Dark matter searches with LZ detector and their interpretation using Effective Field theory

使用 LZ 探测器搜索暗物质并使用有效场理论对其进行解释

• 批准号: 2113040
• 金额: --
• 依托单位: University of Liverpool
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2018
• 资助国家: 英国
• 起止时间: 2018 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2113040
• 关键词: Dark; matter; searches; LZ; detector

It is well understood that the abundance of visible matter in the universe is not sufficientto explain observed cosmological phenomena. Examples of this include: the rotationalvelocity distribution of matter within a galaxy, interactions between galaxy clusters, andgravitational lensing where there is insufficient luminous matter to do so. It has been postulatedthat there is matter within the universe that does not interact via the electromagneticforce and as a result is 'transparent'. This is collectively referred to as dark matter.Current astrophysical models calculate the energy in the universe to be 5 % baryonicmatter, 26 % dark matter, and roughly 69% dark energy [1]. Therefore, over 80% of thematter in the universe does not interact via the electromagnetic force. Models of physicsbeyond the standard model, such as supersymmetry, predict massive particles that only interactvia forces weaker than electromagnetism [2]. Collectively these particles are referredto as WIMP (weakly interacting massive particle) like. It is therefore predicted that WIMPparticles can interact with atomic nuclei, resulting in a nuclear recoil. This signal should bedirectly detectable by a sufficiently sensitive detector [3].The direct detection of dark matter on earth depends on the local properties of the MilkyWay's dark matter halo. These properties include the dark matter mass density, which isdirectly related to the WIMP-nucleon cross section. The field of direct dark matter detectionis wide and highly competitive, but detectors such as LUX and Xenon100 which measure theWIMP xenon cross-section are of particular relevance to this PhD project. These detectorsconsist of a liquid xenon time projection chamber (TPC) used to measure the intensity ofS1 and S2 signals. In a dual-phase xenon TPC, S1 refers to the light produced by promptscintillation after an interaction and S2 refers to the electroluminescence produced by driftelectrons during a phase transition. The ratio of these two signals can be used to distinguishbetween unwanted background and genuine WIMP interactions.The University of Liverpool is a collaborator in the LUX-Zeplin (LZ) experiment whichis due to be fully operational by 2021. Currently under construction, it is the largest everliquid xenon TPC, designed to operate with a fully active 7 tonnes of liquid xenon [3]. Thislarge increase in fiducial volume will give LZ the ability to detect interactions with crosssections2-3 orders of magnitude lower than LUX.The LZ group at Liverpool are all members of the Outer Detector (OD) physics group.The LZ OD will surround the TPC in 2 layers, these are simultaneously observed by 120Hamamatsu R5912 photomultiplier tubes and act as a veto [3]. The first layer consists of17.5 tonnes of gadolinium-loaded liquid scintillator, the second consists of 228 tonnes ofwater. The liquid scintillator is doped with gadolinium because it has a high neutron capturecross-section. Neutrons interacting in the TPC have a WIMP like signature and it istherefore essential that they are successfully vetoed. The water surrounding the scintillatoracts as an effective shielding material by thermalising neutrons and absorbing backgroundradiation from the surrounding rock. It can also act as a cherenkov detector for high energybackground such as cosmic ray muons and the daughter particles produced by their interactions.The primary responsibility of the Liverpool group is the production of an Optical CalibrationSystem. This system has been specified to produce a known quantity and wavelengthof optical photons in a well documented spectrum. This will allow the group to continuouslycalibrate the 120 PMTs surrounding the OD and verify the system's stability. It alsoallows for the validation of the optical model of the materials and geometry of the OD bycomparison to simulated events. My hardware responsibility during my PhD project will

众所周知，宇宙中可见物质的丰度并不足以解释观测到的宇宙学现象。这方面的例子包括：星系内物质的旋转速度分布，星系团之间的相互作用，以及没有足够发光物质的引力透镜。它被假定为宇宙中存在着不通过电磁力相互作用的物质，因此是“不相干的”。目前的天体物理学模型计算出宇宙中的能量是5%的重子物质，26%的暗物质和大约69%的暗能量[1]。因此，宇宙中超过80%的物质不通过电磁力相互作用。超越标准模型的物理模型，如超对称性，预测大质量粒子只能通过比电磁力弱的力相互作用[2]。总的来说，这些粒子被称为WIMP（弱相互作用大质量粒子）。因此，预测WIMP粒子可以与原子核相互作用，导致核反冲。这个信号应该可以被足够灵敏的探测器直接探测到[3]。对地球上暗物质的直接探测取决于银河之路暗物质晕的局部性质。这些性质包括暗物质的质量密度，它与WIMP-核子截面直接相关。直接暗物质探测的领域很广，竞争也很激烈，但是像LUX和Xenon 100这样测量WIMP氙截面的探测器与这个博士项目特别相关。这些探测器由一个液体氙时间投影室（TPC）组成，用于测量S1和S2信号的强度。在双相氙TPC中，S1是指相互作用后由氙闪烁产生的光，S2是指在相变期间由漂移电子产生的电致发光。这两个信号的比例可以用来区分不需要的背景和真正的WIMP相互作用。利物浦大学是LUX-Zeplin（LZ）实验的合作者，该实验将于2021年全面投入使用。目前正在建设中，它是最大的永远液体氙气TPC，设计用于完全活跃的7吨液体氙气[3]。基准体积的大幅增加将使LZ能够检测比LUX低2 -3个数量级的截面的相互作用。利物浦的LZ组都是外部检测器（OD）物理组的成员。LZ OD将以2层包围TPC，这些层由120个Hamamatsu R5912光电倍增管同时观察并作为否决[3]。第一层由17.5吨钆液体闪烁体组成，第二层由228吨水组成。液体闪烁体掺杂有钆，因为它具有高的中子俘获截面。在TPC中相互作用的中子具有类似于WIMP的特征，因此成功地否决它们是至关重要的。围绕在中子发生器周围的水通过热化中子和吸收来自周围岩石的反向辐射而起到有效的屏蔽材料的作用。它也可以作为一个切伦科夫探测器的高能背景，如宇宙线μ子和他们的相互作用产生的子粒子。利物浦组的主要责任是生产的光学校准系统。该系统已被指定为在有据可查的光谱中产生已知数量和波长的可见光子。这将使小组能够持续校准OD周围的120个PMT，并验证系统的稳定性。它还允许通过与模拟事件进行比较来验证材料的光学模型和OD的几何形状。我在博士项目期间的硬件责任将