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Design and characterization of a photosensor system for the RELICS experiment

Jijun Yang, Ruize Li, Chang Cai, Guocai Chen, Jiangyu Chen, Huayu Dai, Rundong Fang, Fei Gao, Jingfan Gu, Xiaoran Guo, Jiheng Guo, Gaojun Jin, Gaojun Ju, Yanzhou Hao, Yang Lei, Kaihang Li, Meng Li, Minhua Li, Shengchao Li, Siyin Li, Tao Li, Qing Lin, Jiajun Liu, Sheng Lv, Guang Luo, Kangwei Ni, Chuanping Shen, Mingzhuo Song, Lijun Tong, Jun Wang, Xiaoyu Wang, Wei Wang, Xiaoping Wang, Zihu Wang, Yuehuan Wei, Liming Weng, Xiang Xiao, Lingfeng Xie, Litao Yang, Long Yang, Jingqiang Ye, Jiachen Yu, Qian Yue, Yuyong Yue, Bingwei Zhang, Yuming Zhang, Yifei Zhao, Chenhui Zhu

TL;DR

This work addresses PMT saturation from surface muons in RELICS by implementing a dynamic readout base that combines anode and seventh-dynode signals to extend the PMT linear range. The authors validate the approach with bench tests, quantify saturation recovery via a two-parameter model, and demonstrate improved waveform fidelity for muon-induced S2 signals, enabling reliable CE$ u$NS measurements under cosmic backgrounds. Key contributions include extending linear response by nearly two orders of magnitude, characterizing recovery on $ ext{ms}$ timescales, and showing substantial muon-S2 signal preservation (up to $ ext{68 extpercent}$ with dynode-7, higher for deeper dynodes). The results have practical implications for RELICS and other LXe-based detectors, potentially enabling MeV-scale interactions to be probed with high sensitivity while maintaining accurate energy and timing information.

Abstract

In this paper, we present the design and characterization of a photosensor system developed for the RELICS experiment. A set of dynamic readout bases was designed to mitigate photomultiplier tube (PMT) saturation caused by intense cosmic muon backgrounds in the surface-level RELICS detector. The system employs dual readout from the anode and the seventh dynode to extend the PMT's linear response range. In particular, our characterization and measurements of Hamamatsu R8520-406 PMTs confirm stable operation under positive high-voltage bias, extending the linear response range by more than an order of magnitude. Furthermore, a model of PMT saturation and recovery was developed to evaluate the influence of cosmic muon signals in the RELICS detector. The results demonstrate the system's capability to detect coherent elastic neutrino-nucleus scattering (CE$ν$NS) signals under surface-level cosmic backgrounds, and suggest the potential to extend the scientific reach of RELICS to MeV-scale interactions.

Design and characterization of a photosensor system for the RELICS experiment

TL;DR

This work addresses PMT saturation from surface muons in RELICS by implementing a dynamic readout base that combines anode and seventh-dynode signals to extend the PMT linear range. The authors validate the approach with bench tests, quantify saturation recovery via a two-parameter model, and demonstrate improved waveform fidelity for muon-induced S2 signals, enabling reliable CENS measurements under cosmic backgrounds. Key contributions include extending linear response by nearly two orders of magnitude, characterizing recovery on timescales, and showing substantial muon-S2 signal preservation (up to with dynode-7, higher for deeper dynodes). The results have practical implications for RELICS and other LXe-based detectors, potentially enabling MeV-scale interactions to be probed with high sensitivity while maintaining accurate energy and timing information.

Abstract

In this paper, we present the design and characterization of a photosensor system developed for the RELICS experiment. A set of dynamic readout bases was designed to mitigate photomultiplier tube (PMT) saturation caused by intense cosmic muon backgrounds in the surface-level RELICS detector. The system employs dual readout from the anode and the seventh dynode to extend the PMT's linear response range. In particular, our characterization and measurements of Hamamatsu R8520-406 PMTs confirm stable operation under positive high-voltage bias, extending the linear response range by more than an order of magnitude. Furthermore, a model of PMT saturation and recovery was developed to evaluate the influence of cosmic muon signals in the RELICS detector. The results demonstrate the system's capability to detect coherent elastic neutrino-nucleus scattering (CENS) signals under surface-level cosmic backgrounds, and suggest the potential to extend the scientific reach of RELICS to MeV-scale interactions.

Paper Structure

This paper contains 12 sections, 6 equations, 11 figures.

Table of Contents

  1. Introduction
  2. Muon-induced backgrounds
  3. Design of dynamics readout base
  4. Dynode performance
  5. Bench test setup
  6. Dynamic readout range
  7. Anode performance
  8. Case study of impacts of muon signals in RELICS
  9. Recovery time after muon S1
  10. Waveform fidelity for muon S2
  11. Discussion and conclusion
  12. LED configuration

Figures (11)

  • Figure 1: The schematic diagram of a cosmic-ray muon traversing through the RELICS LXe TPC, producing the initial S1 and S2 signals (waveforms not to scale). Delayed emission of single- and few-electron follows the initial ionization signal by muons, which shows both position and time correlations.
  • Figure 2: The dynamic readout PMT base circuit designed for the RELICS experiment. The RELICS PMTs are positively-biased with an input voltage of $\sim800V$. A decoupler (not shown here) is needed for the anode output (Anode_Output) for a regular-gain signal; the low-gain signal is acquired from the seventh dynode (Dy7_Output).
  • Figure 3: The box diagram of the bench test setup. The R8520-406 PMT with anode and dynode readout is used to test the dynamic readout range of the base, and another is placed oppositely with a light attenuator as the monitoring PMT independently. The LED is set in the middle as the light source, which is wrapped by a Teflon sphere to ensure the light emission is as uniformly distributed as possible over the entire $4\pi$ solid angle, driven by a functional pulse generator. A synchronous trigger signal produced by the pulse generator output channel is sent to the digitizers under external trigger mode data acquisition. Data were recorded by the CAEN V1725SB digitizer with $250MS\per s$ sampling rate, 14-bit resolution, and $2V$ dynamic range.
  • Figure 4: The waveforms shown include signals from the anode (light red), dynode (light blue), and monitor (light purple) PMT readout channels, recorded at an LED driver voltage of $1.58V$. The shaded region represents a fluctuation of the waveform of each channel. The waveform from the dynode is reversed polarity for comparison with the anode and monitor waveforms.
  • Figure 5: The dynamic readout range of R8520-406 and base under different incident light intensities. The green-related data points with errors are the readout light intensity from the dynode. The black data points are related to the anode, and the $x$-axis of incident light intensity is calibrated by the monitoring PMT. The red (purple) dashed line is related to the average charge density of muon S1 (S2).
  • ...and 6 more figures