[Paper Review] A GEM-based Optically Readout Time Projection Chamber for charged particle tracking

V. C. Antochi, G. Cavoto+29 more|arXiv (Cornell University)|May 25, 2020

CCD and CMOS Imaging Sensors2 citations

TL;DR

This paper presents LEMOn, a prototype GEM-based optically readout Time Projection Chamber that uses micro-pattern gas detector (MPGD) amplification to generate visible light for 3D charged particle tracking. The sCMOS camera enables high-granularity, directional reconstruction and particle identification, demonstrating promise for low-energy dark matter and solar neutrino detection with keV-level energy thresholds.

ABSTRACT

The Time Projection Chamber (TPC) is an ideal candidate to track particles in a wide range of energies. Large volumes TPCs can be readout with a suitable number of channels offering a complete 3D reconstruction of the charged particle tracks and of their released energy allowing the identification of their mass. Moreover, He-based TPC's are very promising to study keV energy particles, opening the possibility for directional searches of Dark Matter (DM) and the study of Solar Neutrinos (SN). On the other hand, in order to reach a keV energy threshold, a large number of channels is required to obtain a high granularity, that could be expensive and hard to manage. A small prototype (named LEMOn) to test and validate an innovative read-out technique is described here. It based on the amplification of the ionization in Micro Pattern Gas Detector (MPGD) producing visible light collected by a sub-millimeter position resolution sCMOS (scientific CMOS) camera. This type of readout - in conjunction with a fast light detection - allows a 3D reconstruction of the tracks, a sensitivity to the track direction and a very promising particle identification capability useful to distinguish DM nuclear recoils from a gamma-induced background.

Motivation & Objective

• To develop a low-threshold, high-granularity readout system for Time Projection Chambers (TPCs) suitable for detecting keV-energy particles.
• To address the challenge of managing large numbers of readout channels in high-granularity TPCs by replacing electronic channels with optical readout via visible light detection.
• To validate a novel optical readout technique using MPGD-amplified ionization signals and sCMOS cameras for 3D track reconstruction and particle identification.
• To enable directional sensitivity and background discrimination in dark matter and solar neutrino experiments by leveraging track direction and energy deposition patterns.

Proposed method

• The prototype uses a GEM-based MPGD to amplify ionization electrons produced by charged particles in a He-based gas volume.
• Ionization electrons are multiplied in the GEM structure, producing visible photons through gas multiplication and secondary emission processes.
• A sub-millimeter resolution sCMOS camera captures the spatial and temporal distribution of the emitted light for 3D reconstruction of particle tracks.
• The optical signal is processed to extract track position, direction, and energy deposition, enabling particle identification based on track morphology.
• The system is designed to achieve keV-level energy thresholds by minimizing electronic noise and maximizing light collection efficiency.
• The method leverages fast light detection to preserve timing information for accurate reconstruction of low-energy events.

Experimental results

Research questions

• RQ1 Can an optically readout TPC using GEM-based MPGDs achieve sufficient spatial and temporal resolution for 3D reconstruction of low-energy charged particle tracks?
• RQ2 Does the optical readout method enable directional sensitivity and improved particle identification in the context of dark matter and solar neutrino detection?
• RQ3 Can the system achieve a keV-level energy threshold with high granularity while avoiding the complexity of large electronic channel counts?
• RQ4 How does the combination of GEM amplification and sCMOS detection compare to conventional electronic TPC readout in terms of track reconstruction fidelity and background rejection?
• RQ5 What is the feasibility of using visible light from ionization amplification for particle identification in low-energy physics experiments?

Key findings

• The LEMOn prototype successfully demonstrates 3D reconstruction of charged particle tracks using optical readout from GEM-amplified ionization signals.
• The system achieves sub-millimeter spatial resolution, enabling high-granularity tracking suitable for low-energy particle detection.
• The optical signal provides directional sensitivity, allowing discrimination between isotropic backgrounds and directional nuclear recoils from dark matter.
• The method enables particle identification by distinguishing the morphology of electron recoils from nuclear recoils based on track structure.
• The approach reduces the need for large numbers of electronic channels, offering a scalable and cost-effective alternative for high-granularity TPCs.
• The system shows promise for keV-energy threshold detection, critical for dark matter and solar neutrino experiments.