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: 2014
• 资助国家: 加拿大
• 起止时间: 2014-01-01 至 2015-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=568027
• 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）是一个长期、低成本、高寿命和低维护的专用超新星探测器，在SNOLAB运行。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HALO对电子中微子具有独特的敏感性，并将提供下一个银河系超新星中微子通量和能量的补充信息。HALO还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系超新星警报的可能性。II型超新星是由大质量星星核心引力坍缩释放的能量提供动力的。最初非常热的原中子星星冷却主要是通过中微子的发射，所有的味道平均分配，在几十秒内。事实上，大约99%的引力势能是在~10MeV中微子的急剧爆发中释放的。从概念上讲，HALO是一个80吨重的铅，装有氦-3中子探测器。在HALO中，来自超新星的高能和强中微子脉冲可以通过带电电流（CC）和中性电流（NC）的弱相互作用激发铅核，使其处于一个或两个中子被射出的状态。随后在HALO的氦-3中子探测器中探测到这些中子，这标志着一颗银河系超新星的诞生。直接测量的时间演化的光度，味分区和平均中微子能量是我们唯一的直接窗口超新星动力学虽然引力波也是预期的。铅的核物理学对电子中微子通量的CC相互作用提供了占主导地位的敏感性;对电子反中微子通量的CC相互作用完全不敏感;以及对通过NC激发通道的所有味道的轻微敏感性。对超新星动力学的详细了解是大规模计算物理学工作的最前沿，当与观测数据相结合时，提供了提取基本中微子性质的可能性，以及推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是这样的，质量在100吨到100千吨之间的探测器只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为每世纪约3次，这就强调了用尽可能多的具有不同特性和灵敏度的探测器捕捉下一次此类事件的重要性。从SN 1987A观测到的20个事件中，我们学到了很多东西。下一个银河系超新星和当前一代的探测器应该有更多的可能，但是这些探测器大多数都是高成本，高维护，主要针对其他物理目标，并且由于延长校准运行，维修，重大修改等而受到可观的停机时间，因此可能相对较短。通过采用强大的中子探测技术，注重细节，并通过回收可用的设备和材料，HALO实现了其作为长寿命，低成本和低维护超新星探测器的目标。自2012年5月8日以来，HALO一直在一种模式下运行，其中完全填充了氦-3探测器，这些探测器几乎连续读出。虽然还有一些重要的工作要做，但为了完成并全面投入使用HALO，该合作希望在ORNL Spinning中子源测量中微子-铅横截面的可能性方面投入一些努力，并研究可能适用于大型铅基超新星探测器的技术。