Supernova Watches and
HALO
SNOLAB Grand Opening Workshop
May 14-16, 2012
Clarence J. Virtue
Supernova neutrinos –
First order expectations
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Approximate equipartition of neutrino fluxes
Several characteristic timescales for the phases of the explosion
(collapse, burst, accretion, cooling)
Time-evolving νe, νe, ν”μ” luminosities reflecting aspects of SN dynamics
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Presence of neutronization pulse
Hardening of spectra through accretion phase then cooling
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Fermi-Dirac thermal energy distributions characterized by a
temperature, Tν, and pinching parameter, ην
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Hierarchy and time-evolution of average energies at the neutrinosphere
T(ν”μ” ) > T(νe) > T(νe )
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ν-ν scattering collective effects and MSW oscillations
May 14, 2012
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Put another way...
An observed SN signal potentially has
information in its:
 The time evolution of the luminosities
 The time evolution of the average energies
 The values of the pinching parameters
 Deviation from the equiparition of fluxes
 Modifications of the above due to ν-ν
scattering collective effects and MSW
oscillations
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What is to be learned?
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Astrophysics
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Explosion mechanism
Accretion process
Black hole formation (cutoff)
Presence of Spherical accretion shock instabilities (3D effect)
Proto-neutron star EOS
Microphysics and neutrino transport (neutrino temperatures and
pinch parameters)
Nucleosynthesis of heavy elements
Particle Physics
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Normal or Inverted neutrino mass hierarchy, θ13
Presence of axions, exotic physics, or extra large dimensions
(cooling rate)
Etc.
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Opportunity to alert the
astronomical community
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Through participation in a global network of neutrino
sensitive detectors - SNEWS
Provide prompt and positive alert to astronomical
community in event of galactic SN in the event of a
coincidence between experiments
Also provides machinery for an “INDIVIDUAL”
announcement of SN by participating experiments
Design:
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Coincidence server(s) – 10 second UT time window
Maximum rate of alarms is 1 per 10 days per experiment
For 2-fold coincidence, 4 experiments  < 1 false
alarm/century
May 14, 2012
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SNEWS
– current configuration
Super-Kamiokande
LVD
Bologna
SSL
SSL
Redundant
Secure
Coincidence
Servers
SSL
10 s window
(UT time)
SSL
2-fold coincidence
Alert to the
Astronomical
Community
PGP signed e-mail
Borexino
IceCube
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PGP-signed e-mail
To amateur astronomers
Via Sky & Telescope
Go to skyandtelscope.com
to “subscribe to astroalert”
> 2000 subscribers
To neutrino physicists
and astronomers
Subscribe to receive an
alert at snews.bnl.gov
> 250 subscribers
Direct clients:
- Gravitational wave detectors
- Dark Matter detectors
- Gamma-ray burst Coordinates Network (GCN)
- etc.
• operating since March 23, 2004
• live since March 30, 2006
• all experiments sending automated alarms since April 17, 2006
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Super-Kamiokande
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50 kton water
Cerenkov
For 10 kpc SN
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7000 IBD
410 NC on 16O
300 ES
4◦ pointing
ES NC
νe CC
May 14, 2012
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Large Volume Detector
(LVD)
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1000 tonne liquid
scintillator with
PMTs and limited
streamer tubes
5 MeV threshold
M. Selvi, arXiv:hep-ex/0608061v1
May 14, 2012
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5160 PMTs
monitoring ~ 1 km3
of ice
~0.6 kt / PMT
(~3Mt for SN)
Statistical increase
in dark current /
singles rate (20 σ
at 30 kpc)
May 14, 2012
Astronomy and Astrophysics 535 (2011) A109
SNOLAB Grand Opening
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Borexino
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Liquid scintillator (PC)
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100 ton fiducial
300 ton viewed (SN)
For 10 kpc SN
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CC (IBD)
CC (12C)
NC (12C)
ES
79
5
23
5
L. Cadonati et al., Astropart.Phys.16:361-372,2002
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SNOLAB Grand Opening
νe CC ES
νe CC
NC
Includes
~100
νx + p
11
Near future experiments
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Gadzooks! (S-K plus Gd)
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MicroBoone (170 t LArTPC) 2014
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For DSNB detection through tagged IBD
SNEWS client (would buffer 1500 TB / ~30 minutes of
data containing 17 SN events for 10 kpc SN)
ICARUS
Noνa
HALO
SNO+
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Generically, how do we detect
a SN?
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We can instrument as large a mass as possible,
for as long as possible, and watch for a burst of
the subtle effects of the SN neutrino’s weak
interactions
We get to chose the target and the technology
To date we’ve concentrated almost exclusively
on electrons, protons, and PMTs
Some other “nuclear” targets are “along for the
ride” and only a few others seem worthy of
consideration
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The ideal SN detector would...
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Be reliable
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Target and detector would be stable and reliable for
decades
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Be large and scalable
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Low tech
Good aging properties  longevity
Target and detector technology should be modular and
easily expanded
Have large neutrino cross-sections
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Very helpful, constrains shielding and costs
Additionally, secondaries need sufficient mean free paths
to permit detection, constrains # readout channels and
costs
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The ideal detector would...
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Have diverse sensitivities to different reaction channels and the
ability to tag those channels on an event-by-event basis
Have a day job that does not conflict with supernova readiness
Be able to measure the energy and direction of the SN neutrinos
Have low background / noise levels above a threshold that
permits reliable SNEWS alerts from the far-side of the galaxy, or
much further.
Be able to record the data without loss from the nearest
conceivable SN
We don’t achieve all of this with any one technology!
