Proposal for continuation of UK participation in the International Muon Ionization Cooling Experiment

中微子是三个不同但相关的粒子；它们相互转化的能力让物理学家们第一次瞥见了他们知道必须超出标准模型的物理学。研究它们的物理性质将加深我们对宇宙在大爆炸后如何发展的理解；目前物质和反物质之间的不对称是如何从大爆炸中同等数量的物质创造出来的；并帮助我们理解当超新星爆炸时会发生什么，向宇宙注入行星和生命本身形成所需的重元素。为了了解它们的性质，我们必须建造一台能够产生巨大数量的中微子的加速器。它们的能量必须在明确定义的极限之间，不同类型的混合物必须非常精确地知道。这种被称为中微子工厂的设施将是革命性的，无论是从必须建造的粒子探测器的角度来看，还是从必须克服的工程问题的角度来看，建造一个中微子工厂都是一个具有挑战性的项目。这个项目需要全球范围的合作，但这是一个由来自英国的物理学家和工程师发挥主导作用的项目。中微子是由一束介子产生的，而介子本身是由质子与金属靶碰撞产生的介子衰变而产生的。一台制造强中微子束的机器需要获得体积较大、发散迅速的µ子束，并减小其大小和发散度。产生的光束可以被加速、储存，当它衰变时会产生一束强烈的中微子。MICE是牛津郡卢瑟福·阿普尔顿实验室的一项国际合作项目，它使用ISIS加速器产生的一束µ子，旨在证明创造出如此强的束流是可行的。MICE是一个国际合作组织，总部设在牛津郡的卢瑟福·阿普尔顿实验室。它将通过创建一个强度低得多的Muon束来实现这一点，并通过中微子工厂为执行这种束流压缩而设计的系统的一个部分单独跟踪每个Muon。在这个过程中，缪子的随机横向运动被减少，而我们只剩下纵向运动，这一过程被称为冷却光束；执行冷却的系统被称为冷却通道。第一阶段是建立一个系统，能够在进入冷却通道之前产生尺寸和发散可以调整的µ子束。这项工作已于去年完成，并进行了测量，表明光束具有足够的灵活性和强度，可供老鼠进行所需的测量。第二阶段是完成冷却通道本身的建造，并提供一个系统，非常准确地测量每个介子在穿过冷却通道之前和之后的位置和动量。通过观察在许多不同条件下产生的许多介子，就有可能确定该通道产生了多少冷却。在通道本身，通过合适的材料，如液氢、液氦或氢化锂，会使介子减慢。当它们减速时，它们在纵向和横向上都失去了相对于光束轴的动量。然后，它们被高场射频腔加速，只取代纵向动量。这项实验正在突破材料、磁体和冷却技术可能实现的极限，代表着粒子物理学家和加速器物理学家之间的合作，并将展示英国主办科学和工程前沿实验的能力。

Neutrinos are three different but related particles; their ability to turn into each other has given physicists their first glimpse of the physics which they know must lay beyond the Standard Model. Investigation of the physics which underlies their properties will: deepen our understanding of how the Universe developed after the Big Bang; how the current asymmetry between matter and anti-matter developed from a situation where they were created in equal amounts in the Big Bang; and help us to understand what happens when a supernova explodes showering the cosmos with the heavy elements necessary for planets and life itself to form. In order to understand their properties, we must build an accelerator capable of creating neutrinos in immense numbers. They must have energy between well-defined limits and the mixture of different types must be very precisely known. Such a facility, known as the Neutrino Factory, would be revolutionary and to build one is a challenging project, both from the point of view of the particle detectors which must be built, and the engineering problems which must be overcome. This programme needs a world-wide collaboration, but it is one in which physicists and engineers from the UK are playing a leading role.Neutrinos are created from a beam of muons and the muons themselves are produced from the decay of pions produced by the collision of protons with a metal target. A machine to make an intense beam of neutrinos needs to take the beam of muons, which is large and diverges rapidly, and reduce its size and divergence. The resulting beam can be accelerated, stored and when it decays produces an intense beam of neutrinos. The muons only live for 2.2 microseconds when at rest, and even when they are accelerated and their lifetime is extended by the effect of relativity, there is little time to manipulate the muons so that they are in a state to be accelerated.MICE is an international collaboration based at the Rutherford Appleton Laboratory in Oxfordshire, which uses a beam of muons created by the ISIS accelerator and aims to show that it is feasible to create such an intense beam. It will do this by creating a beam of muons of much lower intensity and tracking each one individually through one part of the system which has been designed to perform this beam compression at the Neutrino Factory. This process where the random sideways motions of the muons are reduced and we are left with the longitudinal motion is referred to as cooling the beam; the system which performs the cooling is known as the cooling channel.The first stage was to build a system capable of producing a muon beam whose size and divergence could be adjusted before it enters the cooling channel. This was completed last year and measurements have been made to show that the beam has the flexibility and intensity for MICE to perform the required measurements.The second stage is to finish construction of the cooling channel itself and to provide a system to measure very accurately the position and momentum of each muon before and after it has passed through the cooling channel. By looking at many muons produced in many different conditions, it will be possible to determine how much cooling has been produced by the channel. In the channel itself the muons will be slowed by passing through a suitable material, such as liquid hydrogen, liquid helium or lithium hydride. As they slow they lose momentum both longitudinally and transversely to the beam axis. Then they are accelerated with high field radio frequency cavities, replacing only the longitudinal momentum.This experiment which is pushing the boundaries of what is possible with materials, magnets and cooling technologies, represents a collaboration between particle physicists, and accelerator physicists and will demonstrate the UK's ability to host an experiment at the forefront of science and engineering.