COUPP: First Results
Dark Matter Limits From a Bubble
Chamber
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TeV PA 2009
M.M. Szydagis 13 July
Direct Detection of Cold Dark Matter: The Challenge Ahead
• Non-baryonic Galactic Dark Matter close to a paradigm
(certainly in the minds of many), but yet to be detected.
• ~20-30% Cold (non-relativistic) DM presently favored
(we don’t seem to be able to explain large scale structure
of the universe without WIMPs–Weakly Interacting
Massive particles, relics of early stages)
• Cautious strategy: start by looking first for non-ad hoc
particle candidates, i.e., those already invoked by particle
theories (e.g., neutralino <-> MSSM, axions <-> strong CP problem)
• WIMPs: dominant interaction via low-energy nuclear elastic
scattering, expected rates << 1 per kg of target per day in keV region.
(local ~0.3-0.4 GeV/cm3, <v>~2-300 km/s, ~< 10-42 cm2).
Supersymmetric WIMPS can have rates as low as 1 recoil/ton/yr!
• The challenge: build cost-effective ton or multi-ton detectors
sensitive exclusively to WIMP-induced nuclear recoils (down to
one a year) and nothing else--not even neutron recoils.
• The scale of things: a 1 kg Ge detector fires in this room at the
rate of ~1 kHz, so we certainly have our work cut out for us…
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rate of
M.M. Szydagis 13 July
The COUPP Approach to WIMP Detection:
• Detection
of single bubbles
induced by high – dE /dx
nuclear recoils in heavy
liquid bubble chambers
1010 rejection factor for
MIPs. INTRINSIC (no data
cuts necessary)
•>
• Scalability:
large masses
easily monitored (built-in
“amplification”). Choice of
three triggers: pressure,
acoustic (ultrasound),
motion sensing (video)
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Normally this
would
cause boiling!
Seitz model of bubble
nucleation
(classical BC theory):
b
g
Threshold in deposited energy
Threshold also in
stopping power,
allows for efficient,
INTRINSIC
MIP background
rejection
TeV PA 2009
M.M. Szydagis 13 July
Conventional BC operation
(high superheat, MIP sensitive)
Muon
60°C
Low degree of superheat, sensitive to nuclear recoils only
40°C
Neutron(s)
WIMP behavior
40°C
Stereo view of a typical event in the 2 kg chamber
neutron-induced
nucleation in 20 cm3 CF3Br
(0.1 s real-time span)
Movie available from
http://cfcp.uchicago.edu/
~collar/bubble.mov
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The COUPP Approach to WIMP Detection:
• Revisit
Spontaneous bulk nucleation rate =
exp(-2.5e5)/(kg*day)!! (Tc= 122°C, but we run at ~30-40°C)
an old detector
technology with
improvements leading to
extended (unlimited?)
stability (ultra-clean BC: not
your daddy’s BC)
Moderate cost, moderate
temperature operation,
safe chemistry (fireextinguishing industrial
refrigerants), moderate
pressure (180 psig)
•
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Surface nucleations are produced by gas-filled
voids, but we learned how to control them (cleaning,
outgassing, buffer liquid, etc. – see astro-ph/0503398)
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nucleation sites
Liquid 0.1 mm
Solid
M.M. Szydagis 13 July
The COUPP Approach to WIMP Detection:
An old precept: an attack on both fronts
Excellent sensitivity to both SD and
SI couplings (CF3I)
•
Target fluid can be replaced (e.g.,
C3F8, C4F10, CF3Br). Useful for
separating WIMP- from n-induced
recoils and pinpointing WIMP in
SUSY parameter space.
•
Fluorine
is best
Fluorine
is best
target
for SD
target
for SD(p)
Iodine
Iodine
has has
X3.5 reach
2x reach
of Ge of
forGe
SI for
at 1SIkeV
Short mean free path for n’s =>
additional n-rejection mechanism
•
Single concentration: reducing emitters in fluids to levels already
achieved elsewhere (~10-17) will lead
to a complete probing of so-called
“natural” SUSY models
•
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SD SUSY space harder to
get to, but there are more
robust predictions there
(astro-ph/0001511, 0509269,
and refs. therein)
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Spatial
distribution
of bubbles
(~1 mm
resolution)
M.M. Szydagis 13 July
COUPP @
(Fermilab Test Beam
Proposal T945,
now experiment E961)
Concept similar to
1st Hydrogen BC
2 kg (1 L) CF3I engineering
prototype chamber built at
Uchicago, installed May ’05
evolution! …..
