Precision measurement of proton recoil spectrum and proton asymmetry in neutron decay using the spectrometer aSPECT (ILL contribution)

使用光谱仪 aSPECT 精确测量质子反冲光谱和中子衰变中的质子不对称性（ILL 贡献）

• 批准号: 237545110
• 负责人: Professor Dr. Oliver Zimmer
• 金额: --
• 依托单位: Institut Laue-Langevin (ILL)
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 财政年份: 2013
• 资助国家: 德国
• 起止时间: 2012-12-31 至 2018-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/237545110?language=en
• 关键词: Precision; measurement; proton; recoil; spectrum

We propose to perform accurate measurements of two neutron decay observables using the spectrometer aSPECT at the cold neutron beam facility PF1b at the ILL in Grenoble. The antineutrino-electron angular correlation coefficient “a” shall be measured via the proton recoil spectrum with an accuracy of 0.3%, and the asymmetry “C” of proton emission with respect to the neutron spin direction with accuracy 0.1%. Within the standard model of particle physics, they are both functions of the ratio of the weak axial-vector and vector coupling constants λ = gA/gV. This value is an important input to calculate many semi-leptonic weak cross sections such as those relevant for big-bang nucleosynthesis, stellar fusion and detection of neutrinos. It also enters the determination of the largest element of the CKM matrix which parameterizes mixing within the weak charged current interactions of quarks. On the other hand, both coefficients have different sensitivity to physics beyond the standard model as, e.g., scalar or tensor interactions. Our experiments will provide valuable input to global analyses of weak interaction parameters for applications and for tests of physics beyond the standard model. The spectrometer aSPECT has been developed and commissioned in collaboration of Universities from Mainz and Munich with the ILL. During the last funding period aSPECT has been equipped with a large surface silicon drift detector offering an excellent separation of the signal from noise for protons accelerated to only a few keV. The understanding of the spectrometer and its performance were significantly improved, so that aSPECT is now ready for exploitation. The proposed experiments will not only improve the knowledge of the physics observables by more than an order of magnitude but also deliver important experience for the operation of the instrument PERC under construction at the FRM II, and the design of its secondary spectrometers.

我们建议使用格勒诺布尔 ILL 的冷中子束设施 PF1b 的光谱仪 aSPECT 对两个中子衰变可观测值进行精确测量。反中微子-电子角相关系数“a”通过质子反冲能谱测量，精度为0.3%，质子发射相对于中子自旋方向的不对称性“C”测量精度为0.1%。在粒子物理的标准模型中，它们都是弱轴矢量与矢量耦合常数 λ = gA/gV 之比的函数。该值是计算许多半轻子弱截面的重要输入，例如与大爆炸核合成、恒星聚变和中微子检测相关的截面。它还涉及 CKM 矩阵最大元素的确定，该矩阵参数化夸克弱带电电流相互作用中的混合。另一方面，这两个系数对标准模型之外的物理现象具有不同的敏感性，例如标量或张量相互作用。我们的实验将为应用程序和标准模型之外的物理测试的弱相互作用参数的全局分析提供有价值的输入。光谱仪 aSPECT 是美因茨大学和慕尼黑大学与 ILL 合作开发和调试的。在上一次资助期间，aSPECT 配备了大型表面硅漂移探测器，可以将质子加速至几 keV 时的信号与噪声完美分离。对光谱仪及其性能的理解得到了显着提高，因此 aSPECT 现在已准备好进行开发。所提出的实验不仅将使物理可观测知识提高一个数量级以上，而且还为FRM II正在建设的PERC仪器的运行及其二次光谱仪的设计提供重要经验。