Background Characterisation for the Water and Scintillator Phases of SNOPLUS

简介SNO+是一项跨国合作，致力于探测被称为无中微子双β衰变的放射性衰变过程。该实验是在安大略省萨德伯里的Creighton镍矿进行的，并建立在之前在SNO探测器上进行的工作的基础上(SNO+实验的全面概述见[1])。实验动机观察无中微子双β衰变的主要目的是测试超越标准模型的物理。如果观察到这种衰变过程，将证明中微子实际上是Majorana费米子，即它们是自己的反粒子。因此，这将导致轻子数守恒被打破，并将对瘦子发生的机制产生更广泛的影响。此外，如果中微子是Majorana粒子，这将使人们能够确定中微子的质量等级，并计算三种中微子类型的绝对质量。由于探测器的灵敏度，SnO+可能不会完全限制Majorana中微子的质量。然而，它将有能力将这个有效质量的上限设置在55-133 MeV之间。SNO+还将能够在其运行期间进行其他物理研究。在实验期间，探测器将对高能太阳中微子、超新星中微子和看不见的核子衰变敏感。此外，SNO+将能够在特定阶段探测到低能量的太阳能、反应堆和地中微子。实验背景SnO+探测器在其生命周期中将有3个不同的阶段。最初，SNO+用作水切伦科夫探测器，填充了大约900吨超纯水(UPW)。在第二阶段，探测器将充满液体闪烁体(LS)，使探测器对反中微子相互作用敏感。最后，将碲酸加载到闪烁体中，开始最后的阶段。博士研究背景本博士期间开展的研究将主要集中在探测器内放射性本底的表征和监测。氡同位素作为通过子体同位素放射性衰变进行的几项研究的背景；这一点特别重要，因为矿井空气中的氡含量很高。太阳中微子和核子衰变的研究很容易受到这些背景的影响(在水相期间)，以及反应堆、地球中微子和无中微子双β衰变研究(在LS和Te加载阶段)。在处理探测器数据后，将使用识别铋214衰变的技术来表征切伦科夫阶段的氡背景。此外，将开发一种识别阿尔法中子反应的瞬时延迟辨别技术，以抑制钚210引起的本底信号。由于探测器充满了闪烁体，这项技术将在探测器的第二和第三阶段进行测试、改进并用于分析这一背景。还将在探测器现场花费时间，以帮助探测器进入LS阶段。在此期间，将为准备和组装探测器硬件做出贡献。这将侧重于安装脐带回收机制(用于部署校准源)。此外，将进行调查，以优化将部署在闪烁器内的脐带的清洁技术。参考文献。Andringa等，《SNO+实验的现状和未来展望》，《高能物理进展》，2016卷，第1-21页，2016。提供时间：10.1155/2016/6194250[19/15/11]。

Introduction SNO+ is a multinational collaboration working on the detection of the radioactive decay process known as the neutrinoless double beta decay. The experiment is based at the Creighton nickel mine in Sudbury, Ontario and builds upon previous work carried out at the location on the SNO detector (a comprehensive overview of the SNO+ experiment is available at [1]). Experimental Motivations The principal aim, of observing the neutrinoless double beta decay, is to test for physics beyond the Standard Model. If this decay process is observed, it will demonstrate that neutrinos are in fact Majorana fermions i.e. that they are their own anti-particles. This would therefore result in lepton number conservation being broken and would have wider reaching implications for mechanisms of leptogenesis.Furthermore, if neutrinos are Majorana particles, this would enable one to identify the neutrino mass hierarchy and calculate the absolute mass of the 3 neutrino types. SNO+ may not completely constrain the Majorana neutrino mass due to the detector's sensitivity. However, it will have the ability to set an upper limit of between 55 - 133 meV on this effective mass.SNO+ will also be able to conduct other physical studies during its operation. The detector will be sensitive to high energy solar neutrinos, supernovae neutrinos and invisible nucleon decays for the duration of the experiment. Moreover, SNO+ will be able to detect low-energy solar, reactor and geoneutrinos during specific phases. Experimental Context The SNO+ detector will have 3 distinct phases during its lifetime. Initially, SNO+ functioned as a water Cherenkov detector and was filled with approximately 900 tonnes of Ultra Pure Water (UPW). During the second phase, the detector will be filled with liquid scintillator (LS) making the detector sensitive to antineutrino interactions. Finally, Telluric acid will be loaded into the scintillator to begin the final phase. Context of PhD ResearchThe research carried out during this PhD will predominantly focus on the characterisation and monitoring of radioactive backgrounds within the detector. Radon isotopes act as a background to several of the studies through the radioactive decays of daughter isotopes; this is of particular importance due to the high presence of radon in the mine air. Solar neutrino and nucleon decay studies are susceptible to these backgrounds (during the water phase) as well as reactor, geoneutrino and neutrinoless double beta decay studies (during the LS and Tellurium loaded stages).Techniques to identify bismuth 214 decays will be employed to characterise radon backgrounds during the Cherenkov phase following the processing of the detector data. Furthermore, a prompt-delay discrimination technique to identify alpha-neutron reactions will be developed to supress the background signal caused by polonium 210. As the detector is filled with scintillator, this technique will be tested, enhanced and employed to analyse this background during the second and third detector phases.Time will also be spent at the detector site to aid in advancing the detector into the LS stage. During this time, contributions will be made to preparing and assembling detector hardware. This will focus on the installation of an umbilical retrieval mechanism (for the deployment of calibration sources). Furthermore, investigations will be preformed to optimise cleaning techniques for the umbilicals that will deployed within the scintillator. ReferenceS. Andringa et al., "Current Status and Future Prospects of the SNO+ Experiment", Advances in High Energy Physics, vol. 2016, pp. 1-21, 2016. Available: 10.1155/2016/6194250 [Accessed 15/11/19].