~80% livetime
test site @
~300 mwe
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UC HEP seminar
FNAL
J.I. Collar J.I.
Sept
Collar
20
Feb. 25
137Cs
(13 mCi)
Neutron and Gamma Calibrations in situ:
Best MIP rejection factor
measured anywhere
(<10-10 INTRINSIC,
no data cuts)
~10-13! (preliminary)
Other experiments
as references:
XENON ~ 10-3
CDMS ~ 10-5
WARP ~ 10-8
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Blind absolute
comparison with
expectations
(~30% uncertainty in those)
First and foremost, a DM search
needs to separate nuclear recoils
from electron recoils.
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Switchable
Am/Be source
(4.9 n/s)
Low-energy WIMP-like
recoil energy signal used in
these calibrations
M.M. Szydagis 13 July
A look at initial data: Rn-domination
Surface Events
• Surface (alpha) rate consistent with measured
50 ppb U and 30 ppb Th in standard quartz
• Tell-tale pressure sensitivity onset (’s)
• Can be rejected, but must be reduced by >10 to allow
for >60% live-time in ~50 kg (20 kg data shows promise)
• Addressed via modified etch during vessel
manufacture and use of synthetic silica (few ppt)
Bulk Events
• Rn sources present: viton o-ring, thoriated weld lines.
•Time correlations of bulk events are consistent with
3.1 minute half-life of Po-218. Max likelihood analysis
favors 100% Rn and 100% efficiency to it.
• Addressed by use of metallic gaskets, lanthanated
tips for flange welding, custom-made bellows (electron
beam welded) and SNO water (~1E-15 g/g U,Th).
when life
gives you
lemons…
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First COUPP Limits
The bubble chamber is back
Science, Vol. 319, Feb. 15, 2008, pg. 933
New limits exclude the low-mass region
favored by a SD interpretation of the
DAMA NaI signal
(last bastion for a conventional WIMP
explanation for DAMA)
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…coming up…
First COUPP
results…
M.M. Szydagis 13 July
A peek at our promising future (which is here already)
• New run of 1-liter chamber, started on
July 30, 2007, with Rn countermeasures in
place, has produced better-looking data.
• Some radon introduced during filling -but has long since decayed to equilibrium
• 2009-10 goals: exploring SD “favored”
region for the first time, and producing
more competitive SI limits.
COUPP (2kg, 2007)
COUPP (20kg, 2009),
muon veto
running, 300 mwe
(expected sensitivity)
(muon veto coincidence timing at work)
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M.M. Szydagis 13 July
Demonstrated by PICASSO
ollaboration using Superheated
roplet Detectors (arXiv:0807.1536).
Effect arises from much larger
umber of acoustic sources
protobubbles) along longer ranges:
xpected to be more dramatic in bulk
uperheated liquid (bubble chambers).
Ongoing R&D to expand frequency
ange and sensitivity of piezo
ransducers used.
Could result into a DM detector
xclusively sensitive to WIMPs.
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dedicated
chamber
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M.M. Szydagis 13 July
Next step: 20 kg @ 330 mwe, 100 kg target mass at SNOlab
test site
~300 m.w.e.
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Next step: 20 kg @ 330 mwe, 100 kg target mass at SNOlab
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Under construction at FNAL:
60 kg Chamber Completed water
tank veto/shield
for use with 60 kg
device
Commissioning to take place first
in the NUMI tunnel, prior to later
deployment even deeper underground
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Winter 2009 20 kg windowless prototype installation
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Winter 2009 20 kg windowless prototype installation
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Summary:
• Easily scalable, room-T
approach to DM detection:
20, 60 kg chambers coming
online. 500 kg design to
follow.
• ~10-13 intrinsic rejection of
MIP backgrounds while
fully sensitive to low-E
recoils.
• Best SD sensitivity,
quickly approaching
forefront in SI.
