Search for Dark Matter with PICO (PICASSO/COUPP)

寻找宇宙中神秘的失踪质量已经成为当今粒子物理学和宇宙学的重大挑战之一。天文观测表明，宇宙中只有1%的物质是发光的，现在有令人信服的证据表明，宇宙中85%的引力可追踪物质是一种新的奇异物质，不同于我们周围的质子，中子和电子的“普通”物质。这种所谓的冷暗物质（CDM）被认为是由所谓的WIMP（弱相互作用大质量粒子），中性粒子组成，比质子重10到1000倍，彼此之间和普通物质之间的相互作用非常弱。 PICASSO* 暗物质实验被调整为寻找WIMP。它是基于液体到蒸汽的相变，这可以引起的WIMP与亚稳态过热液滴中的核相互作用。在目前阶段，PICASSO合作项目在加拿大安大略萨德伯里的SNOLAB地下实验室安装了32个探测器，目标总质量为2.6公斤。并且是连续获取的数据。2012年发表的结果将PICASSO置于直接自旋相关暗物质搜索的最前沿。对整套探测器的新的物理分析目前已经完成，预计将比我们2012年的结果有很大改进。新的分析还扩展到自旋独立部门，新的PICASSO数据开始探测联合CoGENT/DAMA/CRESST年度调制区域。 由毕加索发现的过热液体技术的强大的背景鉴别特征保证了对高达吨年暴露的“背景盲”操作。因此，2012年12月，过热液体领域的两个领先团队PICASSO和COUPP在新的皮科合作中联合起来，共同致力于在SNOLAB进行500 kg暗物质实验。在250 L气泡室中，过热的C4 F10或C3 F8作为活性靶，皮科-250 L将专注于自旋相关的质子相互作用，预期灵敏度为3 x 10-7 pb，可进行一年的实时数据采集。在自旋无关的扇区中，对于质量约为20 GeVc-2的WIMP，灵敏度达到约4 x 10-10 pb，灵敏度增加到几个GeVc-2的质量。 皮科-250 L符合下一代暗物质实验（G2）的定义，没有其他G2实验在自旋相关相互作用和轻WIMP质量方面具有可比的灵敏度。目前，背景源似乎得到了很好的控制;皮科500的工程设计进展顺利。14/ 15财政年度的工作将集中在施工上，预计15/16财政年度将进行调试。 加拿大PICASSO /皮科小组由五个机构的研究小组组成：阿尔伯塔大学、劳伦蒂安大学、蒙特利尔大学、女王大学和多伦多大学。在本资助申请中，我们要求提供运营资金，以完成PICASSO的现阶段工作，该阶段工作应于2013年夏季结束，并要求提供运营资金，以支持我们在皮科-250 L中的工作。*Project In Canada to Search for Supersymmetric Objects加拿大搜寻超对称天体项目

The quest for the mysterious missing mass of the Universe has become one of the big challenges for today's particle physics and cosmology. Astronomical observations show that only 1% of the matter of the Universe is luminous and there is now convincing evidence that 85% of all gravitationally traceable matter in the Universe is of a new exotic kind, different from the "ordinary" matter surrounding us with its protons, neutrons and electrons. This so-called Cold Dark Matter (CDM) is thought to consist of so-called WIMPs (Weakly Interacting Massive Particles), neutral particles, about ten to thousand times heavier than a proton and which interact extremely weakly with each other and ordinary matter. The PICASSO* dark matter experiment is tuned to the search for WIMPs. It is based on liquid-to-vapour phase transitions which can be induced by WIMP interactions with nuclei in metastable superheated droplets. In its present phase the PICASSO collaboration has installed 32 detectors with a total target mass of 2.6 kg data in the SNOLAB underground laboratory at Sudbury, Ontario, Canada. and is continuously taken data. Results published in 2012 had placed PICASSO at the forefront of direct spin-dependent dark matter searches. A new physics analysis of an entire set of detectors is presently finalized and a substantial improvement with respect to our 2012 results is anticipated. The new analysis extends also to the spin-independent sector where the new PICASSO data start to probe the joint CoGENT/DAMA/CRESST annual modulation region. The powerful background discrimination features of the superheated liquid technique discovered by PICASSO promise “background blind” operation for up to tonne - year exposures. Therefore in December 2012 the two leading groups in the field of superheated liquids, PICASSO and COUPP joint forces within the new PICO collaboration to work together towards a 500 kg dark matter experiment at SNOLAB. With superheated C4F10 or C3F8 as the active target in a 250L bubble chamber, PICO-250L would focus on spin-dependent proton interactions, with an expected sensitivity at the level of 3 x 10-7 pb for one year of live data taking. In the spin-independent sector the sensitivity reach would be around 4 x 10-10 pb for WIMP masses around 20 GeVc-2, with an increased sensitivity down to masses of a few GeVc-2. PICO-250L meets the definition of a next generation dark matter experiment (G2) and no other G2 experiment would have comparable sensitivities in the sectors of spin-dependent interactions and light WIMP masses. At the moment background sources appear well under control; the engineering design of PICO 500 is progressing well. Work during FY14 / 15 will concentrate on construction, with commissioning foreseen in FY15/16. The Canadian PICASSO / PICO contingent consists of research groups of five institutions: University of Alberta, Laurentian University, Université de Montréal, Queen’s University and University of Toronto. In this grant request we ask for operating funds for the completion of the present phase of PICASSO, which should be concluded by summer 2013, and for operating funds to support our work in PICO-250L. *Project In Canada to Search for Supersymmetric Objects Projet d'Identification de CAnditats Supersymetriques Sombres