Transcript Slide 1

HALO
- a Helium and Lead Observatory
Outline
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Overview
Motivation / Physics
SNEWS
Signal and Backgrounds
Monte Carlo studies
Further Work
SNOLAB Workshop IV, Sudbury, 15-17 August 2005
C.J. Virtue
Overview
• 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-term
Supernova detector
SNOLAB Workshop IV, Sudbury, 15-17 August 2005
C.J. Virtue
Motivation / Physics
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Galactic supernova are rare / little known
Unique opportunity
SNEWS
Lead; high v x-sect.,
low n cap. x-sect.
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 νe
• HALO’s sensitivity to νe
and NC valuable
SNOLAB Workshop IV, Sudbury, 15-17 August 2005
C.J. Virtue
NCD Energy Spectrum
Energy spectrum from
one NCD string with an
AmBe neutron source.
764-keV peak
191-keV shoulder from
proton going into the wall
SNOLAB Workshop IV, Sudbury, 15-17 August 2005
C.J. Virtue
Energy vs Duration
SNOLAB Workshop IV, Sudbury, 15-17 August 2005
C.J. Virtue
SNEWS – Supernova
Early Warning System
• 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+
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 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)
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
SNOLAB Workshop IV, Sudbury, 15-17 August 2005
C.J. Virtue
Monte Carlo Studies - GEANT
Phase 1 Work – 80 Tonne detector
– Use lead in its current geometry
– Start with single NCD per column of lead
(though ~300m available)
88 kg / block
865 blocks
8 kg /cm 3He
SNOLAB Workshop IV, Sudbury, 15-17 August 2005
C.J. Virtue
Monte Carlo Studies
Optimize for capture efficiency as
function of moderator thickness
42% capture efficiency
for 6mm polyethylene
moderator
Done in a fiducial volume
to avoid confusion from
edge-effects and to
understand maximum
efficiency.
SNOLAB Workshop IV, Sudbury, 15-17 August 2005
C.J. Virtue
Monte Carlo Studies
However, 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
SNOLAB Workshop IV, Sudbury, 15-17 August 2005
C.J. Virtue
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 m
2.7 kg/cm
41%
36
SNOLAB Workshop IV, Sudbury, 15-17 August 2005
C.J. Virtue
Monte Carlo Studies – phase 2
Optimize for full 700m of
3He counters
Allow modification of block
geometry if advantageous
Define footprint
SNOLAB Workshop IV, Sudbury, 15-17 August 2005
C.J. Virtue
Monte Carlo Studies
Detected
Neutrons
(SN @ 10kpc)
(phase 1)
Detected
Neutrons **
(SN @ 10kpc)
(phase 2)
Pb / 3He ratio
(700 m NCDs
- Phase 2)
Tonnes of Pb
Neutron
Capture
Efficiency
(fid. volume)
14 kg/cm
1000
55%
8 kg/cm
560
60%
(cf. 42% phase 1)
4 kg/cm
280
79%
87
2.7 kg/cm
189
83%
62
** - naïve scaling – not MC
SNOLAB Workshop IV, Sudbury, 15-17 August 2005
216
22/80 T
132
C.J. Virtue
Monte Carlo Studies
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
SNOLAB Workshop IV, Sudbury, 15-17 August 2005
C.J. Virtue
Further Work
• 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
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
SNOLAB Workshop IV, Sudbury, 15-17 August 2005
C.J. Virtue
Draft Budget
Capital costs 05-06 $CDN
Unit cost
Move 80 tonnes Pb to 6800
Etch surface
Move to final location
Schedule 80 PP moderator tubing
Steel platform
Framework for detector/reflector
Water boxes
Side panels
Unit
Qty
20
m
90
3
100
box
ea
400
5
Mechanical SubTotal
RF caps
Preamp connector and SHV
HV power supplies
LV power supplies
Rack
VME crate
Bit3
Shaper/ADCs
Preamps
Cables
Computer
Fiber Optic LAN
Total
18,000
5,000
1,000
1800
2000
3000
1200
500
32,500
10
ea
30
ea
700
ea
500
ea
500
ea
3000
ea
3500
ea
2000 8-ch card
100
ea
1 batch
5000
ea
3000
ea
Electronics Subtotal
Labor
Travel
Subtotal
Contingency
0.2
TOTAL
SNOLAB Workshop IV, Sudbury, 15-17 August 2005
50
50
4
4
1
2
2
12
100
5000
2
2
500
1500
2800
2000
500
6000
7000
24000
10000
5000
10000
6000
75300
50000
20000
177,800
35560
213,360
Thanks to Charles
Duba for this and
Slides from his
Presentation at
SNOLAB Workshop III
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
SNOLAB Workshop IV, Sudbury, 15-17 August 2005
C.J. Virtue