Electrons for neutrinos

电子换中微子

• 批准号: ST/T002425/1
• 负责人: Daniel Watts
• 金额: $ 14.38万
• 依托单位: University of York
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2019
• 资助国家: 英国
• 起止时间: 2019 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=ST%2FT002425%2F1
• 关键词: Electrons; neutrinos

Neutrinos are ethereal particles which are extremely difficult to detect. They have a high abundance in the universe (around a trillion neutrinos pass through the average person every second), but having masses less than a millionth that of an electron and only interacting via the weak force and gravity, their probability of interaction is very small. In fact, neutrinos can pass through the entire diameter of the earth without interaction!So how one can observe and study these ethereal particles at all in terrestrial experiments? The solution is to construct a detector that is made up of as large a volume of material as possible and to produce neutrino beams with incredibly intense flux. Such facilities are operational and exciting new facilities are planned. For example, in the Deep underground Neutrino Experiment (DUNE) under construction, neutrinos produced at Fermilab will pass 800 miles through the earths mantle to another laboratory in Sanford, where detectors comprise 40 tonnes of liquid Argon! The rare interactions of neutrinos in detectors are obtained by examining the reaction products produced (usually with detection of a knocked-out proton) when a neutrino interacts with an atomic nucleus. The energy of the neutrino that produced the reaction is then inferred by nuclear reaction theoretical models. The problems stem from the fact that the atomic nuclei used for this purpose need to be large in order to get enough neutrino induced events; for example the Argon at Dune has 40 protons and neutrons in it's nucleus. A large nucleus is a very complicated object and the modelling of the reaction processes is very difficult with lots of outstanding questions: Can we suppress events where the knocked out nucleon scattered on it's way out of the nucleus? How well can we suppress contributions where the neutrino is absorbed on more than one nucleon and we only detect one? Producing a pion from a nucleon has a similar probability to knockout, but how well can we suppress these erroneous events in the experimental data? Can we get rid of processes where a pion (or pions) are initially produced in the nucleus and then reabsorbed to knock out nucleons? What about if we excite a nucleon in the reaction mechanism, and how do such excited nucleons behave in the nucleus? These are merely a small set of outstanding questions that directly impact the determination of the incident neutrino energy and flux.In our programme we will use an analogous reaction to the neutrino-nucleus interactions: we will scatter electrons off the nuclei rather than neutrinos. This has the advantage that we get many orders of magnitude more events to test the models and very importantly, in a controlled way! By knowing the incident electron energy, all the assumptions in getting from nuclear fragments to the beam energy for a whole host of reactions and a wide range of nuclei becomes accessible. This data set is urgently needed to reduce errors in the theoretical modelling; these errors typically produce the largest systematic error for the neutrino experiments. By using common theoretical models for the neutrino- and electron-induced reactions we can challenge the models and improve the modelling of various processes at a level of details that was previously impossible. This then reduces significantly any systematic errors in extracting physics from the next generation neutrino facilities. Progress requires a major programme of analysis of existing, as well as planned electron scattering experiments from nuclei with complex detector systems at Jefferson Laboratory (USA). We will construct a new analysis framework, which will be used to analyse and archive data in a form that makes it readily accessible and flexible for use by nuclear and particle communities for decades to come. The work will be carried out as part of a new collaborative network including colleagues at MIT, ODU, Jefferson Lab and Tel Aviv University.

中微子是一种极难探测到的无形粒子。它们在宇宙中有很高的丰度（平均每秒约有1万亿个中微子通过），但质量不到电子的百万分之一，并且只通过弱力和引力相互作用，它们相互作用的概率非常小。事实上，中微子可以穿过地球的整个直径而不发生相互作用！那么，如何在地球实验中观察和研究这些空灵的粒子呢？解决方案是建造一个由尽可能大的材料体积组成的探测器，并产生具有令人难以置信的强通量的中微子束。这些设施已经投入使用，令人兴奋的新设施正在规划中。例如，在正在建设的深层地下中微子实验（DUNE）中，费米实验室产生的中微子将穿过800英里的地幔到达桑福德的另一个实验室，那里的探测器包括40吨液态氩！中微子在探测器中的罕见相互作用是通过检测中微子与原子核相互作用时产生的反应产物（通常是检测到被击倒的质子）来获得的。产生反应的中微子的能量然后由核反应理论模型推断。问题源于这样一个事实，即用于此目的的原子核需要很大，以便获得足够的中微子诱发事件;例如，沙丘的氩气在其原子核中有40个质子和中子。一个大的原子核是一个非常复杂的物体，反应过程的建模非常困难，有许多悬而未决的问题：我们能抑制被击倒的核子在离开原子核的途中散射的事件吗？如果中微子被多个核子吸收，而我们只探测到一个核子，那么我们能在多大程度上抑制中微子的贡献？从核子中产生π介子的概率与敲除π介子的概率相似，但我们能在多大程度上抑制实验数据中的这些错误事件呢？我们能摆脱最初在原子核中产生π介子（或π介子），然后被重吸收而撞出核子的过程吗？如果我们在反应机制中激发一个核子会怎样？这样的激发核子在原子核中又是如何表现的？这些只是一小部分直接影响入射中微子能量和通量测定的悬而未决的问题。在我们的计划中，我们将使用类似于中微子-核相互作用的反应：我们将从核散射电子而不是中微子。这样做的好处是，我们可以得到更多数量级的事件来测试模型，而且非常重要的是，以一种可控的方式！通过知道入射电子能量，从核碎片到束流能量的所有假设对于整个反应和广泛的核变得容易。迫切需要这组数据来减少理论建模中的误差;这些误差通常会产生中微子实验的最大系统误差。通过使用中微子和电子诱导反应的共同理论模型，我们可以挑战模型，并在以前不可能的细节水平上改进各种过程的建模。这就大大减少了从下一代中微子设施中提取物理学的任何系统误差。要取得进展，就需要在杰斐逊实验室（美国）用复杂的探测器系统对现有的和计划中的原子核电子散射实验进行分析。我们将构建一个新的分析框架，用于分析和存档数据，使其易于访问和灵活，供核和粒子界在未来几十年使用。这项工作将作为一个新的合作网络的一部分进行，该网络包括麻省理工学院，ODU，杰斐逊实验室和特拉维夫大学的同事。

项目成果

Electron-beam energy reconstruction for neutrino oscillation measurements.

用于中微子振荡测量的电子束能量重建。

• DOI: 10.1038/s41586-021-04046-5
• 发表时间: 2021
• 期刊: Nature
• 影响因子: 64.8
• 作者: Khachatryan M