Beta Spectrum Generator: High precision allowed $\beta$ spectrum shapes

Several searches for Beyond Standard Model physics rely on an accurate and highly precise theoretical description of the allowed beta spectrum. Following recent theoretical advances, a C++ implementation of an analytical description of the allowed beta spectrum shape was constructed. It implements all known corrections required to give a theoretical description accurate to a few parts in 10^4 . The remaining nuclear structure-sensitive input can optionally be calculated in an extreme single-particle approximation with a variety of nuclear potentials, or obtained through an interface with more state-of-the-art computations. Due to its relevance in modern neutrino physics, the corresponding (anti)neutrino spectra are readily available with appropriate radiative corrections. In the interest of user-friendliness, a graphical interface was developed in Python with a coupling to a variety of nuclear databases. We present several test cases and illustrate potential usage of the code. Our work can be used as the foundation for current and future high-precision experiments related to the beta decay process.多项搜寻超出标准模型物理（Beyond Standard Model Physics）的研究，均依赖于对容许β谱（allowed beta spectrum）的精准且高精度的理论描述。基于近期的理论进展，研究团队构建了容许β谱形状的解析描述的C++实现。该实现涵盖了所有必要的已知修正项，可将理论描述的精度控制在10⁴分之几的误差范围内。对于剩余的核结构敏感输入参数，既可以通过多种核势（nuclear potentials）下的极端单粒子近似（single-particle approximation）进行计算，也可通过对接更前沿的计算程序获取。鉴于其在现代中微子物理（neutrino physics）中的重要应用价值，配套的（反）中微子谱可通过合适的辐射修正（radiative corrections）便捷生成。为提升工具的易用性，研究团队基于Python开发了图形界面，并对接了多种核数据库。本文展示了多个测试用例，并演示了该代码的潜在应用场景。本研究可作为当前及未来与β衰变（beta decay）过程相关的高精度实验的研究基础。