Distinguishing Dark Matter Signals from Neutron Backgrounds

暗物质的本质是物理学中最大的谜团之一。暗物质的直接信号仍然难以捉摸。随着未来的搜索向更高的灵敏度和更小的相互作用截面推进，背景，尤其是中子的背景，必然会出现。通过更大的地下深度和更多的屏蔽将这些背景降低到可以忽略不计的水平，对于非常大的探测器来说是不切实际的。因此，当我们接近在深地下科学与工程实验室进行暗物质搜索的时候，我们很可能不得不离开零背景范式，而是在一个很好理解的中子背景之上搜索信号。这个问题需要一种新的暗物质搜索方法。该奖项的研究目标是利用SNOLab地下的液态氩（LAr）暗物质探测器（MiniCLEAN）在已知中子背景之上寻找暗物质信号。本研究的目标是：(i)利用40-Ar上的多重散射、非弹性散射和中子俘获，建立原位测量ar暗物质探测器中子背景的方法；（ii）开发围绕暗物质探测器的主动中子否决；（三）应用统计工具结合这些中子背景测量，在暗物质搜索中寻找背景以上的信号。MiniCLEAN的设计是暗物质搜索的新方向。它利用非常成功的、经过验证的太阳中微子物理学方法来建造低背景探测器，这种探测器可以简单地测量数吨重的目标。MiniCLEAN对暗物质的这种方法的成功演示将为未来的超大型探测器开辟新天地。成功主要取决于背景抑制；解决困难的中子组件是本提案的重点。更广泛的影响：使用这些新方法测量中子通量将为设计未来的大型暗物质探测器提供及时的输入，并为其他低背景实验提供屏蔽，包括无中微子双β衰变和低能太阳中微子实验。

The nature of dark matter is one of the great mysteries in physics. Direct signals for dark matter have remained elusive. As future searches push to greater sensitivities and smaller interaction cross sections, backgrounds, especially from neutrons, will necessarily arise. Reducing these backgrounds to a negligible level through greater underground depths and more shielding will become impractical for very large detectors. Thus, as we move toward the time when dark matter searches will be performed at the Deep Underground Science and Engineering Laboratory, it is likely that we may have to depart from the zero-background paradigm, instead searching for signals above a well understood neutron background. This problem calls for a new approach to dark matter searches. The research objective of this award is a search for a dark matter signal above a well understood neutron background, using a liquid Argon (LAr) dark matter detector (MiniCLEAN) underground in SNOLab. The goals of this research are: (i) to develop methods for measuring the neutron background in-situ in LAr dark matter detectors using multiple scattering, inelastic scattering, and neutron capture on 40-Ar; (ii) to develop an active neutron veto surrounding the dark matter detector; and (iii) to apply statistical tools incorporating these neutron background measurements in a dark matter search for signal above background. The MiniCLEAN design is a new direction for dark matter searches. It draws on highly successful, proven approaches of solar neutrino physics to building low-background detectors that scale simply to multi-tonne targets. Successful demonstration of this approach for dark matter by MiniCLEAN will break new ground for future, very large detectors. Success depends critically on background suppression; addressing the difficult neutron component is the focus of this proposal.Broader impacts: Measurements of the neutron flux using these new methods will provide timely input to designing future large dark matter detectors, as well as shielding for other low background experiments, including neutrino-less double beta decay and low-energy solar neutrino experiments.