Search for Neutrinoless Double Beta Decay from the SNO+ Experiment

在过去十年里出现的一些最令人兴奋的物理学是在中微子物理学领域。这里最前沿的实验之一是萨德伯里中微子天文台(SNO)，总部设在加拿大安大略省萨德伯里的SNOLAB地下科学实验室，它是2015年诺贝尔物理学奖的获得者。牛津大学的SNO小组在解决“太阳中微子问题”方面发挥了主导作用，并首次清楚地证明了中微子以混合态的形式存在，这使得它们能够明显地从一种类型振荡到另一种类型。在这个极其成功的项目之后，一个后续的实验SNO+正在进行，它的物理目标非常多样化和有趣。这个项目的主要目标是灵敏地寻找一种非常罕见的过程，称为“无中微子双β衰变”。对此的观测既可以确定中微子的绝对质量，也可以确定中微子作为自己的反粒子，这可能会对我们理解宇宙中物质/反物质的不对称性产生重大影响。这一研究领域被认为在粒子物理学中具有极高的重要性，牛津小组在建立将用于这次搜索的技术方面发挥了基础性作用。此外，其他物理目标包括研究低能太阳中微子、反应堆反中微子的振荡、搜索核子衰变的非标准模式、研究地球内部产生的地球中微子，以及作为银河系超新星中微子的重要探测器。这名即将入学的学生将与牛津SNO+小组密切合作，该小组目前由3名学者、1名博士后研究员和4名其他博士后学生组成，是英国更大规模努力的一部分，该计划还包括另外4所机构：苏塞克斯大学、利物浦大学、KCL和兰开斯特大学。英国SNO+合作者约占合作项目的30%，并填补了项目中的许多关键职位，学生也将对此做出贡献。牛津大学小组的负责人史蒂夫·比勒是英国的发言人，并领导了无中微子双β衰变闪烁体中碲加载技术的开发工作，牛津大学在这方面做出了重大贡献，论文项目将涉及这项工作的延伸。这两个英国小组共同负责为该实验交付一个主要的校准系统，该系统的牛津部分专注于探测器内的光学散射的现场测量，学生的工作还将涉及与该系统相关的分析。这篇论文的主要物理工作将集中于产生关于无中微子双β衰变的主要结果。探测器目前正在经历从水到闪烁体填充的过渡，无中微子双β衰变的同位素将在未来两年内引入。即将入学的博士生将参与开发、模拟、校准、操作、分析和产生一些中心实验结果。

Some of the most exciting physics to emerge over the last decade has been in the field of neutrino physics. One of the forefront experiments here has been the Sudbury Neutrino Observatory (SNO), based in the SNOLAB underground scientific laboratory in Sudbury, Ontario (Canada), which was a recipient of the 2015 Nobel Prize in physics. The SNO group at Oxford have played a leading role in solving the "Solar Neutrino Problem" and clearly demonstrating, for the first time, that neutrinos exists as mixed states which allow them to apparently "oscillate" from one type to another. On the heels of this tremendously successful project, a follow-on experiment, SNO+, is being pursued with a remarkably diverse and interesting range of physics objectives. The main objective of this project is to sensitively search for a very rare process called "neutrinoless double beta decay." An observation of this would both permit a determination of the absolute neutrino masses and would establish that neutrinos act as their own antiparticles, which could have significant consequences for our understanding of the matter/antimatter asymmetry in the universe. This area of study is considered to be of extremely high importance in particle physics and the Oxford group has played a fundamental role in establishing the technique that will be used for this search. In addition, other physics goals include studies of low energy solar neutrinos, oscillations of reactor antineutrinos, searches for non-standard modes of nucleon decay, study of geo-neutrinos generated from within the earth, and to act as an important detector for neutrinos from galactic supernovae. The incoming student will work closely with the Oxford SNO+ group, which currently consists of 3 academics, 1 postdoctoral researcher and 4 other PhD students and is part of a larger UK effort, which includes 4 additional institutions: University of Sussex, University of Liverpool, KCL and University of Lancaster. The UK SNO+ collaborators comprise ~30% of the collaboration and fill many key positions within the project to which the student will also contribute. The head of the Oxford group, Steve Biller, is the UK spokesperson and leads the development effort on tellurium loading techniques in scintillator for neutrinoless double beta decay, where Oxford has made significant contributions and the thesis project will involve an extension of this work. The UK groups jointly have responsibility for delivering one of the major calibration systems for the experiment, the Oxford portion of which focuses on in situ measurements of optical scattering within the detector, and the student's work will also involve analysis related to this system. The main physics effort for the thesis will focus on producing the main results on neutrinoless double beta decay. The detector is currently undergoing the transition from water to scintillator fill and the isotope for neutrinoless double beta decay will be introduced over the next two years. The incoming PhD student will participate in development, simulation, calibration, operation, analysis and the production of some of the central experimental results.