Manchester Experimental Nuclear Physics Consolidated Grant Request 2011

核物理学的目标是了解核系统的结构和动力学。这是通过恒星和星系形成的历史来理解宇宙的关键，在恒星和星系形成的历史中，核反应在能量的产生和元素的创造中发挥着关键作用。从医学和安全到电力生产，该领域的应用造福了社会，并对其他科学领域产生了强烈影响。曼彻斯特集团在国际层面上做出了领先的贡献。实验工作在海外特定的设施中进行，集中投资于进行这项工作所需的仪器。实验：原子核是一个独特的量子实验室，可以在其中研究由有效的二体和三体作用力驱动的微观和介观特征。它们是复杂的多体系统，但通常表现出意想不到的规律和简单的激发模式，这些模式源于底层的壳结构、配对和集体激发模式。更简单的介观系统(例如，金属团簇、量子点和原子凝聚体)也表现出这样的性质，对这些系统的理解在很大程度上依赖于核物理中开发和磨练的技术。一个根本的挑战是从单个核子之间的强、弱和电磁力的相互作用中从头开始理解核属性。最近，针对轻核的这类计划取得了巨大进展。对于较重的核、壳层、团簇和其他超出平均场的多体技术，基于有效的相互作用，为关联实验数据提供了基本的框架，但仍然缺乏精细化来可靠地预测核性质，因为人们从研究得很好的稳定核中移动了几个以上的核子。唯一的是，放射性束流设施允许在N(中子数)、Z(质子数)、T(温度或激发能)和I(角动量)。曼彻斯特小组将解决的关键开放问题包括：*新形式的集体运动是否发生在远离核稳定谷的地方？*量子态的有序性，以及由此对核结构和反应的所有影响，在高度稀薄或富中子的物质中是如何改变的？理论：为了在最轻、最简单的原子核的结构和性质与描述核子之间强大作用力的基本理论之间建立精确的联系，量子色动力学。这是困难的，因为互动的强度。甚至它的基本自由度，夸克和胶子，也不是我们在原子核中看到的。由于该理论不能在与核物理相关的情况下得到解决，我们使用“有效的”场论，这种场论建立在适当的自由度之上，但包含了来自基本理论的强有力的约束，特别是它的对称性。一个有效的理论不应该在基础物理开始得到解决的短距离内使用。我们应用截止点来掩盖短距离行为；然后使用重新正规化方法来确保预测不依赖于截止点尺度。这种方法对于光子和介子与单核子的耦合以及一对核子之间的作用力是很好的发展的。我们现在希望将这种方法扩展到更大的原子核，最初着眼于具有3-4个核子的原子核。我们将从有效理论提供的力出发，用一种强大的变分方法来确定核波函数。有了这些波函数，我们将计算光子与这些原子核的相互作用，以了解更多关于核子如何响应外场的信息。对这些原子核的实验可以告诉我们中子的性质，因为它是一种不稳定的粒子，所以无法通过其他方法获得。

Nuclear Physics aims to understand the structure and dynamics of nuclear systems. It is key to understanding the Universe from the first microseconds of its inception through its history of star and galaxy formation where nuclear reactions play a key role in the generation of energy and the creation of elements. The field has applications that benefit society in areas from medicine and security to power production, and a strong impact on other fields of science.The Manchester group makes leading edge contributions at an international level. Experimental work is performed at specific overseas facilities with focussed investment in the necessary instrumentation to carry out this work.Experiment:Atomic nuclei are a unique quantal laboratory in which microscopic as well as mesoscopic features, driven by effective two-body and three-body forces, can be studied. They are complex many-body systems, but often display unexpected regularities and simple excitation patterns that arise from underlying shell structure, pairing and collective modes of excitation. Such properties are also exhibited by simpler mesoscopic systems (for example, metallic clusters, quantum dots, and atomic condensates) the understanding of which draws heavily on techniques developed and honed in nuclear physics. A fundamental challenge is to understand nuclear properties ab-initio from the interplay of the strong, weak, and electromagnetic forces between individual nucleons. Recently, enormous progress has been made with such programmes for light nuclei. For heavier nuclei, shell, cluster and other beyond mean field many-body techniques, based on effective interactions, provide essential frameworks for correlating experimental data, yet still lack the refinement to reliably predict nuclear properties as one moves more than a few nucleons from well-studied stable nuclei.Uniquely, radioactive beam facilities allow an exploration of nuclear properties using both approaches over a wide range of N (neutron number), Z (proton number), T (temperature or excitation energy) and I (angular momentum).The key open questions the Manchester group will address include:* Do new forms of collective motion occur far from the valley of nuclear stability? * How does the ordering of quantum states, with all of its consequent implications for nuclear structure and reactions, alter in highly dilute or neutron-rich matter? Theory:To make precise connections between the structure and properties of the lightest, simple atomic nuclei and the underlying theory that describes the strong forces between nucleons, Quantum Chromodynamics. This is difficult because of the strength of the interaction. Even its fundamental degrees of freedom, quarks and gluons, are not the ones we see in nuclei. As the theory cannot be solved for situations relevant to nuclear physics, we work with "effective" field theories, built out of the appropriate degrees of freedom but incorporating robust constraints from the underlying theory, in particular its symmetries. An effective theory shouldn't be used at short distances where the underlying physics starts to be resolved. We apply a cut-off to mask the short-distance behaviour; a renormalisation approach is then used to ensures that predictions do not depend on cut-off scale. This approach is well-developed for couplings of photons and pions to single nucleons and for the forces between a pair of nucleons. We now wish to extend the approach to larger nuclei, initially looking at ones with 3-4 nucleons. We will use a powerful variational method to determine the nuclear wave functions, starting from forces provided by the effective theories. With these wave functions, we will then calculate interactions of photons with these nuclei to learn more about how nucleons respond to external fields. Experiments of these nuclei can tell us about the properties of the neutron, which are not accessible by other means since it is an unstable particle.