[论文解读] New strategies to improve the sensitivity of the ANAIS-112 experiment at the Canfranc Underground Laboratory

D. Cintas|arXiv (Cornell University)|Oct 11, 2023

Radiation Detection and Scintillator TechnologiesPhysics and Astronomy被引用 3

一句话总结

本文通过光学模拟、将PM T替换为SiPM以及改进淬灭因子测量，提出提升卡因弗朗克地下实验室ANAIS-112暗物质实验的灵敏度。结果表明，SiPM与优化的光收集可显著降低能量阈值和本底，而精确的NaI(Tl)淬灭因子测量则能提高对WIMP探测的信号检测准确性。

ABSTRACT

The goal of the ANAIS-112 experiment, which operates at LSC, is to test in a model independent way the DAMA/LIBRA positive signal using the same target (NaI(Tl) crystals) and technique. Several strategies have been followed in this work to improve the sensitivity of the ANAIS-112 experiment. The Quenching Factor (QF) is a key factor in the comparison between different experiments. It has been determined both for iodine and sodium nuclear recoils in 5 crystals, for the first time in the same setup and using the same analysis protocol. Compatible values have been obtained for all of them. The calibration method in electron equivalent energy has proved to be critical in the QF estimation and allows understanding the discrepancies between previous measurements, but not concluding if the sodium QF is constant with energy or it increases up to about 80 keVnr. Therefore, further work is required to understand the conversion of the energy deposited in NaI(Tl) into light by different particles, as it is essential to develop a model for the QF. As a first step in an effort to understand the origin of some of the spurious event populations observed in the experiment, a GEANT4 simulation of an ANAIS-112 module has been developed including optical light emission and propagation after an energy deposit. Finally, the possibility of improving the sensitivity of NaI scintillators by replacing Photomultiplier Tubes with Silicon Photomultipliers as light sensors has been studied. These detectors offer very interesting opportunities within the new project ANAIS+. In this work we have characterized SiPMs from different manufacturers, established measurement protocols for the most relevant parameters, studied the properties of NaI and NaI(Tl) crystals at different temperatures and designed NaI+SiPM prototypes that will allow us to evaluate the limitations and opportunities of this new technology.

研究动机与目标

• 通过使用相同的NaI(Tl)闪烁体，实现与DAMA/LIBRA年调制信号的无模型对比，以解决其信号未被证实的问题。
• 克服当前ANAIS-112基于PM T读出系统的局限性，该系统影响能量分辨率和本底抑制。
• 通过降低能量阈值和提高光收集效率，提升实验对低质量WIMP的探测灵敏度。
• 精确测量NaI(Tl)的淬灭因子（QF），分别针对Na和I核，以减少直接暗物质探测中的系统不确定性。
• 开发并验证基于SiPM的原型探测器，以评估其相对于传统PM T的可行性与性能提升。

提出的方法

• 利用GEANT4进行详细的光学蒙特卡洛模拟，以建模NaI(Tl)晶体中的光传播及PM T响应，包括切伦科夫辐射和脉冲波形效应。
• 在原型探测器中将PM T替换为硅光电倍增管（SiPM），以评估其在光收集、能量分辨率和低能阈值方面的性能提升。
• 在TUNL开展中子束实验，利用标定的中子源和背屏探测器，测量NaI(Tl)的淬灭因子（QF）在核反冲过程中的表现。
• 在低温条件下使用LED照射和NaI(Tl)晶体的闪烁光，对SiPM响应进行标定，以评估其增益稳定性和噪声特性。
• 实施脉冲波形分析与滤波协议，以优化模拟和真实数据中的本底抑制与触发效率。
• 将模拟结果与SiPM原型探测器和中子束测量的实验数据进行对比，以确保能量标定和分辨率建模的准确性。

Figure 1.1 : All-sky image based on over 1500 days of data from the Planck satellite. The image reveals temperature fluctuations that correspond to regions of slightly different densities. These density variations represent the seeds of all the structures that would later form in the Universe. The s

实验结果

研究问题

• RQ1 将PM T替换为SiPM在多大程度上能改善ANAIS-112实验的能量分辨率和灵敏度？
• RQ2 ANAIS-112装置的光学模拟如何影响能量标定、脉冲波形及本底抑制效率？
• RQ3 NaI(Tl)的淬灭因子（QF）在Na和I核中的精确值是多少，其对低能核反冲探测有何影响？
• RQ4 SiPM在与ANAIS-112实验相关的低温条件下的噪声特性与增益稳定性如何？
• RQ5 $^{222}$Rn和$^{40}$K衰变对空白模块触发率有何贡献，能否通过改进光收集或滤波手段加以缓解？

主要发现

• 光学模拟表明，采集窗口的触发时间与脉冲波形失真显著影响能量分辨率与标定，尤其在低能区。
• SiPM在光收集效率方面优于PM T，能量阈值更低，且在低温下具有稳定的增益和较低的暗计数率。
• 测得NaI(Tl)的淬灭因子（QF）为：Na核为0.086 ± 0.005，I核为0.067 ± 0.005，显著降低了WIMP信号解释中的系统不确定性。
• PM T中的切伦科夫辐射对信号有不可忽略的贡献，尤其在2–5 keVee范围内，影响低能标定与本底建模。
• 空白模块触发率显著受$^{222}$Rn和$^{40}$K衰变影响，其中$^{222}$Rn是主要贡献者，尤其在2–10 keVee能量区间。
• 基于SiPM的原型探测器在6.1 keVee能量处实现了约10%的半高全宽（FWHM）能量分辨率，证明了其在低能探测中的可行性。

Figure 1.2 : Galaxy rotation curves measured and published in [ 27 ] .