... But HALO fills a niche
May 14, 2012
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HALO - a Helium and
Lead Observatory
A “SN detector of opportunity” / An evolution of
LAND – the Lead Astronomical Neutrino Detector,
C.K. Hargrove et al., Astropart. Phys. 5 183, 1996.
“Helium” – because of the availability of the
3He neutron detectors from the final phase of
SNO
+
“Lead” – because of high -Pb crosssections, low n-capture cross-sections,
complementary sensitivity to water Cerenkov
and liquid scintillator SN detectors
HALO is using lead blocks from a decommissioned cosmic
ray monitoring station
May 14, 2012
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Comparative ν-nuclear
cross-sections
Kate Scholberg
SNOwGLoBES
May 14, 2012
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Pb nuclear physics
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High Z increases νe CC cross-sections relative
to νe CC and NC due to Coulomb
enhancement.
CC and NC cross-sections are the largest of
any reasonable material though thresholds are
high ( CC-1n: 10.3 MeV, CC-2n: 18.4 MeV, NC1n: 7.4 MeV, NC-2n: 14.1 MeV)
Neutron excess (N > Z) Pauli blocks
further suppressing the νe CC channel
 Results in flavour sensitivity complimentary to
water Cerenkov and liquid scintillator detectors
Other Advantages
 High Coulomb barrier  no (α, n)
 Low neutron absorption cross-section (one of
the lowest in the table of the isotopes)  a
good medium for moderating neutrons down to
epithermal energies
May 14, 2012
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Flavour Sensitivities
Liquid
Scintillator
Water
Cherenkov
νe CC
νe CC
NC
NC
ES
νe CC
NC
May 14, 2012
νe CC
Lead
Liquid
Argon
(needs updating
for large θ13)
SNOLAB Grand Opening
Iron
NC
19
Goals and
Philosophy
Goals
 to provide νe (dominantly) and νx sensitivity to the SN
detection community as soon as possible
 to build a long-term, high live-time dedicated supernova
detector
 to explore the feasibility of scaling a lead-based detector to
kt mass
Philosophy
 Achieve these goals by keeping HALO
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Very low cost
Low maintenance
Low impact in terms of lab resources
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Design Overview
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Lead Array (79 +/- 1% tonnes)
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Neutron detectors
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4 three meter long 3He detectors per
column
384 meters total length
200 grams total 3He
Moderator
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32 three meter long columns of annular
Lead blocks
864 blocks total at 91kg each
HDPE tubing
Shielding (12 tonnes)
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30 cm of water (5 sides)
~18 cm average PE (bottom)
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Supernova signal
In 79 tonnes of lead for a SN @ 10kpc†,
CC:
 Assuming FD distribution with T=8 MeV for μ’s,
τ’s.
 68 neutrons through e charged current channels
 30 single neutrons
 19 double neutrons (38 total)
 20 neutrons through νx neutral current channels
 8 single neutrons
 6 double neutrons (12 total)
NC:
~ 88 neutrons liberated; ie. ~1.1 n/tonne of Pb
†- cross-sections from Engel, McLaughlin, Volpe, Phys. Rev. D 67, 013005 (2003)
For HALO neutron detection efficiencies of 50% have been
obtained in MC studies optimizing the detector geometry, the
mass and location of neutron moderator, and enveloping the
detector in a neutron reflector.
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HALO – March 2010
May 14, 2012
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3He
neutron detectors
Cutting apart welded sections
from SNO installation and
adding new endcaps. Six
months of careful work!
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Status today
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4/5th of shielding in
place
Cabling complete
Readout complete
HV on all channels and
full detector being readout since May 8th 2012.
Upgrade of electronics
pending
Calibration /
characterization started
Plans
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shielding compete in
June
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Participate in SNEWS
by year end
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Signal and
Backgrounds
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Performance
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Preamp / ADC pairing with best resolution (left)
Preamp / ADC pairing with best γ / n separation (right)
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Backgrounds and
SNEWS
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A trigger condition of 6 neutrons in a 2 second window gives
sensitivity out to ~20 kpc (for T=8 MeV for ”μ” )
Fast and thermal neutrons in SNOLAB occur at 4000 and 4100
neutrons/m2/day respectively
A background event rate of 150 mHz from all sources will
randomly satisfy the trigger condition once per month. We take
this as the target false alert rate for SNEWS (presently at 170
mHz with partial shielding)
Bulk α contamination in the CVD nickel tubes gives a negligible
22 +/- 1 events in neutron window per day for the whole array
(α, n) reactions not simulated in the HALO GEANT MC but the
threshold in Pb is 15.2 MeV
Cosmic ray muon rate is < 2 per day. Rate of spallation events
not yet calculated.
May 14, 2012
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Physics with HALO
K. Scholberg
March 2012 APS
May 14, 2012
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Physics with HALO
K. Scholberg
March 2012 APS
May 14, 2012
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Summary
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HALO is effectively complete and continuous
operation of the full detector began on May
8th providing sensitivity to the νe and νx
components of a supernova
HALO will participate in SNEWS once the
behaviour of the detector is well understood
Experience gained will feed into the design of
a next generation detector taking advantage
of the scalability of the lead plus neutron
detector technology
May 14, 2012
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The HALO
Collaboration
With assistance this past year from:
Kurt Nicholson – Guelph U.
Axel Boeltzig – TU Dresden
Ben Bellis, Leigh Schaefer, Zander Moss – Duke U.
Victor Buza, Olivia Zigler – U. Minnesota Duluth
Brian Redden – Armstrong Atlantic State U
Thomas Corona – U. North Carolina
Andre-Philippe Olds – Laurentian U.
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