COUPP: First Results Dark Matter Limits From a Bubble Chamber TeV PA 2009 M.M. Szydagis 13 July 1 of 20

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  ~ GeV/cm 3, ~2-300 km/s,  ~< cm 2 ). 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 rate of ~1 kHz, so we certainly have our work cut out for us… Direct Detection of Cold Dark Matter: The Challenge Ahead 2 of 20 TeV PA 2009 M.M. Szydagis 13 July

Detection of single bubbles induced by high – dE /dx nuclear recoils in heavy liquid bubble chambers > 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) The COUPP Approach to WIMP Detection: Threshold also in stopping power, allows for efficient, INTRINSIC MIP background rejection Threshold in deposited energy 3 of 20 Normally this would cause boiling! Seitz model of bubble nucleation (classical BC theory): TeV PA 2009 M.M. Szydagis 13 July 

Conventional BC operation (high superheat, MIP sensitive) Low degree of superheat, sensitive to nuclear recoils only Neutron(s)WIMP behaviorMuon 60°C40°C 4 of 20 neutron-induced nucleation in 20 cm 3 CF 3 Br (0.1 s real-time span) Movie available from ~collar/bubble.mov TeV PA 2009 M.M. Szydagis 13 July Stereo view of a typical event in the 2 kg chamber

Spontaneous bulk nucleation rate = exp(-2.5e5)/(kg*day)!! (T c = 122°C, but we run at ~30-40°C) The COUPP Approach to WIMP Detection: Liquid 0.1 mm Solid nucleation sites Surface nucleations are produced by gas-filled voids, but we learned how to control them (cleaning, outgassing, buffer liquid, etc. – see astro-ph/ ) 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) 5 of 20 TeV PA 2009 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 (CF 3 I) Target fluid can be replaced (e.g., C 3 F 8, C 4 F 10, CF 3 Br). 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 (~ ) will lead to a complete probing of so-called “natural” SUSY models Fluorine is best target for SD Iodine has X3.5 reach of Ge for SI Spatial distribution of bubbles (~1 mm resolution) SD SUSY space harder to get to, but there are more robust predictions there (astro-ph/ , , and refs. therein) 6 of 20 Fluorine is best target for SD(p) Iodine has 2x reach of Ge for SI at 1 keV TeV PA 2009 M.M. Szydagis 13 July

UC HEP seminar J.I. Collar Feb. 25 FNAL J.I. Collar Sept 20 test ~300 mwe 2 kg (1 L) CF 3 I engineering prototype chamber built at Uchicago, installed May ’05 (Fermilab Test Beam Proposal T945, now experiment E961) Concept similar to 1st Hydrogen BC ~80% livetime evolution! ….. 7 of 20

Neutron and Gamma Calibrations in situ : 137 Cs (13 mCi) Best MIP rejection factor measured anywhere (< INTRINSIC, no data cuts) Blind absolute comparison with expectations (~30% uncertainty in those) Switchable Am/Be source (4.9 n/s) 8 of 20 TeV PA 2009 M.M. Szydagis 13 July Low-energy WIMP-like recoil energy signal used in these calibrations First and foremost, a DM search needs to separate nuclear recoils from electron recoils. ~ ! (preliminary) Other experiments as references: XENON ~ CDMS ~ WARP ~ 10 -8

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 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). Surface Events Bulk Events when life gives you lemons… 9 of 20 TeV PA 2009 M.M. Szydagis 13 July

First COUPP Limits The 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) First COUPP results… …coming up… 10 of 20 Science, Vol. 319, Feb. 15, 2008, pg. 933 TeV PA 2009 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 goals: exploring SD “favored” region for the first time, and producing more competitive SI limits. 11 of 17 (muon veto coincidence timing at work) TeV PA 2009 M.M. Szydagis 13 July COUPP (20kg, 2009), muon veto running, 300 mwe (expected sensitivity) COUPP (2kg, 2007) 11 of 20

dedicated chamber Demonstrated by PICASSO collaboration using Superheated Droplet Detectors (arXiv: ). Effect arises from much larger number of acoustic sources (protobubbles) along longer  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. 12 of 20 TeV PA 2009 M.M. Szydagis 13 July

test site ~300 m.w.e. Next step: mwe, 100 kg target mass at SNOlab 13 of 20

Next step: mwe, 100 kg target mass at SNOlab 14 of 20

Commissioning to take place first in the NUMI tunnel, prior to later deployment even deeper underground Under construction at FNAL: 60 kg Chamber Completed water tank veto/shield for use with 60 kg device TeV PA 2009 M.M. Szydagis 13 July 15 of 20

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Winter kg windowless prototype installation 18 of 20 TeV PA 2009 M.M. Szydagis 13 July

19 of 20 Winter kg windowless prototype installation TeV PA 2009 M.M. Szydagis 13 July

Summary: Easily scalable, room-T approach to DM detection: 20, 60 kg chambers coming online. 500 kg design to follow. ~ 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) 20 of 20 TeV PA 2009 M.M. Szydagis 13 July

Extra Transparencies 1 of 12 TeV PA 2009 M.M. Szydagis 13 July

Physics Reach at Fermilab Site and Beyond Spin-independentSpin-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 U,Th needed (World’s best is ~ ). Background goal for E-961: << 1 events per kg per day 2 of 12 TeV PA 2009 M.M. Szydagis 13 July

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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.) 6 of 12 TeV PA 2009 M.M. Szydagis 13 July

Template For the Future: 7 of 12 TeV PA 2009 M.M. Szydagis 13 July

Detection of single bubbles induced by high – dE /dx nuclear recoils in heavy liquid bubble chambers < 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 (CF 3 I) Target fluid can be replaced (e.g., C 3 F 8, C 4 F 10, CF 3 Br). 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 (~ ) will lead to a complete probing of “natural” SUSY models The COUPP Approach to WIMP Detection: Rates measured in CF 3 I and C 3 F 8 (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! G. Bertone, D.G. Cerdeno, J.I. Collar, and B. Odom, Phys. Rev. Lett. 99, (2007). 8 of 12

The COUPP Approach to WIMP Detection: Detection of single bubbles induced by high – dE /dx nuclear recoils in heavy liquid bubble chambers < 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 (CF 3 I) Target fluid can be replaced (e.g., C 3 F 8, C 4 F 10, CF 3 Br). 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 (~ ) will lead to a complete probing of “natural” SUSY models Larger chambers will be “self- shielding” WIMP signature: homogeneous distribution of singles (n-induced accumulate towards the exterior) 9 of 12 TeV PA 2009 M.M. Szydagis 13 July

KTeV paddles to be reused as COUPP  -veto 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) 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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LEGEND: green is carbon, red is fluorine, blue is iodine, black is argon. 9 of 9 TeV PA 2009 M.M. Szydagis 13 July WIMP-nucleon SI cross-section of 1 pb 1000 GeV WIMP. 12 of 12