μRWELL-PICOSEC: Precision Timing with Resistive Micro-Well Detector

TL;DR

μRWELL-PICOSEC investigates a resistive μRWELL-based MPGD coupled to a Cherenkov MgF$_2$ radiator with a thin photocathode to deliver precision timing in the tens of picoseconds. The work presents design, fabrication, and beam-tests of single-pad prototypes, examining hole geometries, readout patterns, and photocathode materials (CsI and DLC) using a CERN RD51 beam-line with an MCP-PMT reference for sub-25 ps timing. Key findings show a best timing of $23.5 \,\pm\,0.53$ ps for a CsI-coated proto, with CsI generally outperforming DLC due to higher QE; however, DLC offers robustness, motivating further material exploration. The results support the potential to reach sub-20 ps timing and scalable large-area detectors, with future R&D aimed at material robustness and applications such as FCC-ee muon timing.

Abstract

The PICOSEC detector concept uses a micro-pattern gaseous detector (MPGD) amplification structure combined with a Cerenkov radiator coated with a semi-transparent photocathode to provide below tens of picosecond-level precision timing capabilities with minimum ionizing particles. PICOSEC has triggered interest in the development of time-of-flight detectors for particle identification and timing detectors for track reconstruction in the high rate environment of future nuclear and high energy physics experiments. The PICOSEC Micromegas (or PICOSEC-MM) detector, developed by the CERN-based PICOSEC collaboration, use the Micromegas structure for gaseous amplification and achieve below 20 ps timing resolution. A new type of PICOSEC detector, the μRWELL-PICOSEC based on μRWELL amplification structure, is being investigated at Thomas Jefferson National Accelerator Facility (Jefferson Lab) alongside PICOSEC-MM R&D efforts in Europe. Preliminary results from the two 2024 beam test campaigns at CERN demonstrate a timing performance better than 24 ps is achievable with a single-channel μRWELL-PICOSEC prototype. A vigorous R&D effort is ongoing to improve the timing performance, robustness and operational stability of μRWELL-PICOSEC detectors. Development of a large size μRWELL-PICOSEC is also under consideration for applications in large scale experiments.

Figures (12)

• Figure 1: Cross section of a $\muup$RWELL-PICOSEC detector layout (not to scale).
• Figure 2: Top panel -- (a): Exploded 3D view of the single-channel $\muup$RWELL-PICOSEC prototype design; (b): Picture of the $\muup$RWELL PCB, a key component of the detector; (c): Front and rear view of the fully assembled prototype; Bottom panel -- (d): to (g): Assembly steps in sequential order of a single-pad $\muup$RWELL-PICOSEC detector; (h): The outer PCB closes and seals the aluminum housing and provides a HV supply to the pre-amplifier and a robust grounding scheme.
• Figure 3: (a): Layout and pictures of the $\muup$RWELL PCBs; (b): Cartoon of two $\muup$RWELL hole geometries, round holes (left) and square holes (right); (c): Cartoon of two readout pad geometries, plain Cu electrode (left) and hashed geometry Cu electrode to minimize detector capacitance (right); (d): Table summarizing the geometrical parameters of the $\muup$RWELL PCBs for different prototypes.
• Figure 4: $\muup$RWELL-PICOSEC telescope with three GEM trackers, a MCP-PMT detector for reference time and a stand for four single-pad $\muup$RWELL-PICOSEC prototypes. A schematic of the telescope layout is shown on the bottom left.
• Figure 5: (Left): Distributions of the signal amplitude for the MCP-PMT and one $\muup$RWELL-PICOSEC proto #5; (center) 2D mapping of the spatial distribution of the detector efficiency where the area inside the red circle represents the projection of the 4 mm diameter acceptance region of the MCP-PMT with minimal and uniform time resolution; (right) Distribution of the rise time of the $\muup$RWELL-PICOSEC proto #5.