HALO at SNOLAB

SNOLAB 的光环

• 批准号: SAPPJ-2014-00029
• 负责人: Virtue, Clarence
• 金额: $ 4.01万
• 依托单位: Laurentian University of Sudbury
• 依托单位国家: 加拿大
• 项目类别: Subatomic Physics Envelope - Project
• 财政年份: 2016
• 资助国家: 加拿大
• 起止时间: 2016-01-01 至 2017-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=612398
• 关键词: HALO; SNOLAB

The Helium and Lead Observatory (HALO) is a long-term, low cost, high livetime, and low maintenance dedicated supernova detector running at SNOLAB. Among the world’s supernova neutrino detectors the choice of lead as the target material makes HALO uniquely sensitive to electron neutrinos and will provide complementary information on neutrino fluxes and energies from the next galactic supernova. HALO will also participate in the SuperNova Early Warning System (SNEWS) increasing the odds that the astronomical community is promptly alerted to a galactic supernova. A type II supernova is powered by the energy liberated in the gravitational collapse of the core of a massive star. The initially very hot proto-neutron star cools primarily by the emission of neutrinos, of all flavours equally partitioned, in some tens of seconds. In fact, about 99% of the gravitational potential energy is released in a sharp burst of ~10MeV neutrinos. Conceptually, HALO is an 80 tonne mass of lead instrumented with Helium-3 neutron detectors. In HALO the energetic and intense pulse of neutrinos from a supernova can excite, via both charged current (CC) and neutral current (NC) weak interactions, the lead nuclei to states from which one or two neutrons are ejected. The subsequent detection of these neutrons in HALO’s Helium-3 neutron detectors signals a galactic supernova. The direct measurement of the time evolution of the luminosity, flavour partition, and average neutrino energy are our only direct window into supernova dynamics though a gravitational wave is also anticipated. The nuclear physics of lead provides for a dominant sensitivity to CC interactions of the electron neutrino flux; complete insensitivity to CC interactions of the electron anti-neutrino flux; and minor sensitivity to all flavours through NC excitation channels. A detailed understanding of supernova dynamics is at the forefront of large-scale computational physics efforts and, when combined with observational data, offers the possibility of extracting fundamental neutrino properties as well as advancing our understanding of the supernova mechanism, heavy element nucleosynthesis, and other astrophysical questions. Supernova neutrino fluxes and interaction cross-sections are such that detectors with masses between 100 tonnes and 100 kilotonnes are only sensitive to supernovae occurring in the Milky Way Galaxy. The rate of galactic supernovae is estimated at ~3 per century which underlines the importance of capturing the next such event with as many detectors of diverse characteristics and sensitivities as possible. A great deal was learnt from the 20 events observed from SN 1987A. Much more should be possible with the next galactic supernova and the current generation of detectors, however the majority of these detectors are high cost, high maintenance, primarily aimed at other physics objectives, and are subject to appreciable downtime due to extended calibration runs, repairs, major modifications, etc. and consequently may be relatively short-lived. By employing a robust technology for neutron detection, attention to detail, and by recycling available equipment and materials, HALO fulfills its objectives of a being a long lifetime, low cost and low maintenance supernova detector. Since May 8th 2012 HALO has been operating in a mode where it is fully populated with Helium-3 detectors with those detectors being read out nearly continuously. Although some important work remains, to complete and fully commission HALO, the collaboration wishes to invest some effort in the possibility of measuring neutrino-lead cross-sections at the ORNL Spallation Neutron Source, as well as to investigate technologies that may prove appropriate for larger-scale lead-based supernova detectors.

氦铅天文台 (HALO) 是在 SNOLAB 运行的长期、低成本、高寿命和低维护的专用超新星探测器，在世界上的超新星中微子探测器中，选择铅作为目标材料使得 HALO 对电子具有独特的敏感性。中微子，并将提供有关下一个银河超新星中微子通量和能量的补充信息，HALO也将参与超新星早期预警系统（SNEWS）。增加天文学界及时收到银河超新星警报的可能性。 II 型超新星由大质量恒星核心引力塌缩释放的能量提供动力，最初非常热的原中子星主要通过中微子的发射在几十秒内冷却。事实上，大约 99% 的重力势能是在约 10MeV 中微子的急剧爆发中释放的。从概念上讲，HALO 是一个 80 吨质量的中微子。在 HALO 中，来自超新星的高能和强烈的中微子脉冲可以通过带电电流 (CC) 和中性电流 (NC) 的弱相互作用，将引导核激发到其中一或两个状态。随后在 HALO 的 Helium-3 中子探测器中检测到这些中子，表明存在银河系超新星，直接测量光度的时间演化。味道分配和平均中微子能量是我们了解超新星动力学的唯一直接窗口，尽管铅的核物理也对电子中微子通量的 CC 相互作用提供了显着的敏感性，而对电子的 CC 相互作用完全不敏感。反中微子通量；以及通过数控激发通道对所有味道的轻微敏感性对超新星动力学的详细了解处于大规模计算物理工作的前沿，并且与观测数据相结合，提供了可能性。提取中微子的基本特性，并增进我们对超新星机制、重元素核合成和其他天体物理问题的理解。 超新星中微子通量和相互作用截面使得质量在 100 吨到 100 吨之间的探测器仅对银河系中发生的超新星敏感。银河系超新星的发生率估计约为每世纪 3 次，这强调了捕获超新星的重要性。我们从 SN 1987A 观测到的 20 个事件中学到了很多东西。下一代银河超新星和当前一代探测器应该有更多可能，但是这些探测器中的大多数成本高，维护成本高，主要针对其他物理目标，并且由于延长的校准运行、维修、重大修改等，因此可能相对短暂。 通过采用强大的中子探测技术、对细节的关注以及回收可用的设备和材料，HALO 实现了长寿命、低成本和低维护的超新星探测器的目标，自 2012 年 5 月 8 日起，HALO 一直在一个运行的超新星探测器中运行。模式中充满了 Helium-3 探测器，这些探测器几乎可以连续读取。尽管为了完成和全面调试 HALO，仍有一些重要的工作要做，但合作伙伴希望在测量的可能性上投入一些努力。橡树岭国家实验室散裂中子源的中微子铅横截面，以及研究可能证明适用于大型铅基超新星探测器的技术。