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

暗物质的存在是从引力效应中得知的，但它的性质仍然是一个谜。在基本粒子物理学的其他考虑所激发的一种可能性是暗物质由未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。构成弥漫星系的暗物质晕的WIMP的轨道运动应该会导致WIMP与核的碰撞，其能量足以被敏感的实验室仪器观测到。该奖项将为研究和开发步骤提供资金，以支持DarkSide-G2，这是第二代（“G2”）直接WIMP搜索，使用有效质量为3.3吨的液态氩时间投影室（TPC）。液态氩是一种很有前途的WIMP探测介质，因为它可以有效地将WIMP引起的核反冲能量转化为电离和闪烁能量。氩闪烁时间曲线（“脉冲形状”）取决于电离粒子的类型，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，当与电离测量相结合时，背景抑制甚至进一步增强。如果使用大气氩，则吨级或更大的液态氩TPC的性能将受到39-Ar β衰变的高速率的限制。DarkSide-G2将使用从地下来源收集的氩气，这些氩气的39-Ar含量至少比大气中的氩气低150倍。这些资金将使这些小组能够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，并开发和确定最大限度地提高实验灵敏度所需的极放射纯探测器组件和技术。这项活动将以各种方式促进天体粒子物理学的发展及其科学和教育使命：（1）它将为学生的培训提供一个持续的机会，他们将有机会为基础科学和先进工程的尖端项目做出贡献;（2）通过开发可应用于从国家安全到医学成像等领域的技术，造福社会;以及（3）它将支持继续发展成功的教育&和职业发展项目，如LNGS-South Dakota-Princeton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.