SNOLAB Workshop V, Sudbury, August 2006 C.J. Virtue HALO - a Helium and Lead Observatory Outline Overview Motivation / Physics SNEWS Signal and Backgrounds Monte Carlo studies Further Work

SNOLAB Workshop V, Sudbury, August 2006 C.J. Virtue Use materials on hand (Phase 1) –80 tonnes of Pb from decommissioned Deep River Cosmic-ray station – 3 He proportional counter neutron detectors plus DAQ from SNO; plus possibly 10 BF 3 counters To produce a –Low cost –Low maintenance –Low impact in terms of lab resources (space) –Long-term, high livetime Supernova detector Overview – an opportunity

SNOLAB Workshop V, Sudbury, August 2006 C.J. Virtue Galactic supernova are rare / little known Unique opportunity for particle physics, astronomers, SN dynamics SNEWS Lead; high x-sect., low n cap. x-sect. Motivation / Physics

SNOLAB Workshop V, Sudbury, August 2006 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

SNOLAB Workshop V, Sudbury, August 2006 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; “Individual” non-coincident alerts also possible now > 250 subscribers to distribution list > 2000 amateur subscribers through Sky & Telescope GCN (Gamma-ray burst Coordinates Network) HALO could bridge a gap between SNO and SNO+ SNEWS – Supernova Early Warning System

SNOLAB Workshop V, Sudbury, August 2006 C.J. Virtue SNO’s NCD 3 He counters Current plan is for NCD removal from SNO in February & March of Close to 700 m of low background 3 He counters would be stored underground until HALO deployment. Space in SNOLAB available early 2008.

SNOLAB Workshop V, Sudbury, August 2006 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.

SNOLAB Workshop V, Sudbury, August 2006 C.J. Virtue SN neutrino signal in HALO – Phase 1 In 80 tons of lead for a 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; ie. 1.1 n/T †- Engel, McLaughlin, Volpe, Phys. Rev. D 67, (2003)

SNOLAB Workshop V, Sudbury, August 2006 C.J. Virtue Phase 1 Work – 80 Tonne detector –Use lead in its current geometry –Shown with single NCD per column of lead (total of 95 m of counters) Monte Carlo Studies - GEANT 88 kg / block 865 blocks 8 kg /cm 3 He

SNOLAB Workshop V, Sudbury, August 2006 C.J. Virtue Optimize for capture efficiency as function of moderator thickness Monte Carlo Studies – Phase 1 42% capture efficiency for 6mm polypropylene moderator Done in a fiducial volume to avoid confusion from edge-effects and to understand maximum efficiency.

SNOLAB Workshop V, Sudbury, August 2006 C.J. Virtue However, with only 80 T the volume- averaged efficiency falls to 17.5% (60% loss relative to “fiducial volume” one) Add reflector 20 cm water adequate recover to 25% capture efficiency (volume averaged); 40% loss reduces external neutron background from 0.1Hz from thermal flux to 0.002Hz from ~ Hz to 0.04 Hz for fast flux Monte Carlo Studies – Phase 1

SNOLAB Workshop V, Sudbury, August 2006 C.J. Virtue Other Backgrounds Internal alphas in n-region –3.5x10 -4 Hz*Length/200m Cosmic ray induced neutrons –1.3x10 -5 (ε) Hz –Multi-neutron bursts thermalize in ~200μs Gamma Backgrounds –< 1x10 -5 Hz ie. small for burst detection, but still a need for more detailed simulation of backgrounds with emphasis on external neutrons

SNOLAB Workshop V, Sudbury, August 2006 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 10kpc) 195 m8 kg/cm25% m4 kg/cm35% m2.7 kg/cm41%36

SNOLAB Workshop V, Sudbury, August 2006 C.J. Virtue Monte Carlo Studies – Phase 2 Optimize for full 700m of 3 He counters (and possibly 140 m of 10 BF 3 counters) Allow for modification of block geometry and for purchase of additional Pb.

SNOLAB Workshop V, Sudbury, August 2006 C.J. Virtue Phase 2 Monte Carlo Studies Choice of moderator – D 2 O versus polypropylene? Twice the volume required; O($700K) No significant gain in neutron capture efficiency – dominated by neutron leakage not competition for neutron capture Stick with plastics! Distribution of moderator – various options simulated – best efficiency and least material for moderator surrounding 3 He counters

SNOLAB Workshop V, Sudbury, August 2006 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 10kpc) (Phase 1) Detected Neutrons ** 10kpc) (Phase 2) 14 kg/cm100055% kg/cm560 60% (cf. 42% - phase 1) 22/80 T238 4 kg/cm28079%31/80 T kg/cm18983%36/80 T83 ** - preliminary

SNOLAB Workshop V, Sudbury, August 2006 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 - needs further MC work to define Good news – 1 kT of Pb occupies a cube only 4.5 m on a side; O($1M material) Detailing costing and design for Phase 2 still to come … Monte Carlo Studies

SNOLAB Workshop V, Sudbury, August 2006 C.J. Virtue Continue with refinement of MC work – SN modeling; sensitivity of Phase 2 to additional physics – update Pb cross-sections, neutron energy distributions – Modeling of backgrounds – finalize design of Phase 2 detector Engineering work for Phase 1 installation Get ready for installation as space becomes available Further Work

SNOLAB Workshop V, Sudbury, August 2006 C.J. Virtue SNOLAB Requirements – Phase 1 3x3x3m cube for optimum efficiency –Other configurations are possible Hallway would be optimum for future expansion Overhead crane for setup and movement UPS power and remote access for 100% livetime Early start date

SNOLAB Workshop V, Sudbury, August 2006 C.J. Virtue Draft Budget – Phase 1 Thanks to Charles Duba for this and other slides from his presentation at SNOLAB Workshop III

SNOLAB Workshop V, Sudbury, August 2006 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