PREX ll and CREX: Precision parity violating measurement of neutron skin of heavy nuclei at Jefferson Laboratory

PREX ll 和 CREX：杰斐逊实验室重核中子皮的精确宇称破坏测量

• 批准号: SAPPJ-2019-00050
• 负责人: Mammei, Juliette
• 金额: $ 11.29万
• 依托单位: University of Manitoba
• 依托单位国家: 加拿大
• 项目类别: Subatomic Physics Envelope - Project
• 财政年份: 2021
• 资助国家: 加拿大
• 起止时间: 2021-01-01 至 2022-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=739459
• 关键词: PREX; ll; CREX; Precision; parity

"How do the protons and neutrons fit together to make a nucleus?" is one of the most fundamental questions that a nuclear structure theory could answer.  It has truly far-reaching consequences, both for a large range of fields in physics and also literally far-reaching - by telling us about the structure of neutron stars. LIGO has given us a new window on the universe by observing gravitational waves from neutron star mergers. In order to fully understand the results from these measurements, the Pb Radius Experiment (PREX II) and the Ca Radius Experiment (CREX) will provide information about the properties of neutron matter.  The difference between the radius of neutrons and protons in a nucleus has direct consequences for the structure of neutron stars, affecting how big they can be, how thick their crusts are and how long they will take to cool. This information will also help us predict whether a star will collapse into a neutron star or a black hole. The "textbook" size of a nucleus is the electric charge distribution - measured extremely well in electron scattering at different kinematics and then used to obtain the charge radius. By measuring the form factor of the nucleus at different four-momentum transfer, and then taking the Fourier transform, you can obtain the density of charge within the nucleus as a function of radius. What this tells you is the distribution of protons within the nucleus, because the proton is what gives the nucleus its electric charge. But the question remains whether the distribution of neutrons is the same as that of the protons. North America's premier electron scattering facility, Jefferson Laboratory, is the ideal place to find the answer to this question. PREX II and CREX will measure the neutron radius of specific isotopes of both lead (Pb) and calcium (Ca) using the property of parity violation in the weak interaction to measure the weak charge of the nucleus. Parity violation is analogous to the scattering being different when it is observed in a mirror. Because the proton has almost no weak charge, while the neutron has maximum weak charge, measuring the weak charge distribution tells you the neutron distribution. Jefferson Lab's electron accelerator makes the electrons travel greater than 0.99999 times the speed of light. The detectors work because the electrons are actually traveling faster than light in the quartz that makes up the active area, causing them to emit Cherenkov radiation. The asymmetry we measure is smaller than the concentration of 4 drops of ink in a 55 gallon barrel of water! The PREX II and CREX collaborations consist of over 20 institutions world-wide with over 50 collaborators. Our Canadian group will play a key role in the PREX II and CREX experiments through design, construction, testing and deployment of key pieces of equipment including simulation of backgrounds and design of detectors used to measure the degree of polarization of the electron beam.

“质子和中子如何组合在一起形成原子核？”是核结构理论可以回答的最基本的问题之一，它对物理学和许多领域都具有真正深远的影响。意义深远——通过观察中子星合并产生的引力波，LIGO 为我们提供了了解宇宙的新窗口。为了充分理解这些测量结果，Pb 半径实验。 (PREX II) 和 Ca 半径实验 (CREX) 将提供有关中子物质性质的信息​ 原子核中中子和质子半径的差异对中子星的结构有直接影响，影响中子星的大小。 ，它们的外壳有多厚以及它们需要多长时间才能冷却，这些信息也将帮助我们预测恒星是否会塌缩成中子星或黑洞。核的“教科书”大小是电荷分布。 - 测量的不同运动学下的电子散射效果非常好，然后用于获得电荷半径 通过测量不同四动量传递下的原子核的形状因子，然后进行傅里叶变换，可以获得原子核内的电荷密度：这告诉你的是原子核内质子的分布，因为质子赋予原子核电荷，但问题仍然是中子的分布是否与北美的质子分布相同。首映杰斐逊实验室电子散射设施是寻找此问题答案的理想场所，PREX II 和 CREX 将利用宇称破坏特性来测量铅 (Pb) 和钙 (Ca) 特定同位素的中子半径。弱相互作用来测量原子核的弱电荷，类似于在镜子中观察时的散射不同，因为质子几乎没有弱电荷，而中子具有最大的弱电荷，测量弱电荷分布。你杰斐逊实验室的电子加速器使电子的行进速度大于光速的 0.99999 倍，因为电子实际上在构成活性区域的石英中行进速度比光快，从而导致它们发射切伦科夫辐射。我们测量的不对称性小于 55 加仑桶水中 4 滴墨水的浓度 PREX II 和 CREX 合作由全球 20 多个机构组成！我们的加拿大团队拥有 50 多名合作者，将通过设计、建造、测试和部署关键设备（包括背景模拟和用于测量偏振度的探测器设计）在 PREX II 和 CREX 实验中发挥关键作用。电子束。