SNOLAB Workshop IV, Sudbury, 15-17 August 2005 C.J. Virtue HALO - a Helium and Lead Observatory Outline Overview Motivation / Physics SNEWS Signal and

SNOLAB Workshop IV, Sudbury, 15-17 August 2005 C.J. Virtue

HALO - a Helium and Lead

ObservatoryOutline

• Overview• Motivation / Physics• SNEWS• Signal and Backgrounds• Monte Carlo studies• Further Work


• Use materials on hand– 80 tonnes of Pb from decommissioned Chalk

River Cosmic-ray station– 3He proportional counter neutron detectors

• To produce a – Low cost– Low maintenance– Low impact in terms of lab resources– Long-termSupernova detector

Overview


• Galactic supernova are rare / little known• Unique opportunity• SNEWS• Lead; high v x-sect.,

low n cap. x-sect.

Motivation / Physics


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 νe

• HALO’s sensitivity to νe and NC valuable


NCD Energy Spectrum

191-keV shoulder from proton going into the wall

764-keV peakEnergy spectrum from one NCD string with an AmBe neutron source.


Energy vs Duration


• 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


Signal

• In 80 tons of lead for a SN @ 10kpc†,– Assuming LMA, FD distribution around

T=8 MeV for νμs, ντs.– 68 neutrons through νe charged current

channels• 30 single neutrons• 19 double neutrons (38 total)

– 21 neutrons through νx neutral current channels

• 9 single neutrons• 6 double neutrons (12 total)

• ~89 neutrons liberated

†- Engel, McLaughlin, Volpe, Phys. Rev. D 67, 013005 (2003)


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


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 / block865 blocks8 kg /cm 3He


Optimize for capture efficiency as function of moderator thickness

Monte Carlo Studies

42% capture efficiencyfor 6mm polyethylenemoderator

Done in a fiducial volumeto avoid confusion fromedge-effects and to understand maximumefficiency.


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


Monte Carlo Studies – phase 1

# NCDs per column

Total NCD length

Pb / 3He ratio(80 Tonnes Pb

- Phase 1)

Neutron Capture

Efficiency(vol. aver.)

Detected Neutrons

(SN @ 10kpc)

1 95 m 8 kg/cm 25% 22

2 190 m 4 kg/cm 35% 31

3 285 m2.7

kg/cm41% 36


Monte Carlo Studies – phase 2

Optimize for full 700m of3He counters

Allow modification of blockgeometry if advantageous

Define footprint


Monte Carlo Studies

Pb / 3He 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/cm 1000 55% 216

8 kg/cm 560

60%(cf. 42% - phase

1)

22/80 T 132

4 kg/cm 280 79% 87

2.7 kg/cm

189 83% 62

** - naïve scaling – not MC


Phase 2 Interpretation - More is better; but what is optimum?

• # of 2n events detected varies mass * capture efficiency 2

• Optimizing on m*ε2 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


• 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


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


Capital costs 05-06 $CDNUnit cost Unit Qty Total

Move 80 tonnes Pb to 6800 18,000Etch surface 5,000Move to final location 1,000Schedule 80 PP moderator tubing 20 m 90 1800Steel platform 2000Framework for detector/reflector 3000Water boxes 3 box 400 1200Side panels 100 ea 5 500

Mechanical SubTotal 32,500RF caps 10 ea 50 500Preamp connector and SHV 30 ea 50 1500HV power supplies 700 ea 4 2800LV power supplies 500 ea 4 2000Rack 500 ea 1 500VME crate 3000 ea 2 6000Bit3 3500 ea 2 7000Shaper/ADCs 2000 8-ch card 12 24000Preamps 100 ea 100 10000Cables 1 batch 5000 5000Computer 5000 ea 2 10000Fiber Optic LAN 3000 ea 2 6000

Electronics Subtotal 75300Labor 50000Travel 20000Subtotal 177,800Contingency 0.2 35560TOTAL 213,360

Draft Budget

Thanks to CharlesDuba for this and Slides from his Presentation at SNOLAB Workshop III


Collaboration Members as of 8/05

University of WashingtonPeter Doe, Charles Duba, Joe Formaggio, Hamish Robertson, John

Wilkerson

Laurentian UniversityJacques Farine, Clarence Virtue, Fabrice Fleurot, Doug Hallman

Los Alamos National LaboratoryJaret Heise, Andrew Hime

Lawrence Berkeley National LaboratoryKevin Lesko

Carleton UniversityCliff Hargrove, David Sinclair

Queen’s UniversityFraser Duncan, Tony Noble

Duke UniversityKate Scholberg

University of Minnesota DuluthAlec Habig

Documents

SNOLAB Workshop IV, Sudbury, 15-17 August 2005 C.J. Virtue HALO - a Helium and Lead Observatory Outline Overview Motivation / Physics SNEWS Signal and