Grant: Subatomic Physics Envelope - Research Tools and Instruments

The HALO detector at SNOLAB has been designed to be a long-lifetime, low-maintenance dedicated supernova neutrino detector. It is also a detector of opportunity in the sense that it has been constructed largely from recycled materials made available to the HALO collaboration by previous experiments. In particular, the availability of 79 tonnes of lead blocks from a decommissioned cosmic ray station; an array of the world's lowest-radioactivity Helium-3 neutron detectors, originally built for the SNO experiment; and readout electronics also from the SNO experiment, has permitted the construction of HALO for a very modest public investment. Supernovae are cataclysmic events that occur at the end of the life cycle of a massive star. Core-collapse supernovae are characterized by the fleeting emission of astronomical numbers of neutrinos. Just as we have used neutrinos to look into the core of the sun, and to confirm that it is powered by nuclear fusion, we can, by detecting the energetic neutrinos from a supernova explosion, look into an exploding star anywhere within our galaxy. The detailed understanding of all the physical laws that govern what happens during a supernova is currently one of the grand challenges of computational physics. Intrinsically, supernovae are of fundamental importance and interest due to the fact that they are the site for the creation of the heavy elements, and that they are responsible for the dispersion of these elements within the galaxy. The detection of supernova neutrinos offers the possibility of advancing our knowledge by providing data against which computational models can be tested. There is a great potential to learn things both about the supernova process as well about the nature and interactions of neutrinos by making such a comparison. HALO detects supernova neutrinos by using lead as a target. Energetic neutrinos eject neutrons from the lead nuclei which are then captured by HALO's Helium-3 neutron detectors. On May 8th 2012 the HALO detector was fully operated for the first time. Since then it has been in near-continuous operation through a commissioning phase. We look forward in the very near future to joining the world-wide Supernova Early Warning System (SNEWS) which, since neutrinos escape an exploding star before the explosion itself actually reaches the surface of the star, permits neutrino detectors to inform astronomers of an impending supernova up to 10 hours before it is visible. HALO, in contrast to other supernova detector technologies, such as water Cherenkov and liquid scintillator detectors, is primarily sensitive to electron neutrinos, rather than electron anti-neutrinos, giving HALO a unique potential to contribute to the physics that will result from the next galactic supernova. Since galactic core-collapse supernovae are rare events occurring only a few times per century, and since they are also brief events with neutrino emission lasting less than a minute, HALO must strive for very high livetime to ensure its scientific impact. The initial electronics and data acquisition configuration of HALO, although operational and fully sensitive to a supernova in our galaxy, was created from the available SNO electronics, some of which was 20 years old. It did not have the redundancy and reliability needed to guarantee that HALO will remain live over the long anticipated life of the detector. Much progress has been made in working towards renewing critical components of the electronics, building in redundancy, and eliminating single points of failure. The only remaining detector element in need of renewal at this point is the High Voltage System. The objective of this grant application is close this gap and complete the electronics upgrade of HALO.