Manchester Experimental Nuclear Physics Consolidated Grant Request 2011

核物理学旨在了解核系统的结构和动力学。它是理解宇宙的关键，从宇宙诞生的第一微秒到星星和星系形成的历史，核反应在能量的产生和元素的创造中发挥着关键作用。该领域的应用造福于社会，从医学和安全到电力生产，并对其他科学领域产生重大影响。曼彻斯特集团在国际层面上做出了领先的贡献。实验：原子核是一个独特的量子实验室，在有效的二体和三体力的驱动下，可以研究微观和介观的特征。它们是复杂的多体系统，但经常显示出意想不到的非线性和简单的激发模式，这些模式来自底层的壳结构、配对和集体激发模式。这种性质也表现在更简单的介观系统（例如，金属团簇，量子点和原子凝聚体）中，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。一个基本的挑战是从单个核子之间的强、弱和电磁力的相互作用从头开始理解核性质。最近，轻核的这类方案取得了巨大进展。对于较重的核，壳层、团簇和其他基于有效相互作用的超平均场多体技术为关联实验数据提供了必要的框架，但仍然缺乏精确的方法来可靠地预测核性质，因为人们从充分研究的稳定核中移动了几个以上的核子。放射性束设施允许在很宽的N范围内使用这两种方法来探索核特性。（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未决问题包括：* 在远离核稳定性谷的地方会出现新形式的集体运动吗？* 在高度稀释或富含中子的物质中，量子态的有序性，以及它对核结构和反应的所有影响，是如何改变的？理论：在最轻，简单的原子核的结构和性质与描述核子之间强作用力的基础理论量子色动力学之间建立精确的联系。这是困难的，因为相互作用的强度。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。由于该理论无法解决与核物理相关的情况，我们使用“有效”场论，建立在适当的自由度之外，但结合了基础理论的强大约束，特别是其对称性。一个有效的理论不应该被用在短距离上，因为那里的基础物理学开始被解决。我们应用一个截止掩盖短距离的行为，然后使用一个重正化的方法，以确保预测不依赖于截止尺度。这种方法对于光子和π介子与单个核子的耦合以及一对核子之间的力是很好的发展。我们现在希望将这种方法扩展到更大的原子核，首先研究具有3 - 4个核子的原子核。我们将使用一个强大的变分方法来确定核子波函数，从有效理论提供的力开始。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部场的信息。这些核的实验可以告诉我们中子的性质，这是通过其他手段无法获得的，因为它是一种不稳定的粒子。

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.