Grant: Subatomic Physics Envelope - Project

The Helium and Lead Observatory (HALO) is a low cost, high livetime, low maintenance supernova detector running at SNOLAB since May 2012. The use of lead as the target material gives HALO unique sensitivity to electron neutrinos, complementary to other detectors worldwide. HALO is a member of the SuperNova Early Warning System. Support is requested for the ongoing operation and maintenance of HALO. A type II supernova is powered by the gravitational collapse of the core of a massive star. The hot proto-neutron star cools primarily by the emission of neutrinos, of all flavours, in some tens of seconds. About 99% of the gravitational potential energy liberated emerges as ~10MeV neutrinos. Conceptually, HALO is 80 tonnes of lead instrumented with He-3 neutron detectors. Neutrinos from the supernova excite lead nuclei via both charged current (CC) and neutral current weak interactions to states from which one or two neutrons are ejected. The detection of these neutrons in HALOs He-3 detectors signals a galactic supernova. The time evolution of the luminosity, flavours and average neutrino energy give a direct window into supernova dynamics. The neutron excess of lead provides for a dominant sensitivity to CC interactions of the ν e flux. Modeling of supernovae combined with observational data, offers the possibility of extracting fundamental neutrino properties as well as advancing our understanding of the supernova mechanism. HALO at SNOLAB is modest in size and limited by statistics, more so the further the supernova, or the lower the neutrino energy. The decommissioning of the OPERA detector at LNGS in Italy makes 1.3 kT of lead available for the construction of a new detector, HALO-1kT, up to 30 times more sensitive than HALO. Also the new availability of He-3 from the US DOE opens a path to build more He-3 neutron counters. Support is requested for proof of principle measurements for the studies necessary to write a Technical Design Report. We also wish to join the COHERENT Collaboration to make the first measurement of neutrino-lead cross sections at supernova-relevant energies. The Spallation Neutron Source (SNS) at Oak Ridge National Laboratory produces intense pulses of neutrinos from pion and muon decay at rest. The existing HALO development data acquisition system, together with spare He-3 neutron detectors would enable us to easily measure the neutrino-lead cross section. Support is requested to transport this hardware to and from the SNS. This measurement would complete the calibration of HALO as well as help define the capabilities of HALO-1kT. Existing and planned neutrino detectors are only sensitive to supernovae occurring within our Galaxy. Only 2-3 are expected per century, so it is important to observe the next one with many detectors of diverse characteristics and sensitivities. Much was learnt from the 20 events from SN 1987A. Much more should be possible from the next galactic supernova.