SuperNEMO Commissioning and Sensitivity Demonstration

中微子是宇宙中最丰富的物质粒子，但我们对中微子的基础知识仍然缺乏。我们不知道中微子和反中微子是否真的是不同的粒子，或者只是同一个底层粒子的不同版本，这是可能的，因为它们不携带任何电荷。近几十年来，中微子振荡实验对中微子的味道结构有了相当大的了解，特别是中微子如何由于微小的质量差异而从一种味道变成另一种味道。然而，尽管我们相当准确地知道了这些质量差异，我们仍然不知道中微子的绝对质量尺度是多少。当今粒子物理学的首要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深入了解与大统一相关的极高能量下的物理学本质，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。β衰变是一种熟悉的辐射过程，通过发射电子和(看不见的)反中微子，母核衰变成子核。在某些原子核中，β衰变是被禁止的，但极少数情况下，可能会同时发生两个β衰变。在几种同位素中观察到了发射的两个电子的明显特征。我们正在寻找一种独特的双β衰变，在这种衰变中，没有中微子与电子一起发射，导致电子带走相关核衰变的全部能量。只有在中微子和反中微子是同一基本粒子的情况下，才会发生这种“无中微子”的过程。此外，通过测量这种衰变的速度，我们可以有效地测量中微子的绝对质量。为了寻找比以往任何时候都更灵敏的无中微子双β衰变，我们建造了基本上是世界上最大的盖革计数器。超NEMO实验的这个所谓的“跟踪器”记录了双β衰变过程中电子留下的电离，并允许我们可视化它们在探测器中留下的轨迹。在过去的三年里，英国团队一直在大量研发的基础上建造这种跟踪探测器。SuperNEMO的下一阶段是将英国制造的跟踪器带到法国和意大利之间阿尔卑斯山下的一个地下实验室，以保护实验免受宇宙射线的伤害。在那里，我们将把追踪器与探测器的其他部件结合起来，这些部件是由法国、俄罗斯、捷克和美国的同事组装的。将需要大量的工作来仔细组装超近地电磁探测器的第一个模块，称为“演示模块”，这样它就像预期的那样工作，并且不允许任何放射性污染进入探测器。即使是微量的污染，远远低于普通材料中的放射性水平，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，SuperNEMO演示模块将启动并运行，并启动一个令人兴奋的物理计划，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.