Collaborative Research: R & D Toward DarkSide-G2, a Second-Generation Direct Search for Dark Matter

暗物质的存在是通过引力效应得知的，但它的性质仍然是一个深层次的谜团。在基本粒子物理学其他考虑因素的推动下，一种可能性是暗物质由未被发现的基本粒子组成；弱相互作用大质量粒子(WIMP)是一种可能性。WIMP可能构成暗物质的证据可能来自欧洲核子研究中心大型强子对撞机的实验，或者来自探测星系晕中WIMP-WIMP湮灭产生的辐射的灵敏天文仪器。组成遍布银河系的暗物质晕的WIMP的轨道运动应该会导致足够能量的WIMP-核碰撞，从而可以用灵敏的实验室设备观察到。这项奖励将为支持Darkside-G2的研究和开发步骤提供资金，Darkside-G2是使用有效质量为3.3吨的液态Ar时间投影室(TPC)进行的第二代(“G2”)直接WIMP搜索。液态Ar能有效地将WIMP引起的核反冲能量转化为电离和闪烁能量，是一种很有前途的WIMP探测介质。Ar闪烁时间分布(“脉冲形状”)取决于电离粒子的类型，从而提供可用于抑制背景的粒子辨别。这是所有暗物质探测器中最强大的背景抑制因素之一，与电离测量相结合，背景抑制作用进一步增强。如果使用大气中的Ar，吨级或更大规模的液态Ar TPC的性能将受到39-Arβ衰减率高的限制。Darkside-G2将使用从地下来源收集的Ar，已证明其39-Ar含量至少比大气Ar低150倍。这些资金将允许这些小组进行必要的详细机械设计工作，以确保探测器的功能，开发必要的高压和数据采集元件，并开发和确定使实验的灵敏度最大化所需的极端放射性探测器组件和技术。广泛影响：这项活动将以各种方式推动天体粒子物理学的发展及其科学和教育任务：(1)它将为学生提供持续的培训机会，他们将有机会在基础科学和先进工程方面贡献尖端项目；(2)它将通过开发可应用于从国家安全到医学成像等领域的技术来造福社会；(3)它将支持继续发展成功的E&A；O项目，如LNGS-南达科他州-普林斯顿高中生暑期学校。

The existence of dark matter is known from gravitational effects, but its nature remains a deep mystery. One possibility motivated by other considerations in elementary particle physics is that dark matter consists of undiscovered elementary particles; Weakly Interacting Massive Particles (WIMPs) are one possibility. Evidence for WIMPs that could constitute dark matter may come from experiments at the Large Hadron Collider at CERN or from sensitive astronomical instruments that detect radiation produced by WIMP-WIMP annihilations in galaxy halos. The orbital motion of the WIMPs composing the dark matter halo pervading the galaxy should result in WIMP-nuclear collisions of sufficient energy to be observable by sensitive laboratory apparatus. This award will provide funding for research and development steps to support DarkSide-G2, a second-generation ("G2") direct WIMP search using a liquid argon Time Projection Chamber (TPC) with an active mass of 3.3 tons. Liquid argon is a promising medium for WIMP detection due to its efficient conversion of energy from WIMP-induced nuclear recoils into both ionization and scintillation. The argon scintillation time profile ("pulse shape") depends on the type of ionizing particle, providing particle discrimination that can be used to suppress background. This is one of the most powerful background rejection factors among all dark matter detectors, and when combined with the measurement of ionization, background rejection is even further enhanced. The performance of a ton-scale or larger liquid argon TPC would be limited by the high rate of 39-Ar beta decays if atmospheric argon was used. DarkSide-G2 will use argon collected from underground sources which has been shown to have 39-Ar content lower than atmospheric argon by at least a factor of 150. These funds will allow the groups to carry out the detailed mechanical design work necessary to ensure the functionality of the detector, develop necessary high voltage and data acquisition elements, and develop and identify the extremely radiopure detector components and techniques necessary to maximize the sensitivity of the experiment.Broader impacts: This activity will advance the development of astroparticle physics and its scientific and educational mission in a variety of ways: (1) it will offer a continuing opportunity for the training of students, who will have a chance to contribute a cutting-edge project in fundamental science and advanced engineering; (2) it will benefit society by developing techniques that could find application in areas ranging from national security to medical imaging; and (3) it will support continued development of successful E&O programs such as the LNGS-South Dakota-Princeton summer school for high school students.