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COUPP: First Results and Current Status Dark Matter Limits From a Bubble Chamber

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  1. COUPP: First Results and Current StatusDark Matter Limits From a Bubble Chamber 1 of 20

  2. 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 roomatthe rate of rate of ~1 kHz, so we certainly have our work cut out for us… 2 of 20

  3. 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) Normally this would cause boiling! Seitz model of bubble nucleation (classical BC theory): Threshold in deposited energy bg Threshold also in stopping power, allows for efficient, INTRINSIC MIP background rejection 3 of 20

  4. Conventional BC operation (high superheat, MIP sensitive) Low degree of superheat, sensitive to nuclear recoils only 60°C 40°C 40°C Muon Neutron(s) WIMP behavior 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 4 of 20

  5. 0.1 mm nucleation sites Liquid Solid The COUPP Approach to WIMP Detection: • Revisit 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 (fire-extinguishing industrial refrigerants), moderate pressure (180 psig) Spontaneous bulk nucleation rate = exp(-2.5e5)/(kg*day)!! (Tc= 122°C, but we run at ~30-40°C) Surface nucleations are produced by gas-filled voids, but we learned how to control them (cleaning, outgassing, buffer liquid, etc. – see astro-ph/0503398) 5 of 20

  6. 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. •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 Fluorine is best target for SD(p) Iodine has 2x reach of Ge for SI at 1 keV Fluorine is best target for SD Iodine has X3.5 reach of Ge for SI SD SUSY space harder to get to, but there are more robust predictions there (astro-ph/0001511, 0509269, and refs. therein) Spatial distribution of bubbles (~1 mm resolution) 6 of 20

  7. 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 FNALJ.I. Collar Sept 20 7 of 20

  8. Neutron and Gamma Calibrations in situ: 137Cs (13 mCi) Switchable Am/Be source (4.9 n/s) Best MIP rejection factor measured anywhere (~10-11 INTRINSIC, no data cuts) Blind absolute comparison with expectations (~30% uncertainty in those) Other experiments as references: XENON ~ 10-3 CDMS ~ 10-5 WARP ~ 10-8 First and foremost, a DM search needs to separate nuclear recoils from electron recoils. Low-energy WIMP-like recoil energy signal used in these calibrations 8 of 20

  9. 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) A look at initial data: Rn-domination 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… 9 of 20

  10. Science, Vol. 319, Feb. 15, 2008, pg. 933 First COUPP LimitsThe bubble chamber is back 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) …coming up… First COUPP results… 10 of 20

  11. 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 quickly decayed to equilibrium • 2009-10 goals: exploring SD “favored” region for the first time, and producing more competitive SI limits. A peek at our promising future (which is here already) (muon veto coincidence timing at work) 11 of 17 11 of 20

  12. Demonstrated by PICASSO • collaboration using Superheated • Droplet Detectors (arXiv:0807.1536). • Effect arises from much larger • number of acoustic sources • (protobubbles) along longer a ranges: • expected to be more dramatic in bulk • superheated liquid (bubble chambers). • Ongoing R&D to expand frequency • range and sensitivity of piezo • transducers used. • Could result into a DM detector • exclusively sensitive to WIMPs. dedicated chamber 12 of 20

  13. Next steps: 4, 15, 60 kg @ 330 mwe, then 60 at deeper site test site ~300 m.w.e. 13 of 20

  14. Next steps: 4, 15, 60 kg @ 330 mwe, then 60 at deeper site 14 of 20

  15. 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 15 of 20

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  18. Winter 2009 15 kg windowless prototype installation 18 of 20

  19. Winter 2009 15 kg windowless prototype installation 19 of 20

  20. Summary: • Easily scalable, room-T approach to DM detection: 4, 15, 60 kg chambers coming online. 500 kg design to follow. • ~10-11 intrinsic rejection of MIP backgrounds while fully sensitive to low-E recoils. • Best SD sensitivity, quickly approaching forefront in SI. • Promising acoustic a/n discrimination method being investigated right now • Deep underground deployment planed for 2010 (SNOlab or Soudan) 20 of 20

  21. Extra Transparencies 1 of 12

  22. 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). 2 of 12

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  26. The First Results (Science 15 February 2008: Vol. 319, no. 5865: pp. 933 – 936.Buzz-phrase: the bubble chamber is back.) 6 of 12

  27. Template For the Future: 7 of 12

  28. 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 SUSYparameter space. • High spatial granularity = additional n rejection mechanism • <$500/kg, room temperature operation, safe chemistry (fire-extinguishing 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 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 parameterspace 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! 8 of 12

  29. 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 (fire-extinguishing 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 WIMP signature: homogeneous distribution of singles (n-induced accumulate towards the exterior) Larger chambers will be “self-shielding” 9 of 12

  30. COUPP @ NuMI Tunnel (Fermilab Experiment E961) 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 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

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  32. LEGEND: green is carbon, red is fluorine, blue is iodine, black is argon. WIMP-nucleon SI cross-section of 1 pb 1000 GeV WIMP. 9 of 9 12 of 12