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Progress on the ALETHEIA project and a new approach to mitigate events overlap

Junhui Liao

TL;DR

The paper addresses detecting low-mass dark matter with liquid helium in a time projection chamber and the unique internal overlap caused by the long-lived triplet scintillation $S_{13}$ with lifetime $13~\text{s}$. It reports progress toward a single-phase LHe TPC, including a $4~\text{K}$-capable detector, TPB coating, and photosensors suitable for near-LHe temperatures, with measured electron escape fractions of about $10\%$ at $E_d=10~\text{kV/cm}$ and $25\%$ at $E_d=50~\text{kV/cm}$, consistent with COMSOL simulations. It proposes an event-discrimination algorithm that uses a $±1$ ms window to group S1/S1'/S2 as Part 1 and treats isolated signals as $S_{13}$, effective up to background rates from $1$ to $40~\text{Hz}$ given the drift times in the ms-to-s range. Cooling to $1$ K dramatically increases electron mobility (up to $10^3$) relative to $4$ K, shrinking drift times to the millisecond scale and enabling practical operation, with future work toward dual-phase LHe TPC development and broader implications for low-mass DM searches. Overall, the results support the viability of LHe-based detectors for low-mass DM and lay groundwork for next-generation experiments.

Abstract

The ALETHEIA project aims to search for low-mass dark matter using liquid helium (LHe)-filled time projection chambers (TPCs). While liquid argon and liquid xenon TPCs have been extensively employed in the field of direct dark matter detection, successful development of LHe TPCs has not yet been achieved. Launched in 2020, our project has made significant progress since then. These advancements have convinced us that a single-phase LHe TPC is technologically feasible. Compared to liquid xenon and liquid argon TPCs, one of the unique challenges for LHe TPCs is event overlap caused by the 13-second lifetime scintillation. We will demonstrate that this overlap can be entirely mitigated when the LHe temperature is maintained near 1.0 K. At this temperature, electron mobility is three orders of magnitude higher than at approximately 4.0 K, which is the temperature we initially proposed for the LHe TPC.

Progress on the ALETHEIA project and a new approach to mitigate events overlap

TL;DR

The paper addresses detecting low-mass dark matter with liquid helium in a time projection chamber and the unique internal overlap caused by the long-lived triplet scintillation with lifetime . It reports progress toward a single-phase LHe TPC, including a -capable detector, TPB coating, and photosensors suitable for near-LHe temperatures, with measured electron escape fractions of about at and at , consistent with COMSOL simulations. It proposes an event-discrimination algorithm that uses a ms window to group S1/S1'/S2 as Part 1 and treats isolated signals as , effective up to background rates from to given the drift times in the ms-to-s range. Cooling to K dramatically increases electron mobility (up to ) relative to K, shrinking drift times to the millisecond scale and enabling practical operation, with future work toward dual-phase LHe TPC development and broader implications for low-mass DM searches. Overall, the results support the viability of LHe-based detectors for low-mass DM and lay groundwork for next-generation experiments.

Abstract

The ALETHEIA project aims to search for low-mass dark matter using liquid helium (LHe)-filled time projection chambers (TPCs). While liquid argon and liquid xenon TPCs have been extensively employed in the field of direct dark matter detection, successful development of LHe TPCs has not yet been achieved. Launched in 2020, our project has made significant progress since then. These advancements have convinced us that a single-phase LHe TPC is technologically feasible. Compared to liquid xenon and liquid argon TPCs, one of the unique challenges for LHe TPCs is event overlap caused by the 13-second lifetime scintillation. We will demonstrate that this overlap can be entirely mitigated when the LHe temperature is maintained near 1.0 K. At this temperature, electron mobility is three orders of magnitude higher than at approximately 4.0 K, which is the temperature we initially proposed for the LHe TPC.

Paper Structure

This paper contains 5 sections, 1 figure.

Table of Contents

  1. ALETHEIA introduction
  2. The progress of ALETHEIA so far
  3. Mitigating the possible events overlap due to the 13 s lifetime scintillation
  4. Summary
  5. Acknowledgement

Figures (1)

  • Figure 1: An example of event overlap arising from the 13 s scintillation lifetime is shown, along with its significant mitigation in a 1 K LHe TPC under the assumption of a 1 Hz background event rate.