MICE-UK & UKNF Programmes

目前物理上已知的粒子种类，即中微子，有三种类型：电子、介子和介子，可能是最耐人寻味但最不为人所知的。中微子的质量很小，与物质的相互作用非常弱。到目前为止，所有粒子物理实验的结果都可以很容易地用20世纪60年代发展起来的粒子物理的“标准模型”来解释：除了少数几个研究中微子行为的实验的一小部分结果。中微子在恒星和地球大气层中自然不断地产生。探测这些中微子的实验一直发现比产生的中微子少。最近，涉及人造中微子的实验也展示了类似的中微子振荡行为。对于自然界中的每一种粒子类型，都有一个相应的反粒子类型--这些反粒子一起被称为反物质。特别令人感兴趣的是反中微子的振荡是否与中微子的振荡相同的问题。这个问题被认为与这样一个事实有关，即今天的宇宙几乎完全由物质组成，而大爆炸应该创造出等量的物质和反物质。反物质去向的谜团可以用中微子和反中微子振荡行为的不同来解释。这个问题只能通过使用高强度人造中微子束对中微子振荡进行超灵敏测量来回答。这项研究的最终目标是在“中微子工厂”中产生人类有史以来最强的中微子束。这些中微子束将以不同的角度穿过地球。这将使我们能够比以往任何时候都更精确地确定中微子的性质，并使我们能够回答中微子和反中微子的振荡是否相同的根本问题。这应该会解开大爆炸中产生的反物质去了哪里的谜团，从而有助于解释我们今天所知的宇宙的存在。中微子工厂将从被称为µ子的母体粒子的衰变中产生强烈的中微子。在实现中微子工厂之前，有许多重要的问题必须解决。首先，必须处理生产足够的质子束的问题。其次，有必要开发新的技术来非常迅速地加速介子，因为介子的衰变寿命(静态)为2.2微秒。其中最重要的问题之一是在进入Muon加速系统之前挤压(冷却)Muon束所占据的空间体积。通常用于冷却粒子束的技术不能用于介子，因为它们衰变成中微子的速度很快。开发一种名为“电离冷却”的新技术是至关重要的。如果一束介子穿过物质，介子就会减慢速度。如果它们随后在同一方向上被重新加速，光束的大小和扩散将会减小。如果这个过程重复多次，光束就可以变得足够窄，足够平行，可以放入储存环中。英国卢瑟福·阿普尔顿实验室的Muon电离冷却实验(MICE)旨在首次演示Muon的电离冷却。它由一个短小的“冷却部分”和一个“腔”组成，其中包含“吸收体”和“空腔”，在“吸收体”中，介子会损失能量，而“腔”中，介子被高电场加速。这些介子将由超导磁铁产生的强磁场引导。介子束穿过冷却部分之前和之后的大小将被测量。由于冷却段短，冷却效果将相当小，前后测量必须以千分之一的精度进行。

The species of particles currently known to physics, the neutrinos, which come in three types: electron, muon, and tau, are probably among the most intriguing but least understood. The neutrinos have tiny masses and interact with matter only very weakly. The results of all particle physics experiments to date have been readily explained by the 'Standard Model' of particle physics, developed in the 1960s: that is, except, for a small set of results from a select few experiments investigating the behaviour of neutrinos. Neutrinos are naturally produced continuously in stars and the earth's atmosphere. Experiments to detect these neutrinos have consistently found fewer neutrinos than are produced. More recently, experiments involving man-made neutrinos have demonstrated similar neutrino oscillation behaviour. For each particle type in nature, there is a corresponding anti-particle type - the anti-particles together are known as anti-matter. Of particular interest is the question of whether the oscillations of anti-neutrinos are the same as those of neutrinos. This question is believed to be related to the fact that the universe today is composed almost entirely of matter, whereas the Big Bang should have created equal amounts of matter and anti-matter. The mystery of where the anti-matter has gone could be explained by a difference in the oscillation behaviour of neutrinos and anti-neutrinos. This question can only be answered by making ultra-sensitive measurements of neutrino oscillations using high-intensity man-made beams of neutrinos. The ultimate goal of the proposed research is to produce the most intense beams of neutrinos ever created by man in a 'Neutrino Factory'. These beams of neutrinos will be directed at various angles through the Earth. This will allow the properties of the neutrinos to be determined far more precisely than ever before, and will allow us to answer the fundamental question of whether the oscillations of neutrinos and anti-neutrinos are the same or not. This should solve the puzzle of where the anti-matter created at the Big Bang has gone, and therefore help to explain the existence of the universe as we know it today. The Neutrino Factories will produce intense neutrino from the decay of parent particles called muons. There are a number of important issues that must be addressed before the Neutrino Factory can be realized. First, the issue of producing sufficient proton-beam must be dealt with. Second it is necessary to develop novel techniques to accelerate the muons very rapidly since muons decay with a lifetime (at rest) of 2.2 microseconds. One of the most important problems is that of squeezing down (cooling) the volume of space occupied by the muon beam before it enters the muon-acceleration system. The commonly used techniques for cooling beams of particles cannot be used for muons because they decay to neutrinos so quickly. The development of a new technique called 'ionisation cooling' is essential. If a beam of muons is passed through material the muons will slow down. If they are then reaccelerated in the same direction, the size and spread of the beam will be reduced. If this process is repeated many times, the beam can be made narrow and parallel enough to fit into a storage ring. The Muon Ionisation Cooling Experiment (MICE) at the Rutherford Appleton Laboratory in the UK aims to demonstrate the ionisation cooling of muons for the first time. It consists of a short 'cooling section' which contains 'absorbers' where the muons lose energy and 'cavities' where the muons are accelerated by high electric fields. The muons will be guided by strong magnetic fields from superconducting magnets. The size the muon beam will be measured before and after it has passed through the cooling section. Because the cooling section is short the cooling effect will be quite small and the before- and-after measurements must be made with a precision of one part in a thousand.