1. SNOLAB Workshop IV, Sudbury, 15-17 August 2005 C.J. Virtue HALO - a Helium and Lead Observatory Outline Overview Motivation / Physics SNEWS Signal and Backgrounds Monte Carlo studies Further Work

2. SNOLAB Workshop IV, Sudbury, 15-17 August 2005 C.J. Virtue Use materials on hand –80 tonnes of Pb from decommissioned Chalk River Cosmic-ray station – 3 He proportional counter neutron detectors To produce a –Low cost –Low maintenance –Low impact in terms of lab resources –Long-term Supernova detector Overview

3. SNOLAB Workshop IV, Sudbury, 15-17 August 2005 C.J. Virtue Galactic supernova are rare / little known Unique opportunity SNEWS Lead; high v x-sect., low n cap. x-sect. Motivation / Physics

4. SNOLAB Workshop IV, Sudbury, 15-17 August 2005 C.J. Virtue Neutrinos from supernovae Neutrinos leaving star are expected to be in a Fermi-Dirac distribution according to escape depth: Oscillations redistribute neutrino temperatures SK, Kamland are primarily sensitive to ν e HALO’s sensitivity to ν e and NC valuable

5. SNOLAB Workshop IV, Sudbury, 15-17 August 2005 C.J. Virtue NCD Energy Spectrum 191-keV shoulder from proton going into the wall 764-keV peak Energy spectrum from one NCD string with an AmBe neutron source.

6. SNOLAB Workshop IV, Sudbury, 15-17 August 2005 C.J. Virtue Energy vs Duration

7. SNOLAB Workshop IV, Sudbury, 15-17 August 2005 C.J. Virtue Inter- experiment collaboration to disseminate the news of a galactic SN Coincidence between detectors required in 10 second window SNEWS is “live” – a “GOLD” coincidence would be sent to subscribers > 250 subscribers to e-mail distribution list > 2000 amateur subscribers through Sky & Telescope GCN (Gamma-ray burst Coordinates Network) Amanda joined recently; Kamland soon HALO could bridge a gap between SNO and SNO+ SNEWS – Supernova Early Warning System

8. SNOLAB Workshop IV, Sudbury, 15-17 August 2005 C.J. Virtue Signal In 80 tons of lead for a SN @ 10kpc †, –Assuming LMA, FD distribution around T=8 MeV for ν μ s, ν τ s. –68 neutrons through ν e charged current channels 30 single neutrons 19 double neutrons (38 total) –21 neutrons through ν x neutral current channels 9 single neutrons 6 double neutrons (12 total) ~89 neutrons liberated †- Engel, McLaughlin, Volpe, Phys. Rev. D 67, 013005 (2003)

9. SNOLAB Workshop IV, Sudbury, 15-17 August 2005 C.J. Virtue Backgrounds Norite (α,n) neutrons –0.1(ε) Hz Internal alphas in n-region –3.5x10 -4 Hz*Length/200m Cosmic ray neutrons –1.3x10 -5 (ε) Hz –Multi-neutron bursts thermalize in ~200μs Gamma Backgrounds –< 1x10 -5 Hz

10. SNOLAB Workshop IV, Sudbury, 15-17 August 2005 C.J. Virtue Phase 1 Work – 80 Tonne detector –Use lead in its current geometry –Start with single NCD per column of lead (though ~300m available) Monte Carlo Studies - GEANT 88 kg / block 865 blocks 8 kg /cm 3 He

11. SNOLAB Workshop IV, Sudbury, 15-17 August 2005 C.J. Virtue Optimize for capture efficiency as function of moderator thickness Monte Carlo Studies 42% capture efficiency for 6mm polyethylene moderator Done in a fiducial volume to avoid confusion from edge-effects and to understand maximum efficiency.

12. SNOLAB Workshop IV, Sudbury, 15-17 August 2005 C.J. Virtue However, volume-averaged efficiency falls to 17.5% (60% loss relative to “fiducial volume” one) Monte Carlo Studies Add reflector 20 cm water adequate recover to 25% capture efficiency (volume averaged); 40% loss

13. SNOLAB Workshop IV, Sudbury, 15-17 August 2005 C.J. Virtue Monte Carlo Studies – phase 1 # NCDs per column Total NCD length Pb / 3 He ratio (80 Tonnes Pb - Phase 1) Neutron Capture Efficiency (vol. aver.) Detected Neutrons (SN @ 10kpc) 195 m8 kg/cm25%22 2190 m4 kg/cm35%31 3285 m2.7 kg/cm41%36

14. SNOLAB Workshop IV, Sudbury, 15-17 August 2005 C.J. Virtue Monte Carlo Studies – phase 2 Optimize for full 700m of 3 He counters Allow modification of block geometry if advantageous Define footprint

15. SNOLAB Workshop IV, Sudbury, 15-17 August 2005 C.J. Virtue Monte Carlo Studies Pb / 3 He ratio (700 m NCDs - Phase 2) Tonnes of Pb Neutron Capture Efficiency (fid. volume) Detected Neutrons (SN @ 10kpc) (phase 1) Detected Neutrons ** (SN @ 10kpc) (phase 2) 14 kg/cm100055%216 8 kg/cm560 60% (cf. 42% - phase 1) 22/80 T132 4 kg/cm28079%87 2.7 kg/cm18983%62 ** - naïve scaling – not MC

16. SNOLAB Workshop IV, Sudbury, 15-17 August 2005 C.J. Virtue Phase 2 Interpretation - More is better; but what is optimum? # of 2n events detected varies mass * capture efficiency 2 Optimizing on m* ε 2 with fiducial volume efficiency suggests optimum near 1.5kT, but - insufficient points done - using volume averaged efficiency will reduce the optimum mass, suspect closer to 1kT - needs further MC work to define Good news – 1 kT of Pb occupies a cube only 4.5 m on a side - great quality Pb (Doe Run) ~1.5M USD / kT, but this quality is not required Monte Carlo Studies

17. SNOLAB Workshop IV, Sudbury, 15-17 August 2005 C.J. Virtue Continue with refinement of MC work – SN modeling – Pb cross-sections – Neutron energy distributions –Modeling of backgrounds – design of phase 2 detector Engineering work for phase 1 installation Ready for installation as space becomes available Further Work

18. SNOLAB Workshop IV, Sudbury, 15-17 August 2005 C.J. Virtue SNOLAB Requirements 3x3x3m cube for optimum efficiency –Other configurations are possible Hallway would be optimum for future expansions Overhead crane for setup and movement UPS power and remote access for 100% livetime Earliest possible start date

19. SNOLAB Workshop IV, Sudbury, 15-17 August 2005 C.J. Virtue Draft Budget Thanks to Charles Duba for this and Slides from his Presentation at SNOLAB Workshop III

20. SNOLAB Workshop IV, Sudbury, 15-17 August 2005 C.J. Virtue Collaboration Members as of 8/05 University of Washington Peter Doe, Charles Duba, Joe Formaggio, Hamish Robertson, John Wilkerson Laurentian University Jacques Farine, Clarence Virtue, Fabrice Fleurot, Doug Hallman Los Alamos National Laboratory Jaret Heise, Andrew Hime Lawrence Berkeley National Laboratory Kevin Lesko Carleton University Cliff Hargrove, David Sinclair Queen’s University Fraser Duncan, Tony Noble Duke University Kate Scholberg University of Minnesota Duluth Alec Habig