Collaborative Research: Direct Search for Dark Matter with Underground Argon at LNGS

暗物质的存在是从引力效应中推断出来的，但它的本质仍然是一个深谜。根据基本粒子物理学的考虑，一种可能性是暗物质由假设的弱相互作用大质量粒子（wimp）组成。直接探测到wimp应该是可能的，因为构成星系暗物质晕的wimp的轨道运动应该会导致在实验室中可以观察到足够能量的wimp -核碰撞。这项合作利用资金来委托和运行DarkSide-50，这是一个使用有效质量为50公斤的液态氩时间投影室（LAr-TPC）的WIMP搜索。DarkSide-50将使用从地下来源提取的氩气（地下氩气，UAr），该小组已经证明，这些氩气的Ar-39含量至少比大气氩气低150倍。Ar-39是实验中主要的背景源之一。该小组研究的一个重要副产品是开发出可以在从国家安全到医学成像等领域找到应用的技术。这是由于从地下资源中提取稀有稀有气体（氩和氦）引起的，可能的应用包括探测地下核试验，以及在环境科学中，氩气被用作超低水平比例计数器测量的检测介质，用于水文运输的环境无线电示踪剂。液态氩能有效地将WIMP诱导的核反冲能量转化为电离和闪烁，是一种有吸引力的WIMP探测介质。氩闪烁时间分布（“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识别。氩气的脉冲形状判别是所有暗物质技术中最强大的背景抑制技术之一；当与电离测量相结合时，本底抑制进一步增强。拟议中的活动将通过以下方式促进天体粒子物理学及其科学和教育任务的发展：(1)为培训学生提供持续的良好机会，这些学生将有助于前沿项目的成功；(2)开发可以应用于几个对社会有益的领域的技术；(3)支持一项新的教育和推广计划，旨在接替非常成功的格兰萨索-南达科他州-普林斯顿国家实验室暑期学校。

The existence of dark matter is inferred from gravitational effects, but its nature remains a deep mystery. One possibility, motivated by considerations in elementary particle physics, is that dark matter consists of the hypothesized Weakly Interacting Massive Particles (WIMPs). It should be possible to detect WIMPs directly, as the orbital motion of the WIMPs composing the dark matter halo pervading the galaxy should result in WIMP-nucleus collisions of sufficient energy to be observable in the laboratory. This collaboration utilizes funds to commission and operate DarkSide-50, a WIMP search using a Liquid Argon Time Projection Chamber (LAr-TPC) with an active mass of 50 kg. DarkSide-50 will use argon extracted from underground sources (Underground Argon, UAr), which this group has shown to have an Ar-39 content lower, by at least a factor of 150, than atmospheric argon. Ar-39 is one of the main sources of background in the experiment.A significant by-product of this group's research has been developing techniques that could find application in areas ranging from national security to medical imaging. This arises from the extraction of rare noble gases (Argon and Helium) from underground sources, and possible applications include the detection of underground nuclear tests and in Environmental Science where Argon is used as a detection media in ultra-low level proportional counter measurements for an environmental radio tracer for hydrologic transport.Liquid argon is an attractive 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. Pulse shape discrimination in argon provides one of the most powerful background rejections among all dark matter technologies; when combined with the measurement of ionization, the background rejection is further enhanced. The proposed activity will advance the development of astroparticle physics and its scientific and educational mission by: (1) offering a continuing excellent opportunity for the training of students, who will contribute to the success of a cutting-edge project; (2) developing techniques that could find application in several areas of benefit to society; and (3) supporting a new education and outreach program, designed to succeed the highly successful Laboratori Nazionali del Gran Sasso-South Dakota-Princeton summer school.