Silicon Burning Neutrinos at Super-K with Gadolinium Charles Simpson, for the Super-Kamiokande Collaboration References [1] GADZOOKS! Anti-neutrino spectroscopy with large water Cherenkov detectors, J.F. Beacom and M.R. Vagins, PRL 93 (2004) [2] Odrzywolek et al. doi.org/10.1063/1.2818538 [3] Odrzywolek th.if.uj.edu.pl/~odrzywolek/ [4] A. Barna and S. Dye, “Web Application for Modeling Global Antineutrinos,” arXiv:1510.05633 1. Super-Kamiokande • 50 ktons water, 22.5 kton fiducial volume • Instrumented with 11129 20 inch PMTs • Detects Cherenkov light from charged particles passing though water • Already hugely successful in proton decay searches and neutrino detection • Soon to be upgraded for next phase with Gadolinium doping • By adding 0.2% Gd salt by mass, will detect up to 80% of neutrons [1]. 2. Thermal Neutron Capture on Gadolinium • Isotopes of Gadolinium have some of the highest cross sections for thermal neutron capture[1]. • Neutron capture followed by gamma ray cascade of around 8 MeV within 20 microseconds; enough energy to be reliably detected in Super-K. • Neutron capture gammas are studied using MC • Background is modelled using real data taken in SK e+ p n g Gd ne g g often invisible thermalisation 3. Pre-Supernova Silicon Burning Neutrinos • Extra early supernova warning for nearby stars – before the usual supernova neutrino signal • Never before seen astrophysical object, not visible to EM astronomy! • Massive star prior to core collapse • Star running out of H and He • Contracts and gets hotter • Heavier nuclei are fused • Rapid increase to production of neutrinos and antineutrinos [2] • At SK-Gd, detection efficiency for antineutrinos will be increased by neutron detection Time to SN in hours 250 − 200 − 150 − 100 − 50 − 0 Events per hour 2 − 10 1 − 10 1 10 2 10 Odrzywolek 15M Odrzywolek 25M Signal event rate at 0.2kpc Rapid increase in event rate at SK before supernova Data from [2] and [3] 6. Summary and Conclusion • The next stage of Super- Kamiokande is doping with gadolinium for efficient neutron tagging • A supernova is often preceded by silicon burning • Silicon burning rapidly increases the electron antineutrino luminosity and average energy – can be detected by SK-Gd • Main backgrounds are intrinsic radioactivity and reactor neutrinos • SK-Gd would detect this for a star up to 900 parsecs away • Up to 60 hours early warning before Betelgeuse goes supernova Supernova Neutrinos Silicon Burning Neutrinos Mean Energy ~20 MeV Mean Energy ~2 MeV Hours before light from SN Days before light from SN Detected in 1987 Never detected before 1000s of events in seconds at SK at >10kpc 100s of events in a day at SK-Gd for stars at <1kpc 5. How much warning and range? • Depends on mass of star, and the mass hierarchy! • Some uncertainty in intrinsic background and Japanese nuclear reactor situation • Max warning for Betelgeuse is ~60 hours (1 per 2 year type-II error rate assumed) • Max range for 3σ discovery ~900 parsecs • There are 41 red super giants in this range • Low energy backgrounds at SK are intrinsic radioactivity and cosmic muon spallation products • Look for neutron capture candidates in coincidence with very low energy positron candidates • Main background may be reactor neutrinos – will depend on Japanese nuclear reactors • Alarm would watch for an increase in the rate of candidate events • Compare the last day with the last 30 days and do a hypothesis test on Poisson distribution • Likelihood threshold set by type-II error rate: is 1 false alarm per month OK? 1 per year? 1 per 10 years? Reactor data from [4] Positron candidate total energy (MeV) 0 1 2 3 4 5 6 7 8 Events per 24 hours per 0.20 MeV 1 - 10 1 10 Final 24 hours at 150 parsec Accidental BG BG ν Reactor and Geo Silicon burning signal, 15M 150pc 25M 4. Backgrounds Distance (kparsec) 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Warning time (hours) -1 10 1 10 2 10 Normal Hierarchy solar 15 M Normal Hierarchy solar 25 M Inverted Hierarchy solar 1