标题： PIKACHU项目160Gd双β衰变搜索的仿真工具开发与敏感性分析 显示英文标题

标题： Simulation Tool Development and Sensitivity Analysis of 160Gd Double Beta Decay Search by the PIKACHU Project

摘要： 中微子无中微子双β衰变（0v2b）已被研究作为一种可以提供中微子马约拉纳性质证据的物理过程。 0v2b速率的理论预测受到显著的不确定性影响，主要是由于核矩阵元（NME）。 为了减少这种不确定性，对各种核素的两中微子双β衰变（2v2b）的半衰期进行实验测量是必要的，作为NME计算的基准。 PIKACHU（纯无机闪烁体实验在 Kamioka 用于挑战地下科学）项目旨在寻找此前未被观测到的160Gd的2v2b衰变，采用掺铈的Gd3Ga3Al2O12（GAGG）单晶。 在第一阶段实验中，我们希望通过使用掺铈的Gd2SiO5（GSO）晶体的前期研究，提高当前对160Gd 2v2b半衰期的下限。 最终，在第二阶段，该项目旨在实现超越理论预测的7.4 x 10^20年的灵敏度，从而有可能发现160Gd的2v2b衰变。 在本文中，我们描述了基于GEANT4模拟的背景模型的发展。 所建模的背景包括铀和钍衰变链的贡献、GAGG中存在的40K以及来自GAGG外部的40K伽马射线。 此外，我们通过在GEANT4模拟中实现双β衰变中两个电子发射的理论运动学，开发了2v2b和0v2b衰变的模型。 结果表明，我们的背景模型通过拟合成功地再现了测量的背景谱。 通过生成第一阶段预期的伪背景谱，并用结合的背景和2v2b模型对其进行分析，我们评估了第一阶段的2v2b灵敏度为2.78 x 10^19年（90%置信水平）。 本文介绍了这些模拟模型的发展以及基于伪数据分析的第一阶段和第二阶段的预期灵敏度。 显示英文摘要

摘要： Neutrinoless double beta decay (0v2b) has been investigated as a physical process that can provide evidence for the Majorana nature of neutrinos. The theoretical predictions of the 0v2b rate are subject to significant uncertainty, primarily due to nuclear matrix elements (NME). To reduce this uncertainty, experimental measurements of the half-lives of two-neutrino double beta decay (2v2b) in various nuclei are essential as a benchmark for NME calculations. The PIKACHU (Pure Inorganic scintillator experiment in KAmioka for CHallenging Underground sciences) project searches for the previously unobserved 2v2b decay of 160Gd, employing Ce-doped Gd3Ga3Al2O12 (GAGG) single crystals. In the Phase 1 experiment, we aim to improve the current lower limit on the 2v2b half-life of 160Gd by a prior study using a Ce-doped Gd2SiO5 (GSO) crystal. Ultimately, in Phase 2, the project seeks to achieve a sensitivity surpassing the theoretical prediction of 7.4 x 10^20 years, enabling the potential discovery of the 160Gd 2v2b decay. In this paper, we describe the development of background models based on GEANT4 simulations. The modeled backgrounds are contributions from uranium and thorium decay chains, 40K present in GAGG, and 40K gamma-rays from outside of GAGG. Additionally, we developed models for both 2v2b and 0v2b decay by implementing the theoretical kinematics of two-electron emission in double beta decay in the GEANT4 simulation. As a result, our background models successfully reproduced the measured background spectrum through fitting. By generating pseudo background spectra expected in Phase 1 and analyzing them with the combined background and 2v2b models, we evaluated the 2v2b sensitivity of Phase 1 to be 2.78 x 10^19 years (90% C.L.). This paper presents the development of these simulation models and the expected sensitivities for both Phase 1 and Phase 2 based on the pseudo data analyses.