yet maintained robust timing and spatial performance. Capacitive charge-sharing architectures improved spatial resolution in some regions but suffered from signal attenuation and nonuniform charge distributions, resulting in slightly degraded timing (33.300 {\pm} 0.002 ps) and complex localization patterns. Mechanical precision, particularly readout planarity and photocathode alignment, was identified as critical for uniform detector response. These studies benchmark the potential of resistive layers for gaseous timing detectors and provide a foundation for scalable designs with optimized timing and spatial resolution across diverse experimental applications.

Figures (18)

• Figure 1: (a) Graphical representation of a PICOSEC Micromegas detector BORTFELDT2018317. (b) Typical PICOSEC Micromegas signal after the amplifier.
• Figure 2: Schematic description of the resistive PICOSEC Micromegas detector layout Janssens:2890572.
• Figure 3: Left: Full detector assembly on the chamber. Right(from top to bottom): Step-by-step the assembly procedure, from the readout PCB, the drift copper ring, which preserves electrical contact and defines the drift gap size, the 5 cm crystal placement on top of the drift spacer, and the peak support.
• Figure 4: Block diagram and sketch of the electronic modules used to provide NIM signal to trigger the DAQ.
• Figure 5: Top:2D distribution of the beam profile that illuminates the area around the instrumented PICOSEC-Micromegas detector. Bottom: (Left) Track hits, representing the number of entries in each 2D bin. (Right) 2D track distribution weighted by pad-0 charge.