• Promising acoustic /n
discrimination method to
be investigated
• Deep underground
deployment planed for
2010 (Soudan or SNOlab)
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Extra Transparencies
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Physics Reach at Fermilab Site and Beyond
Background goal for E-961: << 1 events per kg per day
Spin-independent
Spin-dependent
~ 1c/kg-d expected from simulated (n). ~ 0.1c/kg-d is for 90% efficient veto.
A further reduction to ~0.03 c/kg-d is possible (simulated gallery n’s
percolate through 30 cm polyethylene shielding at that level).
By then better than 10-15 U,Th needed (World’s best is KAMLAND @ ~10-18).
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The First Results
(Science 15 February 2008: Vol. 319, no. 5865: pp. 933 – 936.
Buzz-phrase: the bubble chamber is back.)
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Template For the Future:
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M.M. Szydagis 13 July
The COUPP Approach to WIMP Detection:
• Detection of single bubbles induced by high – dE /dx
nuclear recoils in heavy liquid bubble chambers
• < 10-10 rejection factor for MIPs. INTRINSIC (no data cuts)
• Scalability:
large masses easily monitored (built-in
“amplification”). Choice of three triggers: pressure, acoustic
(ultrasound), motion sensing (video)
•
Revisit an old detector technology with improvements leading to
extended (unlimited?) stability (ultra-clean BC)
• Excellent sensitivity to both SD and SI couplings (CF3I)
• Target fluid can be replaced (e.g., C3F8, C4F10, CF3Br). Useful for
separating WIMP- from n-induced recoils and pinpointing WIMP in
SUSY parameter space.
• High spatial granularity = additional n rejection mechanism
• <$500/kg, room temperature operation, safe chemistry (fireextinguishing industrial refrigerants), moderate pressure (<200 psig)
• Single concentration: reducing -emitters in fluids to levels
already achieved elsewhere (~10-17) will lead to a complete probing of
“natural” SUSY models
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G. Bertone, D.G.
Cerdeno, J.I. Collar,
and B. Odom, Phys. Rev.
Lett. 99, 151301 (2007).
Rates measured in
CF3I and C3F8
(vertical bands)
tightly constrain
responsible SUSY
parameter space
and type of
WIMP
(LSP vs. LKKP)
Neutrons on the
other hand
produce
essentially the
same rates
in both
(n for F and I are
very similar)
Can take one’s
pick of a fluid –
they all
superheat!
The COUPP Approach to WIMP Detection:
• Detection of single bubbles induced by high – dE /dx
nuclear recoils in heavy liquid bubble chambers
• < 10-10 rejection factor for MIPs. INTRINSIC (no data cuts)
• Scalability:
large masses easily monitored (built-in
“amplification”). Choice of three triggers: pressure, acoustic
(ultrasound), motion sensing (video)
•
Revisit an old detector technology with improvements leading to
extended (unlimited?) stability (ultra-clean BC)
• Excellent sensitivity to both SD and SI couplings (CF3I)
• Target fluid can be replaced (e.g., C3F8, C4F10, CF3Br). Useful for
separating WIMP- from n-induced recoils and pinpointing WIMP in
SUSY parameter space.
• High spatial granularity = additional n rejection mechanism
• <$500/kg, room temperature operation, safe chemistry (fireextinguishing industrial refrigerants), moderate pressure (<200 psig)
• Single concentration: reducing -emitters in fluids to levels
already achieved elsewhere (~10-17) will lead to a complete probing
of “natural” SUSY models
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TeV PA 2009
WIMP
signature:
homogeneous
distribution
of singles
(n-induced
accumulate
towards the
exterior)
Larger chambers
will be “selfshielding”
M.M. Szydagis 13 July
COUPP @
NuMI Tunnel
(Fermilab Experiment
E961)
Nucleation rate at
surface and shallow
UC site (6 m.w.e.) in
good agreement with
environmental n’s
(a first “calibration”)
> 100 improvement
achieved at NuMI
n flux already
dominated by rock
radioactivity in a
site this deep. Muon
veto and 30 cm of
polyethylene allow to
reach ~0.03 c/kg-day
(= CDMS-II sensitivity)
KTeV
paddles
to be
reused
as COUPP
-veto
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LEGEND:
green is carbon,
red is fluorine,
blue is iodine,
black is argon.
WIMP-nucleon SI cross-section of 1 pb
1000 GeV WIMP.
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