SuperNEMO Commissioning and Sensitivity Demonstration

中微子是宇宙中最丰富的物质粒子，然而我们对它们的认识在基本方面仍然缺乏。我们不知道中微子和反中微子是否真的是不同的粒子，或者只是同一粒子的不同版本，这是可能的，因为它们不带任何电荷。近几十年来，中微子振荡实验对中微子的风味结构，特别是中微子如何由于微小的质量差异而从一种风味转变为另一种风味，有了相当大的了解。然而，尽管我们相当精确地知道这些质量差异，我们仍然不知道中微子的绝对质量尺度是多少。当今粒子物理学最重要的任务之一是阐明围绕中微子的一些谜团。这可能会让我们进一步了解一些基本问题，如与大统一相关的极高能量的物理性质，以及我们今天在宇宙中观察到的物质-反物质不对称的来源。衰变是一种常见的放射性过程，即母核衰变为子核，同时发射电子和（看不见的）反中微子。在某些原子核中-衰变是禁止的，但在极少数情况下，可能同时发生两个-衰变。在几种同位素中已经观察到两个电子被发射的独特特征。我们正在寻找一种独特的双β衰变形式，在这种形式中，没有中微子与电子一起发射，导致电子带走了相关核衰变的全部能量。只有当中微子和反中微子是相同的基本粒子时，这种“无中微子”过程才会发生。此外，通过测量这种衰变的速率，我们可以有效地测量中微子的绝对质量。为了以前所未有的高灵敏度寻找中微子双β衰变，我们建造了世界上最大的盖革计数器。SuperNEMO实验中所谓的“追踪器”记录了电子从双β衰变中留下的电离，并使我们能够可视化它们离开探测器的轨迹。过去3年来，英国各集团一直在制造这种跟踪探测器，其基础是在此之前进行的大量研发。SuperNEMO的下一阶段是将英国制造的追踪器带到位于法国和意大利之间阿尔卑斯山下的地下实验室，以保护实验免受宇宙射线的影响。在那里，我们将把跟踪器与探测器的其他组件结合起来，这些组件正在由法国、俄罗斯、捷克共和国和美国的同事组装。要精心组装“超级nemo”的第一个模块，即“演示模块”，需要进行大量的工作，以使其按预期工作，并且不允许放射性污染进入探测器。即使是远低于普通物质放射性水平的微量污染，也可能完全淹没我们正在寻找的非常罕见的过程。在这个项目结束时，超级nemo演示模块将启动和运行，并启动到一个令人兴奋的物理程序，试图解决上面概述的一些基本问题。

Neutrinos are the most abundant matter particle in the universe, and yet our knowledge of them is still lacking in fundamental respects. We do not know whether neutrinos and anti-neutrinos are really distinct particles, or just different versions of the same underlying particle, which is possible since they do not carry any charge. In recent decades neutrino oscillation experiments have shed considerable light on the flavour structure of neutrinos, and in particular how neutrinos may turn from one flavour into another due totheir tiny mass differences. However, despite knowing rather precisely these mass differences, we still do not know what the absolute mass scale of theneutrino is. One of the highest priorities in particle physics today is to elucidate some of these mysteries surrounding the neutrino. This maygive us further insight into such fundamental questions as the nature ofphysics at the extremely high energies associated with Grand Unification,and the source of the matter-antimatter asymmetry which we observe in theuniverse today.Beta decay is a familiar radioactive process whereby a parent nucleusdecays into a daughter nucleus with the emission of an electron andan (unseen) anti-neutrino. In certain nuclei beta decay is forbidden but,very rarely, two simultaneous beta decays may occur. The distinctivesignature of two electrons being emitted has been observed in severalisotopes. We are searching for a distinct form of double-beta decayin which no neutrinos are emitted alongside the electrons, resulting inthe electrons carrying away the full energy of the associated nucleardecay. This "neutrinoless" process can only occur if neutrinos and anti-neutrinos are the same fundamental particle. Moreover, by measuring the rate of such decays we can effectively measure the absolute mass of the neutrino.In order to search for neutrinoless double-beta decay with greatersensitivity then ever before, we have built what is essentially the largest Geiger counter in the world. This so-called "tracker" for the SuperNEMO experiment records ionisation left by the electrons from the double-beta decay and allows us to visualise the tracks that they leavein the detector. UK groups have been building this tracking detectorfor the last 3 years, based on extensive R&D that took place before that.The next phase for SuperNEMO is to take the UK-built tracker to anunderground laboratory located under the Alps between France and Italyin order to shield the experiment from cosmic rays. There, we will marry the tracker with the other components of the detector that are being assembled by colleagues in France, Russia, the Czech Republic andthe US. Extensive work will be required to carefully assemble thefirst module of SuperNEMO, called the "Demonstrator Module", such thatit works as expected and that no radioactive contamination is allowed to enter the detector. Even trace contamination, far below the level of radioactivityin ordinary materials, could completely swamp the very rare processes thatwe are searching for.By the end of this project, the SuperNEMO Demonstrator Module will beup and running and launching into an exciting physics program to tryto address some of the fundamental questions outlined above.